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What is the biological reason for a burst appendix being potentially lethal?
Given that the appendix does not seem to be used by the human body, what is the biological reason that it is potentially lethal when this organ bursts?
Also, what would cause the 'burst'?
Necessary conditions
In order for the process culminating in appendiceal rupture to begin, there must first be proximal obstruction of the lumen (the inside cavity of the appendix) that prevents normal communication with the bowel.
Obstruction is most commonly caused by a fecalith, which results from accumulation and inspissation of fecal matter around vegetable fibers. The bowel wall inside the (now closed) appendix continues to secrete muscous, and bacteria continue to multiply, producing the distention that is often perceived as nausea, vomiting, and poorly localized abdominal pain.1
The process leading to rupture
As the pressure in the appendix increases, venous pressure is exceeded. This means blood can no longer exit the venules of the appendix normally. In the presence of ongoing arterial flow, this leads to vascular engorgement, worsening the distention and increasing pressure further. The inflammatory process spreads from the lumen (inside) of the appendix to the serosa (outside) and then to the parietal peritoneum (lining of the abdominal cavity). This last step is what causes the characteristic shift in pain from poorly localized visceral pain to focal right lower quadrant pain.
As distention worsens, arterial pressure is eventually exceeded, and the most poorly vascularized areas of the appendix (generally just beyond the point of obstruction on the antimesenteric border) infarct first. Dead tissue has very little structural integrity, and once infarction happens perforation is likely to follow quickly.
Why this is (sometimes) lethal
There are several possible mechanisms, more than one of which is probably operative in most cases.
The three I have listed below all converge on the same final common pathway: In the absence of adequate systemic blood pressure (shock), the heart is not able to pump normally and will eventually deteriorate into a non-perfusing rhythm (a.k.a death).
Bacteria in the peritoneal cavity: As in bowel perforation of any cause (e.g. perforated peptic ulcer, perforated diverticulum, traumatic perforation), bacteria in the peritoneal cavity (the "free space" outside the bowel within the abdomen) triggers an intense inflammatory reaction and fluid sequestration. Fluid pulled from the circulation into the peritoneal space causes hypotension and (hypovolemic) shock.
Infarcted bowel: Dead tissue connected to the body is never a good situation. Intracellular contents are released into the bloodstream - electrolyte release can cause hyperkalemia and other electrolyte imbalances; reactive oxygen species can lead to hypotension and (distributive) shock.
Sepsis: Bacteria (generally gram negative rods from among normal gut flora - most commonly Escherichia coli or Bacteroides fragilis) may enter the bloodstream due to compromised vessels during the process of infarction and rupture. Lipopolysaccharides in the cell wall of gram-negative bacterial organisms lead to activation of monocytes and macrophages. This results in increased levels of interleukin-1 and tumor necrosis factor and eventually of IL-6 and IL-8. These cause widespread endothelial injury leading to diffuse alveolar damage in the lungs and activation of the coagulation system leading to disseminated intravascular coagulation. These cytokines also lead to systemic vasodilation and (distributive, septic) shock.
1. Silen W. Chapter 300. Acute Appendicitis and Peritonitis. In: Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson J, Loscalzo J. eds. Harrison's Principles of Internal Medicine, 18e. New York, NY: McGraw-Hill; 2012.
2. Kemp WL, Burns DK, Brown TG. Chapter 8. Hemodynamics. Pathology: The Big Picture. New York, NY: McGraw-Hill; 2008.
3. Charles Brunicardi, F. Acute Appendicitis. Schwartz's Manual of Surgery; 2006.
The appendix doesn't burst by itself. It just lives there quietly, not causing problems.
But if it gets infected, it gets full of bacteria, their waste (frequently toxic), and whatever liquids your body exuded into it to fight the infection. It is also connected to your digestive tract, which contains half-digested food.
When the appendix swells due to the infection, the pressure can build up enough that it bursts - unlike, say, the bladder, which also can be infected, and also has a baglike shape, but it also has a way to get emptied, which reduces the pressure. It is like having a boil filled with pus, you know how the skin on them gets thin and can burst. But this boil is inside of you, not on the outside.
And once it's burst, all this pus goes into your bloodstream, full of bacteria and toxins. If this is not treated, you get sepsis and die.
This is the biological mechanism for dying from burst appendix.If by reason you are asking why we have a useless organ which can kill us - nobody knows for sure, but our best guess is that evolution just hasn't gotten around to get rid of it. It served a function once, and has been getting smaller and smaller since then, but the genes which cause it to appear haven't yet been bred out of humanity.
As pointed out in the comment, it is not a useless organ (turns out my biology teacher in highschool was wrong). It has a function, and just like any other organ, it is useful while healthy and can kill you if it gets a disease.
Ectopic Pregnancy (Tubal Pregnancy)
An ectopic pregnancy is a pregnancy located outside the inner lining of the uterus. The Fallopian tubes are the most common locations for an ectopic pregnancy.
What are the signs and symptoms of ectopic pregnancy?
The three symptoms (characteristics) of ectopic pregnancy are abdominal pain, absence of menstrual periods (amenorrhea), and vaginal bleeding. However, only about 50% of women have all three of these symptoms.
What causes and ectopic pregnancy?
Ectopic or tubal pregnancy is caused when a fertilized egg lodges in a Fallopian tube or other location instead of continuing its journey to the uterus, where it is supposed to implant. The egg can become stuck when a Fallopian tube is damaged, scarred, or distorted.
What are the risk factors for ectopic pregnancy?
Risk factors for ectopic pregnancy include previous ectopic pregnancies and conditions (surgery, infection) that disrupt the normal anatomy of the Fallopian tubes. The major health risk of an ectopic pregnancy is rupture, leading to internal bleeding.
What is the percentage of women who have an ectopic pregnancy?
Ectopic pregnancy occurs in 1%-2% of all pregnancies.
What exams, tests, or procedures diagnose ectopic pregnancy?
Diagnosis of ectopic pregnancy is usually established by blood hormone tests and pelvic ultrasound.
What treatments are available for ectopic pregnancy? Will you need surgery?
Treatment options for ectopic pregnancy include both surgery and medication.
Bleeding in Early Pregnancy
Causes of bleeding during first trimester
Serious causes of bleeding during the first trimester of pregnancy include:
Threatened miscarriage
Subchorionic hemorrhage
If you notice any bleeding during any stage of pregnancy, call your doctor.
What is the medical definition of ectopic pregnancy?
An ectopic pregnancy is an early pregnancy that occurs outside of the normal location (uterine lining) for a developing pregnancy. Most ectopic pregnancies occur in the Fallopian tubes. An ectopic pregnancy cannot progress normally and typically results in the death of the embryo or fetus.
What is an ectopic pregnancy? What does an ectopic pregnancy look like (picture)?
An ectopic pregnancy (EP) is a condition in which a fertilized egg settles and grows in any location other than the inner lining of the uterus. The vast majority of ectopic pregnancies are so-called tubal pregnancies and occur in the Fallopian tube. However, they can occur in other locations, such as the ovary, cervix, and abdominal cavity. An ectopic pregnancy occurs in about one in 1%-2% of all pregnancies. A molar pregnancy differs from an ectopic pregnancy in that it is usually a mass of tissue derived from an egg with incomplete genetic information that grows in the uterus in a grape-like mass that can cause symptoms to those of pregnancy.
The major health risk of ectopic pregnancy is rupture leading to internal bleeding. Before the 19th century, the mortality rate (death rate) from ectopic pregnancies exceeded 50%. By the end of the 19th century, the mortality rate dropped to five percent because of surgical intervention. Statistics suggest that with current advances in early detection, the mortality rate has improved to less than five in 10,000. The survival rate from ectopic pregnancies is improving even though the incidence of ectopic pregnancies is also increasing. The major reason for a poor outcome is a failure to seek early medical attention. Ectopic pregnancy remains the leading cause of pregnancy-related death in the first trimester of pregnancy.
In rare cases, an ectopic pregnancy may occur at the same time as intrauterine pregnancy. This is referred to as heterotopic pregnancy. The incidence of heterotopic pregnancy has risen in recent years due to the increasing use of IVF (in vitro fertilization) and other assisted reproductive technologies (ARTs).
What does an ectopic pregnancy look like?
For additional diagrams and photos, please see the last reference listed below.
What are the early and later signs and symptoms of ectopic pregnancy?
The woman may not be aware that she is pregnant. The three classic signs and symptoms of ectopic pregnancy include abdominal pain, the absence of menstrual periods (amenorrhea), and vaginal bleeding or intermittent bleeding (spotting). However, about 50% of females with an ectopic pregnancy will not have all three signs. These characteristic symptoms occur in ruptured ectopic pregnancies (those accompanied by severe internal bleeding) and non-ruptured ectopic pregnancies. However, while these symptoms are typical for an ectopic pregnancy, they do not mean an ectopic pregnancy is necessarily present and could represent other conditions. In fact, these symptoms also occur with a threatened abortion (miscarriage) in non-ectopic pregnancies.
The signs and symptoms of an ectopic pregnancy typically occur six to eight weeks after the last normal menstrual period, but they may occur later if the ectopic pregnancy is not located in the Fallopian tube. Other symptoms of pregnancy (for example, nausea and breast discomfort, etc.) may also be present in ectopic pregnancy. Weakness, dizziness and a sense of passing out upon standing can (also termed near-syncope) be signs of serious internal bleeding and low blood pressure from a ruptured ectopic pregnancy and require immediate medical attention. Unfortunately, some women with a bleeding ectopic pregnancy do not recognize they have symptoms of ectopic pregnancy. Their diagnosis is delayed until the woman shows signs of shock (for example, low blood pressure, weak and rapid pulse, pale skin, and confusion) and often is brought to an emergency department. This situation is a medical emergency.
What are risk factors for ectopic pregnancy?
Age: Ectopic pregnancy can occur in any woman, of any age, who is ovulating and is sexually active with a male partner. The highest likelihood of ectopic pregnancy occurs in women aged 35-44 years.
History: The greatest risk factor for an ectopic pregnancy is a prior history of an ectopic pregnancy.
Fallopian tube abnormalities: Any disruption of the normal architecture of the Fallopian tubes can be a risk factor for a tubal pregnancy or ectopic pregnancy in other locations.
Previous gynecological surgeries: Previous surgery on the Fallopian tubes such as tubal sterilization or reconstructive, procedures can lead to scarring and disruption of the normal anatomy of the tubes and increases the risk of an ectopic pregnancy.
Infections: Infection in the pelvis (pelvic inflammatory disease) is another risk factor for ectopic pregnancy. Pelvic infections are usually caused by sexually-transmitted organisms, such as Chlamydia or N. gonorrhoeae, the bacteria that cause gonorrhea. However, non-sexually transmitted bacteria can also cause pelvic infection and increase the risk of an ectopic pregnancy. The infection causes an ectopic pregnancy by damaging or obstructing the Fallopian tubes. Normally, the inner lining of the Fallopian tubes is coated with small hair-like projections called cilia. These cilia are important to transport the egg smoothly from the ovary through the Fallopian tube and into the uterus. If these cilia are damaged by infection, egg transport becomes disrupted. The fertilized egg can settle in the Fallopian tube without reaching the uterus, thus becoming an ectopic pregnancy. Likewise, infection-related scarring and partial blockage of the Fallopian tubes can also prevent the egg from reaching the uterus.
Multiple sex partners: Because having multiple sexual partners increases a woman's risk of pelvic infections, multiple sexual partners also are associated with an increased risk of ectopic pregnancy.
Gynecological conditions: Like pelvic infections, conditions such as endometriosis, fibroid tumors, or pelvic scar tissue (pelvic adhesions), can narrow the Fallopian tubes and disrupt egg transportation, thereby increasing the chances of an ectopic pregnancy.
IUD use: Approximately half of the pregnancies in women using intrauterine devices (IUDs) will be located outside of the uterus. However, the total number of women becoming pregnant while using IUDs is extremely low. Therefore, the overall number of ectopic pregnancies related to IUDs is very low.
Cigarette smoking: Cigarette smoking around the time of conception has also been associated with an increased risk of ectopic pregnancy. This risk was observed to be dose-dependent, which means that the risk is dependent upon the individual woman's habits and increases with the number of cigarettes smoked.
Infertility: A history of infertility for two or more years also is associated with an increased risk of ectopic pregnancy.
Other causes: Infection, congenital abnormalities, or tumors of the Fallopian tubes can increase a woman's risk of having an ectopic pregnancy.
Is there a test to diagnose ectopic pregnancy?
The first step in the diagnosis is an interview and examination by the doctor. The usual second step is to obtain a qualitative (positive or negative for pregnancy) or quantitative (measures hormone levels) pregnancy test. Occasionally, the doctor may feel a tender mass during the pelvic examination. If an ectopic pregnancy is suspected, the combination of blood hormone pregnancy tests and pelvic ultrasound can usually help to establish the diagnosis. Transvaginal ultrasound is the most useful test to visualize an ectopic pregnancy. In this test, an ultrasound probe is inserted into the vagina, and pelvic images are visible on a monitor. Transvaginal ultrasound can reveal the gestational sac in either a normal (intrauterine) pregnancy or an ectopic pregnancy, but often the findings are not conclusive. Rather than a gestational sac containing a visible embryo, the examination may simply reveal a mass in the area of the Fallopian tubes or elsewhere that is suggestive of, but not conclusive for, an ectopic pregnancy. The ultrasound can also demonstrate the absence of pregnancy within the uterus.
Pregnancy tests are designed to detect specific hormones the beta subunit of human chorionic gonadotrophin (beta HCG) blood levels are also used in the diagnosis of ectopic pregnancy. Beta HCG levels normally rise during pregnancy. An abnormal pattern in the rise of this hormone can be a clue to the presence of an ectopic pregnancy. In rare cases, laparoscopy may be needed to confirm a diagnosis of ectopic pregnancy. During laparoscopy, viewing instruments are inserted through small incisions in the abdominal wall to visualize the structures in the abdomen and pelvis, thereby revealing the site of the ectopic pregnancy.
Overview of Potential Agents of Biological Terrorism
"Infectious Disease is one of the great tragedies of living things - the struggle for existence between different forms of life . . Incessantly the pitiless war goes on, without quarter or armistice - a nationalism of species against species." Hans Zinsser- Rats, Lice and History (1934)
Infectious Agents as Tools of Mass Casualties
Historically, outbreaks (wars) of microbial species against the human species have killed far more people than war itself. Examples include i) killing of 95% of Pre-Columbian Native American populations by diseases like small pox, measles, plague, typhoid and influenza ii) death of 25 million Europeans (a quarter of the population) caused by Bubonic Plague in the 14th century and 21 million deaths due to the influenza pandemic of 1918-1919 (1).Worldwide, naturally occurring infectious diseases remain the major causes of death. In the United States, the impact of a number of very virulent biological agents and/or their toxins has been drastically reduced because of a very accessible health care system and excellent public health infrastructure. Still, a substantial number of people (approximately 70,000) die each year from infectious diseases (2). The travel and trade necessary for economic globalization, continued potential for transmission of infectious agents from animals to humans, and large populations living in proximity in major urban areas of the world, make disease outbreaks a major threat. The resistance of common pathogens to the available antimicrobial agents adds significantly to the threat. Advances in public health, diagnostic and pharmacological interventions are needed to protect the population from emerging and re-emerging infectious diseases. The global nature of infectious disease threats is well described in a statement prepared by Dr. David L. Heymann, Executive Director for Communicable Diseases, World Health Organization. This statement was presented to the Committee on Foreign Relations, United States Senate, during a hearing on "The Threat of Bioterrorism and the Spread of Infectious Diseases" on September 5, 2001 (3).
Bioterrorism , National Security and Law
Bioterrorism has now been defined as the intentional use of a pathogen or biological product to cause harm to a human, animal, plant or other living organisms to influence the conduct of government or to intimidate or coerce a civilian population(4). Biological agents are easy to develop as weapons, are more lethal than chemical weapons, are less expensive and more difficult to detect than nuclear weapons (5). Diseases caused by biological agents are not only a public health issue but also a problem of national security. Two simulated biological attacks, Dark Winter (small pox) and TOPOFF (plague), in the United States demonstrated serious weaknesses in the public health system that could prevent an effective response to bioterrorism or severe naturally occurring infectious diseases (6,7,8,9,10). The intentional dispersal of anthrax through the United States Postal Service that followed the terrorist attacks of September 11, 2001, brought these issues into a clear focus. The United States government began a process to strengthen the public health infrastructure. The need for law reform was recognized as law has long been considered as an important tool of public health (11). The power to act to preserve the Public's Health is constitutionally reserved primarily to the states as an exercise of their police powers. Some states like Colorado and Rhode Island had developed legislation or administrative public health plans for a bioterrorism event prior to September 1, 2001. The Model Act was designed to update and modernize the state public statutes and to avoid problems of inconsistency, inadequacy and obsolescence. The Model State Emergency Health Powers Act (MSEHPA or Model Act) was drafted by the Center for Law and the Public's Health at Georgetown and Johns Hopkins Universities at the request of the Centers for Disease Control and Prevention (CDC) and in collaboration with members of national organizations representing governors, legislators, attorneys general and health commissioners (4,12). This act provides state actors with the powers to detect and contain bioterrorism or a naturally occurring disease outbreak. The Model Act is structured to facilitate five basic public health functions i) Preparedness, comprehensive planning for a Public Health emergency ii) Surveillance, measures to detect and track Public Health emergencies iii) Management of Property, ensuring adequate availability of vaccines, pharmaceuticals and hospitals as well as providing power to abate hazards to the Public's Health iv) Protection of Persons, powers to compel vaccination, testing, treatment, isolation and quarantine when clearly necessary and v) Communication, providing clear and authoritative information to the public. The act also contains a modernized, extensive set of principles and requirements to safeguard personal rights. Based on MSEHPA, legislative bills have been introduced in 34 states and the District of Columbia. As of June 26, 2002, 16 states and the District of Columbia already have enacted a version of the act and the states enacting or expected shortly to enact legislation, influenced by the Model Act were Arizona, Florida, Georgia, Hawaii, Maine, Maryland, Minnesota, Missouri, New Hampshire, New Mexico, Oklahoma, South Carolina, South Dakota, Tennessee, Utah and Virginia.
The Model State Emergency Health Powers Act (MSEHPA)
Reprinted JAMA, August 7, 2002, Vol 288 No. 5 Page 625-628
A critique of the Model State Emergency Health Powers Act was published by Annas G. In Bioterrorism, Public Health and Civil Liberties. NEJM, 2002 April 24:346(13) At the federal level, Public Health Security and Bioterrorism Preparedness and Response Act of 2002, HR 3448, was passed by the United States Congress on May 23, 2002 and signed into law (Public Law 107-188) June 12, 2002. The bill is intended to improve the health system's ability to respond to bioterrorism, protect the nation's food supply and drinking water from bioterrorist attacks, speed the development and production of new drug treatments and vaccines, address shortages of specific types of health professions, improve coordination of federal anti-bioterrorism activities, increase investment in federal, state, and local preparedness and expand controls over the most dangerous biological agents and toxins. The American Society for Microbiology (ASM) has testified before congress on issues surrounding biosecurity and has worked closely with congress in the drafting of Title II to balance Public Health concern over safely and security with need to protect legitimate scientific research and diagnostic testing. Important new provisions for the possession, use and transfer of select agents, (42 biological agents and toxins listed in Appendix A of 42 CFR part 72), are included in Title II of HR 3448, Enhancing Controls on Dangerous Biological Agents and Toxins. On July 12, 2002, the CDC announced preliminary guidance for notification of possession of select agents as mandated in Section 202 (a) of Public Law 107-188, the Public Health Security and Bioterrorism Preparedness and Response Act of 2002 (Appendix B). The notice states that each facility should designate a responsible facility official (RFO) to complete the notification of possession form by September 10, 2002. The RFO will need to inventory the facility and consult with others (e.g. Principal Investigators) to obtain the required information. At our institution a Designated Safety Officer in collaboration with the Infection Control and Safety Committee address these issues. In order to avoid inconsistencies and noncompliance, at the July meeting, it was recommended to the Committee that the Principal Investigators provide a complete list of all the biological agents being used in their laboratories. The Safety Officer would then use the information needed to register with the Secretary of Health and Human Services and provide inspections to ensure safety and compliance with the requirements.
Historical Perspective and Trends Related to Bioterrorism
The intentional use of living organisms or infected materials derived from them has occurred over centuries during war and "peace" time by armies, states, groups and individuals (14,15,16). One of the first recorded uses of a biological agent in the war was in 184 BC. The Carthaginian soldiers led by Hannibal used snakes in the battle against King Eumenes of Perganium and achieved a victory (17,18). As early as 300 BC, the Greeks polluted the wells and drinking water supplies of their enemies with animal corpses. The use of catapults and siege machines introduced new technology to biological warfare. Some of the more recent events of biological warfare are chronicled below -
The Tartars catapulted bodies infected with plague into Caffa (now Ukraine) in 1346 at the end of a 3 day siege.
The inhabitants of Central and South America were decimated by small pox and measles that accompanied the Spanish conquistadors.
British forces used blankets contaminated with small pox to infect North American Indians in the 18th century.
The modern era of biological weapons development began immediately before and during World War II. The Japanese released fleas infected with plague in Chinese cities in the 1930's and 1940's. Between 1940 and 1942 Japanese unit 731 dropped bombs containing up to 15 million plague infected fleas on two Chinese cities - Quxian and Ning-hsien, resulting in at least 120 deaths. Water supplies and food items were contaminated with B. anthracis, V. Cholera, Shigella spp., Salmonella and Yersinia pestis.
Weather Underground (1970), a United States revolutionary group intended to obtain agents at Ft. Detrick by blackmail and to temporarily incapacitate United States cities to demonstrate the impotence of the federal government. Report originated with a US Customs informant.
R.I.S.E. (1972). College students influenced by ecoterrorist idealogy and 1960's drug culture planned on using agents of typhoid fever, diphtheria, dysentery and meningitis to target the entire world population initially and later narrowed the plan to five cities near Chicago. The attack was aborted when cultures were discarded.
Bulgarian defector Georgi Markov was assassinated in Lauda (1978) using ricin-filled pellet infected with a spring-loaded device disguised in an umbrella. Similar device used against a second defector in the same area was unsuccessful.
Sverdlovsk, Russia (1979). Accidental release of anthrax from Soviet bioweapons facility caused an epidemic of inhalational anthrax with at least 77 cases and 60 deaths.
Red Army Faction (1980). Members of a Marxist revolutionary ideology group allegedly cultivated botulinum toxin in a Paris safe-house and planned attacks against at least 9 German officials and civilian leaders. This probably was an erroneous report, later repudiated by the German government.
Rajneeshee Cult (1984). Indian religious cult headed by Rajneeshee plotted to contaminate restaurant salad bars with Salmonella typhimanice in Dallas, Oregon. The motivation was to incapacitate voters to win local elections and seize political control of the county. The incident resulted in a large community outbreak of salmonellosis involving 751 patients and at least 45 hospitalizations. The plot was revealed when the cult collapsed and members turned informants.
Minnesota Patriots Council (1991). Right wing "Patriot" movement obtained Ricin extracted from castor beans by mail order. They planned to deliver ricin through skin with DMSO and aloe vera or as dry aerosol against IRS officials, US Deputy Marshals and local law enforcement officials. Group was penetrated by Federal Bureau of Investigation (FBI) informants.
Aum Shinrikyo (1995). New Age Doomsday cult seeking to establish a theocratic state in Japan attempted at least 10 times to use anthrax, botulinum toxin, Q fever agent and Ebola virus in aerosol form. All attempts with biological weapons failed. Multiple chemical weapon attacks with Sarin, Vx, hydrogen cyanide in Matsumato, Tokyo and an assassination campaign were conducted. Nerve gas Sarin killed 12 and injured 5500 in Tokyo subway.
Texas (1997). Intentional contamination of muffins and donuts with laboratory cultures of Shigella dysenteriae. The event caused gastroenteritis in 45 laboratory workers and 4 were hospitalized.
Larry Wayne Harris (1998). Allegedly threatened to release "military grade anthrax" in Las Vegas, Nevada. Obtained plague and anthrax (vaccine strains), repeatedly isolated several other bacteria. Made vague threats against US federal officials on behalf of right wing "patriot" groups. Arrested when he talked openly about biological weapons terrorism.
Unknown individual/group (2001). Intentional dissemination of anthrax spores through the US Postal System leading to the death of five people, infection of 22 others and contamination of several government buildings. Investigation into the attacks so far has not led to any conclusions.
Chronology of Anti-Bioterrorism (Biosafety) Actions (19).
1910 - 1920's The fist use of chemical and biological weapons in combat leads to efforts to ban their use.
1925 The Geneva Protocol prohibits the use of biological and chemical weapons in war. The United States signs but fails to ratify the treaty. The treaty contained no provision for verifications and inspection.
1950's - 1970's The Soviet Union and United States build arsenals of biological and chemical weapons. International pressures mount to draw up new treaties to curb such weapons.
November 25, 1969 President Richard M. Nixon unilaterally renounces the use of biological weapons in war by the United States and restricts research to immunization and safety efforts. Three months later, he extends the ban to include toxins.
1972 Convention on the prohibition of the development, production, and stockpiling of bacteriological (biological) and toxin weapons and their destruction opened for signature at Washington, London, and Moscow on April 10, 1972.
1975 The United States ratifies the Biological and Toxin Weapons Convention as well as the 1925 Geneva Protocol on January 22, 1975. The Biological and Toxin weapons Convention entered into force March 26, 1975. There are now 143 states parties to the convention and an additional 18 signatories (20). Article VI of the Convention that provides for actions against noncompliance has proved to be an inadequate mechanism.
1980's Arms control initiatives fail to curb biological and chemical weapons proliferation.
1984 The Reagan administration presented a draft treaty to ban the production and storage of chemical weapons to the Conference on Disarmament in Geneva.
1990's Concerns over exposure to chemical and biological weapons during the Persian Gulf War increased support for international treaties.
May 13, 1991 Shortly after the Allied victory against Iraq, President George Bush announced that the United States will renounce the use of chemical weapons for any reason . . . an international treaty banning them takes effect.
April, 1992 Russian President Boris N. Yeltsin declares that Russia's biological weapons program is being discontinued..
January, 1993 President George Bush signs the Chemical Weapons treaty at the convention banning the production and use of chemical weapons.
January 7, 1997 The Presidential Advisory Committee on Gulf War Veterans' illnesses, finds no conclusive evidence linking Gulf War Syndrome to exposure to chemical or biological weapons.
April 15, 1997 New regulations aimed at limiting access to chemicals and pathogens that could be made into weapons go into effect under the 1996 Antiterrorism and Effective Death Penalty Act.
April 29, 1997 The Chemical Weapons Convention went into effect. It has more than 160 signatories and 65 ratifications.
July 25, 2001 The United States rejected a protocol to strengthen the Biological Weapons Convention as well as the whole approach to it (21). Like the Chemical Weapons Conventions (CWC), a strong bioweapons protocol could add to the deterrence of bioweapons which are a much greater threat.
November 19, 2001 Fifth BWC Review Conference
Potential Biological Weapons Threat Repositories and Sources
The origin of the biological weapons program of the former Soviet Union dates back to statements by Lenin. Although experimental work was started in the late 1920's, the modern era was ushered in only with the postwar military building programs (22). The Allied Biological Weapons program had shifted from the British research into anthrax (and the development of the World War II anthrax cattlecake retaliation weapon), to a large United States based research, development and production capability. The United States military had accepted seven types of classified agents and could produce 650 tons of an agent per month at plants such as the one at Pine Bluff in Arkansas. This offensive program was unilaterally abandoned in 1969, giving impetus to the creation of the Biological and Toxin Weapons Convention. The Soviet Union signed the Convention at its inception in 1972. Unfortunately, the number of countries engaged in biological weapons experimentation has grown from 4 in the 1960's to 11 in the 1990's (23). It is estimated that at least 10 nations and possibly 17 possess biological warfare agents (24) . Of the seven countries listed by the United States Department of State as sponsoring international terrorism, at least five are suspected to have biological warfare programs (25). Nations and dissident groups have the access to skills needed to selectively cultivate some of the most dangerous pathogens and to deploy them as agents of biological terrorism and war (26).
The Japanese cult Aum Shinrikyo that released the nerve gas Sarin in the Tokyo subway also had plans for biological terrorism (27). They were in possession of large quantities of nutrient media, botulinum toxin, anthrax cultures and drove aircraft equipped with spray tanks. Members of this group had traveled to Zaire in 1992 to obtain samples of Ebola virus. Aum Shinrikyo is an example of a large well financed organization that was attempting to develop biological weapons capability. Such organizations would be expected to cause the greatest harm, because of their access to scientific expertise, biological agents and most importantly, dissemination technology (28).
Smaller, less sophisticated organizations may use biological agents to further their specific goals rather than to kill. Such organizations could use readily available pathogens. The Rajhneeshees who attempted to influence local elections in Dallas, Oregon by contaminating salad bars with Salmonella typhimurium .
The third type are smaller groups or individuals who may have very limited targets, e.g. individuals or buildings. The likelihood of events related to such use is high but the public health consequences are low. As of now, the use of anthrax spores through the United States postal system seems to be an example of this type of biological terrorism. Iraq's biological weapons program dates back to at least 1974 and has been carried out secretly after the Biological and Toxin Weapons Convention had been signed. In 1995, Iraq confirmed that it had produced and deployed bombs, rockets and aircraft spray tanks containing Bacillus anthracis and botulinum toxin (29). In 1973 and 1974, the Soviet Politburo formed the organization known most recently as Biopreparat designed to carry out offensive biological weapons programs concealed behind civil biotechnology research (22). Concepts of use had been developed for each of the biological agents formally accepted by the army. In January 1991, the first ever visit to Biopreparat facilities was undertaken by a Joint United Kingdom/United States technical team. By the mid 1990's substantial changes took place within Biopreparat and a concerted effort is underway to help the Russians civilianize these former biological weapons research and development establishments. The current capability of the old Russian Ministry of Defense sites remains largely unknown. The status of one of Russia's largest and most sophisticated former bioweapons facilities, called Vector in Koltsovo, Novosibirsk is of concern. The facility housed the small pox virus as well as work on Ebola, Marburg and the hemorrhagic fever viruses (e.g., Machupo and Crimean-Congo) (26). A visit in 1997 found a half-empty facility protected by a handful of guards. No one is clear where the scientists have gone. The confidence that this is the only storage site for small pox outside the Centers for Diseases Control and Prevention is lacking.
The Threat of Biological Weapons
The Biological weapons system is comprised of four components a payload, munition, delivery system and dispersion system. The payload is the biological agent itself. The munition protects and carries the payload to maintain its potency during delivery. The delivery system can be a missile, vehicle (aircraft, boat, automobile or truck), or an artillery shell. The dispersion system ensures dissemination of the payload at the target site. Potential methods of dispersion are aerosol sprays, explosives, and food or water contamination. Aerosol sprays are the most effective means of widespread dissemination. Depending on atmospheric conditions and the agent itself, infectious material could travel several hundred kilometers in a particle size that upon inhalation would be delivered to the terminal airways. However factors like particle size of the agent, stability of the agent under desiccating conditions and ultraviolet light, wind speed, wind direction, and atmospheric stability can alter the effectiveness of a given delivery system. Explosions are likely to inactivate biological agents and therefore are not very effective in disseminating infectious materials. Contamination of water supplies generally requires an addition of an unrealistically large amount of biological agent(s) to a city supply. The agents may be introduced into smaller reservoirs or into the water supply after the water passes through its purification facility. Food supplies are easier to contaminate than water supplies. The outbreaks from food source may be dismissed as a "natural" event early during a bioterrorism attack (30, 31).
For a biological weapon to be highly effective, three conditions should be optimized. The biological agent should consistently produce the desired effect of death or disease. It should be highly contagious with short and predictable incubation period and infective in low doses. The disease should be difficult to identify and be suspected as an act of bioterrorism. The agents should be suitable for mass production, storage, weaponisation, and stable during dissemination. The target population should have little or no immunity and little or no access to treatment. The terrorist should have means to protect or treat their own forces and population against the infectious agents or the toxins (32).
The agents with potential of biological terrorism include bacterial, fungal and viral pathogens and toxins produced by living organisms. Infectious agents that could potentially be used include those causing anthrax (Bacillus anthracis), plague (Yersinia pestis), tularemia (Francisella tularensis), equine encephalitides (e.g. Venezuelan equine encephalitis viruses), hemorrhagic fevers (arenaviruses, filoviruses, flaviviruses, and bunyaviruses), and small pox (variola virus). Toxins include botulinum toxin from Clostridium botulinum ricin toxin from the castor bean Ricinus communis trichothecene mycotoxins from Fusarium, Myrotecium Trichoderma, Stachybotrys, and other filamentous fungi staphylococcal enterotoxins from Staphylococcus aureus and toxins from marine organisms such as dinoflagellates, shellfish, and blue-green algae. Depending on the agents, a lethal or incapacitating outcome can occur. In a military context, incapacitating agents may be more effective because the unit will not be able to perform their mission and casualties will consume scarce medical and evacuation assets (31).
Biological weapons are very attractive to the terrorist because of several characteristics. Aerosols of biological agents are invisible, silent, odorless, tasteless, and are relatively easily dispersed. They are 600 - 2000 times cheaper than other weapons of mass destruction. It is estimated that the cost would be about 0.05% the cost of a conventional weapon to produce similar numbers of mass casualties per square kilometer. The production is relatively easy, using the common technology available for the production of some antibiotics, vaccines, foods, and beverages. The delivery systems such as spray devices from an airplane, boat or car are commonly available. The natural lead time provided by the organism's incubation period (3 to 7 days for most potential organisms) would allow for the terrorists' escape before any investigation starts. In addition, the use of an endemic infectious agent may cause confusion because of the inability to differentiate a biological warfare attack from a natural epidemic. For some agents potential exists for secondary or tertiary transmission by person-to-person transmission or natural vectors.
The consequences of biological weapons use are many. They can rapidly produce mass effect that overwhelms services and the health care system of the communities. Most of the civilian population is susceptible to infections caused by these agents. They are associated with high morbidity and mortality rates. The resulting illness is usually difficult to diagnose and treat early, particularly in areas where the disease is rarely seen. One kilogram of anthrax powder has the capability to kill up to 100,000 people depending on the mechanism of delivery (33). The economic impact of a biological attack has been estimated to be from 478 million/100,000 persons exposed (brucellosis scenario) to 26.2 billion/100,000 persons exposed (anthrax scenario) (34).
Types of Bioterrorism Attacks
A bioterrorist attack may occur in 2 scenarios - overt and covert. In the past emergency responses were prepared based on overt attacks like bombings and chemical agents that cause immediate and obvious effects. However, attacks with biological agents are more likely to be covert. They pose different challenges and require emergency planning with the involvement of the public health infrastructure. The attack by a biological agent will not have an immediate impact because of the delay between exposure and onset of illness (i.e., the incubation period). Therefore, the first victims of a bioterrorism action will need to be identified by physicians or other primary health care providers. Based on the first wave of victims, pubic health officials will need to determine that an attack has occurred, identify the organism and prevent more casualties through prevention strategies (e.g. mass vaccination, prophylactic treatment) and infection control procedures (35). The clues to a potential bioterrorist attack include an outbreak of a rare or new disease, an outbreak of diseases in a non-endemic area, a seasonal disease during an off season time, a known pathogen with unusual resistance or unusual epidemiologic features, an unusual clinical presentation or age distribution, a genetically identical pathogen emerging rapidly in different geographical areas (36).
Agents of Bioterrorism Attacks
Based on the ease of transmission, severity of morbidity, mortality, and likelihood of use, biological agents can be classified into 3 categories (Table 1) (35). Table 2 summarizes the biological agents in category A.
Category A Agents
Category A includes the highest priority agents that pose a risk to national security because of the following features -
i). They can be easily disseminated or transmitted person-to-person causing secondary and tertiary cases.
ii) They cause high mortality with potential for major public health impact including the impact on health care facilities.
iii) They may cause public panic and social disruption.
iv) They require special action for public health preparedness.
Anthrax, Botulism, Tularemia, small pox and viral hemorrhagic fever will be discussed in detail during the workshop. In addition, we will have two general presentations - one on laboratory diagnosis of biological weapons and the other the care of children in the event of biological terrorism.
In this presentation, I will discuss Plague as a disease and Yersinia pestis as a potential agent of bioterrorism followed by and overview of Category B and Category C weapons.
Microbiology and Epidemiology
Plague is caused by Yersinia pestis, previously called Pasturella pestis. Yersinia pestis is a nonmotile, nonsporulating, bipolar-staining, gram-negative coccobacillus in the genus Yersinia and the family Enterobacteriaceae. It is microaerophilic, indole, oxidase- and urease-negative non-lactose fermenting and biochemically unreactive. It grows aerobically on most culture media, including blood agar and MacConkey agar. Plague is a notorious cause of catastrophic epidemics. Epidemic bubonic plague was vividly described in biblical and medieval times. This disease was estimated to have killed one fourth of Europe's population in the Middle Ages. The most recent pandemic originated in China and spread worldwide at the turn of the 20th century. Large outbreaks of pneumonic plague occurred in Manchuria and India during 1910 - 1911, and 1920 and 1921. During World War II, Japan investigated the use of plague as a biological weapon. The United States studied Y. pestis as a potential agent in the 1950's before the offensive BW program was terminated, and other countries have been suspected of weaponizing plague.
Y. pestis is maintained in nature as a zoonotic infection in rodent hosts and their fleas in large areas of Asia, Africa and the Americas. Transmission to humans occurs by contact with fleas and respiratory droplets from animals or infected humans. In naturally occurring plague, the bite by an infected flea leads to the inoculation of thousands of organisms into a patient's skin. The bacteria migrate through cutaneous lymphatics to regional lymph nodes where they are phagocytosed but not killed. They rapidly multiply in the lymph nodes with subsequent bacteremia, septicemia, and endotoxemia that can lead quickly to shock, disseminated intravascular coagulation, and coma.
The three major forms of Y. Pestis infection in humans are classical bubonic plague, primary septicemic plague and pneumonic plague, accounting for 84, 13 and 2% respectively, of cases reported in the United States from, 1947 to 1996 (37). Patients typically develop symptoms of bubonic plague 2 to 8 days after an infected flea bite. Systemic symptoms include fever, chills, weakness, and headache followed by the development of an acutely swollen lymph node or bubo within a day. The painful bubo commonly develops in the groin, axilla or cervical region and the overlying skin is erythematous. They are extremely tender, nonfluctuant, and warm with surrounding edema but no lymphangitis.
A distinctive feature of plague, in addition to the bubo, is the propensity of the disease to overwhelm the patient with a massive growth of bacteria in the blood. In the early acute stages of bubonic plague, all patients probably have intermittent bacteremia. Occasionally in the pathogenesis of plague infection, bacteria are inoculated and proliferate in the body without producing a bubo. Patients become ill with fever and actually die with bacteremia but without detectable lymphadenitis. This syndrome has been termed Primary Septicemic Plague to denote plague without a bubo. Septicemia can also occur secondary to bubonic plague. Septicemic plague leads to disseminated intravascular coagulation, necrosis of small vessels, and purpuric skin lesions. Gangrene of acral regions such as the digits and nose may also occur in advanced disease. This clinical presentation is believed to be responsible for the name "black death" in the second plague pandemic.
Primary pneumonic plague resulting from the inhalation of plague bacilli occurs rarely in the United States. Reports of two recent cases of primary pneumonic plague, contracted after handling cats with pneumonic plague, reveal that both patients had respiratory symptoms as well as prominent gastrointestinal symptoms including nausea, vomiting, abdominal pain, and diarrhea. Both patients died because of delayed diagnosis and treatment (38,39).
Secondary pneumonic plague develops in a minority of patients with bubonic or primary septicemic plague - about 12% of total cases in the United States over the past 50 years (40). The infection reaches the lungs by hematogenous spread of bacteria from the bubo. In addition to the high mortality rate, plague pneumonia is highly contagious by airborne transmission. It manifests in the setting of fever and lymphadenopathy with cough, chest pain, and often hemoptysis. Radiographically, there is patchy bronchopneumonia, cavities, or confluent consolidation (32). The sputum is usually purulent and contains plague bacilli.
The epidemiology, pathogenesis and clinical manifestations of plague following a biological attack may be different than naturally occurring plague. Primary pneumonic plague due to inhaled aerosolized Y. pestis bacilli would be most likely. The time from exposure to aerosolized Y. pestis to the development of the first symptoms in humans and nonhuman primates has been found to 1 to 6 days. The first signs of illness would be fever with cough and dyspnea, sometimes with the production of bloody, watery purulent sputum. Prominent gastrointestinal symptoms, including nausea, vomiting, abdominal pain, and diarrhea, might be present adding to diagnostic difficulty (37). The absence of buboes would differentiate primary from secondary pneumonic plague. Patients diagnosed with pneumonic plague should be housed under respiratory droplet precautions. Additionally, standard cleaning and disinfection guidelines should be followed for objects and clothing contaminated with the blood and body fluids.
Laboratory Diagnosis
A high index of clinical suspicion and a careful clinical and epidemiologic history and physical examination are required to allow timely diagnosis of plague. When plague is suspected, specimens should be obtained promptly for microbiological studies and specific antimicrobial therapy should be initiated pending confirmation. Appropriate diagnostic specimens for smear and culture include blood in all patients, lymph node aspirates in those with suspected buboes, sputum samples or tracheal aspirates in those with suspected pneumonic plagues, and cerebrospinal fluid in those with suspected meningitis. If possible, the specimens should also be examined using direct flourescent antibody (DFA) testing. An acute phase serum should be collected for Y. pestis antibody testing, followed by a convalescent phase specimen collected 3 to 4 weeks later.
For the Level A laboratory at a community hospital, the presence of small gram-negative coccobacilli with a safety pin appearance (seen more clearly on Wright-Giemsa rather than gram stain) from blood, lymph node aspirate or respiratory secretions from a patient with a short history of fever and lymphadenopathy should raise the suspicion of Y. pestis. The specimen should be submitted to the nearest Level B or C laboratory (36). Cultures demonstrate growth at 24 - 48 hours of incubation at 37OC. Automated or semiautomated systems may misidentify Y. pestis and laboratories without automated systems may take 4 - 6 days to suspect the organism. At the Level B laboratories, identification can be confirmed by a direct fluorescent antibody test to detect the fraction 1 (F1) envelope antigen of Y. pestis. This antigen is expressed only at 37OC after 24 to 48 hours incubation. These laboratories can do in vitro antimicrobial susceptibility testing by e-test, complete biochemical confirmation and specific phase lysis tests for Y. pestis. Enzyme immunoassay, passive hemagglutination and passive hemagglutination inhibition tests can be done to detect antibody to F1 antigen. Rapid diagnostic tests like antigen detection, IgM enzyme immunoassay, immunostaining and polymerase chain reaction are available only at some state health departments, CDC and the military laboratories.
Antimicrobial Therapy.
There is a lack of clinical trials in treating plague in humans for a number of reasons including the requirement for a large number of patients. The working group on Civilian Biodefense has made recommendations based on the best available evidence in collaboration with scientists from a number of federal agencies (37). Primary pulmonary plague during the past 50 years in the United States has had a fatality rate of 57%. The fatality rate is extremely high when treatment is delayed more than 24 hours after symptom onset. Streptomycin is the FDA approved antibiotic for plague and is responsible for reducing overall plague mortality to 5 to 14%. Gentamicin is an acceptable alternative. Gentamicin is more widely available than streptomycin and has shown equal or better activity in in vitro and in animal studies.
Tetracycline and doxycycline are also FDA approved for treatment and prophylaxis of plague. In vitro activity of tetracycline and doxycycline against Y. pestis is equivalent to that of aminoglycosides. Experimental murine models have yielded data difficult to extrapolate to humans. F1 deficient variants have decreased susceptibility to doxycycline. There are no controlled clinical trials comparing tetracycline or doxycycline to aminoglycosides in the treatment of plague. The working group recommends that the tetracycline class of antibiotics be used to treat pneumonic plague if aminoglycosides cannot be used. Doxycycline should be considered pharmacologically superior to other agents in the class. Fluoroquinolones have demonstrated efficacy in animal studies and in vitro studies comparable to that of aminoglycosides and tetracyclines. Chloramphenicol has been recommended for treatment of plague meningitis but no clinical trials have been done. Trimethoprin/Sulfamethoxacole has been considered a second tier choice while others have recommended sulfonamides only for pediatric prophylaxis. Rifampin, Aztreonam, Ceftazidime, Cefotetan and Cefazolin have shown poor efficacy in animal studies. Resistance of Y. pestis to tetracycline class of drugs has been reported recently and Russian scientists have published a report of quinolone resistance. A multidrug resistant strain (plasmid mediated) was isolated in Madagascar (42).
Post Exposure Prophylaxis
Close contact for purposes of initiating antimicrobial prophylaxis is defined as contact with a patient at less than 2 meters. Asymptomatic persons having close household, hospital or other close contact should receive post exposure prophylaxis for 7 days. Tetracycline, doxycycline, sulfonamides and chloramphenicol have each been used or recommended for prophylaxis in this setting. The working group recommends doxycycline as the first choice for post exposure prophylaxis.
A licensed killed whole cell vaccine was available in the United States from 1946 to late 1998. It offered protection against bubonic plague but did not prevent or ameliorate the development of primary pneumonic plague (43). Currently, a fusion protein vaccine (F1-V antigen) is in development at the United States Army Medical Research Institute of Infectious Diseases (44). It protected mice against an inhalational challenge for a year and is now being tested in primates.
Infection Control Procedures
Standard precautions should be used for bubonic plague patients. Suspected pneumonic plague cases require strict isolation with droplet precautions for 48 hours or longer after antibiotics are started or until sputum cultures are negative in confirmed cases. Pneumonic plague transmission was prevented in close contacts by wearing masks (37,44). In addition to a surgical mask, gown, gloves and eye protection are recommended for contact with a case of pneumonic plague. Patients being transported should also wear surgical masks. Patients can be cohorted while undergoing antibiotic therapy. Isolation of close contacts refusing antibiotic prophylaxis is not recommended. Hospital rooms of patients with pneumonic plague should receive terminal cleaning and contaminated clothing should be disinfected per hospital protocol (46). Bodies of patients who have died with plague should be handled with routine strict precautions (46). If aerosol generating procedures are necessary, high efficiency particulate air filtered masks and negative pressure rooms should be used. Microbiology laboratory personnel should be alerted when a diagnosis of plague is suspected. Routine microbiology procedures should be conducted at biosafety Level 2 conditions. For activities involving high potential for aerosol or droplet production (centrifugation, grinding, vigorous shaking and animal studies) biosafety Level 3 condition are necessary.
Y. pestis is far more susceptible to environmental conditions than sporulating bacteria such as Bacillus anthracis. It is very sensitive to sunlight and heat and does not survive long outside the host. In the worst case scenario analyzed by WHO, a plague aerosol was estimated to be effective and infectious for as long as 1 hour. In the setting of a terrorist release of Y. pestis, the aerosol would have dissipated long before the first case of pneumonic plague is recognized. Thus, there is no need for environmental decontamination of an area exposed to an aerosol of Y. pestis.
If vectors (fleas) and reservoirs (rodents) are present, measures must be taken to prevent the natural cycles for Y. pestis. Rodent control measures, flea insecticides and flea barriers for patient care areas are recommended.
Category B Agents
This category (47) contains the second highest priority agents because they
a. are moderately easy to disseminate
b. cause moderate morbidity and low mortality
c. require specific enhancement of CDC's diagnostic capacity and enhanced disease surveillance
Table 3 - Category B Bioterrorism Agents
Ricin toxin
(Ricinus communis)
Epsilon toxin
(Clostridium perfringens)
Enterotoxin B
(Staphylococccus aureus)
T2 - Mycotoxins*
*Not listed under CDC Category B agents
Food or Water Borne Pathogens
Salmonella species
Shigella dysenteria
Escherichia coli 0157:H7
Vibrio cholerae
Cryptosporidum parvuus
First described in Australia and called Q fever because the causative agent was unknown.
Epidemiology/Microbiology
Q fever is caused by Rickettsia , Coxiella burnetti is a world wide zoonosis (44,47,48). The most common reservoirs are cattle, sheep and goats. Other natural reservoirs are dogs, cats and birds. The infected animals do not develop the disease but shed large numbers of organisms in body fluids (milk, urine, and feces) and especially large numbers in the placenta. Humans acquire the disease by inhalation of contaminated aerosol. Q fever as a febrile illness with an atypical pneumonia can resemble mycoplasma, Legionnaire's Disease, Chlamydia pneumonia, psittacosis and Hantavirus infection. More rapidly progressive cases may resemble tularemia or plague. The organism is resistant to heat and desication and highly infectious by aerosol route. A single inhaled organism is capable of producing clinical illness. C. burnetti could be used as an incapacitating biological warfare agent and the disease would be similar to that occurring naturally.
Diagnosis -
The incubation period is 2 - 14 days, varies according to number of organisms inhaled. The disease presents as a self limiting acute febrile illness with headaches, fatigue and myalgias. Pneumonia, manifested by abnormal chest x-ray occurs in 50% of patients and acute hepatitis develops in 33% of patients. Culture negative endocarditis, chronic hepatitis, aseptic meningitis, encephalitis, and osteomyelitis are uncommon complications of Q fever.
Isolation of the organism is difficult. Antibody assay (IFA and ELISA and complement fixation tests) are available at reference laboratories. IgM antibodies may be detected by ELISA as early as the second week of illness and are diagnostic. Complement fixation test, the most commonly available serological test, is relatively insensitive.
Management -
All suspected cases of Q fever should be treated to reduce the risk of complications. Tetracycline or doxycycline or erythromycin for 5 - 7 days are the treatment of choice for Q fever. Azithromycin and Clarithromycin would be expected to be effective, although they have not been tested. Ciprofloxacin and other quinolones are active in vitro and should be used in patients unable to take the other agents. For endocarditis, tetracycline or doxycycline given in combination with TMP/SMX or rifampin for 12 months or longer has been successful in some cases. Valve replacement is often required for a cure.
Chemoprophylaxis with tetracycline or doxycycline for 5 - 7 days is effective if started 8 - 12 days post exposure. However, if given immediately (1-7 days) after exposure, chemoprophylaxis is not effective and may only prolong the onset of disease.
A formalin inactivated whole cell vaccine is licensed in Australia and available for at-risk personnel on an investigational basis in the United States. A single dose provides complete protection against naturally occurring Q fever and greater than 95% protection against aerosol exposure within 3 weeks. Protection lasts for at least 5 years. The vaccine may cause local induration, sterile abscess and even necrosis at the inoculation site in immune individuals. An intradermal skin test using 0.02 mg of specific formalin - killed whale cell vaccine is required to detect presensitized or immune individuals. A live attenuated vaccine (Strain M44) has been used in the former USSR. There is no person- to- person transmission of Q fever. Standard precautions are recommended for health care workers taking care of patients with suspicion or diagnosis of Q fever.
Also called undulant fever, Mediterranean Fever, Malta Fever
Epidemiology and Microbiology
Brucellosis is a zoonotic disease caused by infection with one of the six species of Brucellae, a group of facultative intracellular gram negative coccobacilli (36,44,49). The natural reservoir is herbivores like goats, sheep, cattle and pigs. Four species, B melitensis (goat), B. abortus (cattle), B. suis (pig), and B canis (dog) are pathogenic in humans. Human infection occurs by ingestion of raw infected meat or milk, inhalation of contaminated aerosols or through skin conduct. Brucellosis is highly infective by the aerosol route, with as few as 10 - 100 bacteria sufficient to cause disease in humans. Brucella sp. are stable to environmental conditions and there is a long persistence in wet ground or food. These features make them potential agents of bioterrorism. The disease is relatively prolonged, incapacitating, and disabling in its natural form. Intentional large aerosol doses may shorten the incubation period and increase the clinical attack rate. However, mortality rate (5% of untreated cases) is low with rare deaths caused by endocarditis or meningitis. Brucellosis became the first agent weaponized by the United States at Pine Bluff Arsenal in 1954, when its biological weapons program was active. Human brucellum is an uncommon disease in the United States. The annual incidence is 0.5 cases per 100,000 population. Most cases occur in abattior and veterinary workers or are associated with the ingestion of unpasteurized dairy products. The disease is still highly endemic in the southwest Area (128,000 cases per 100,00 population in some areas of Kuwait). This represents a hazard to military personnel in those areas.
The usual incubation period is 8 - 14 days but may be longer. Brucellosis presents as a nonspecific febrile illness with headache, fatigue, myalgias, chills, sweats and cough. Lumbar pain and tenderness can occur in up to 60% of cases. GI symptoms - anorexia, nausea, vomiting, diarrhea and constipation occur in up to 70% of adult cases, less frequently in children. Hepatosplenomegaly is seen in 45 - 63% of cases. The significant sequaelae include various osteoarticular infections of the axial skeleton, peripheral arthritis, granulomatous hepatitis, meningitis, encephalitis, peripheral neuropathy, meningovascular syndrome, optic neuritis, infective endocarditis, anemia, thrombocytopenia and leukopenia.
Blood cultures are positive in 15 - 70% and bone marrow cultures in 92% of cases during the acute febrile phase of illness. A biphasic culture method (Castaneda bottle) may improve the isolation rate form blood. Since it may take longer to grow Brucella species, the laboratory must be notified to extend the standard incubation time of 5 - 7 days. If a community laboratory (Level A) observes tiny, faintly staining gram negative coccobacilli with slow growing oxidase positive colonies on sheep blood, all plates and bottles should be placed in a biological safety cabinet. They should be appropriately packaged and shipped to a Level B or C laboratory. Confirmation in laboratories cases can be done by biochemical, slide agglutination or phage lysis tests.
The diagnosis of brucellosis is frequently made by serological tests. Acute and convalescent phase serum should be collected 3 - 4 weeks apart. A serum agglutination test (SAT) is available to detect both IgM and IgG antibodies. A titer of 1:160 or greater in a single specimen is considered indicative of active disease. ELISA and PCR methods are becoming more widely available.
The United States military recommends doxycycline (100 mg Q12 hr) plus rifampin (900 mg a day) for six weeks. Doxycycline for 6 weeks plus streptomycin for 2 - 3 weeks is an acceptable alternative. TMP/SMX for 4 - 6 weeks is less effective Long term therapy with a combination of a tetracycline, rifampin and an aminoglycoside is recommended for patients with meningoencephalitis or endocarditis. Valve replacement and surgical intervention for other forms of localized disease may be needed. Chemoprophylaxis is not generally recommended. For a high risk exposure to veterinary vaccine, inadvertent exposure in a laboratory or exposure in biological warfare context, a 3 - 6 weeks course of therapy with the agents used for treatment should be considered for prophylaxis.
Live animal vaccines are used widely and have eliminated brucellosis from most domestic animal herds in the US. No licensed human vaccine is available in the United States. A variant of Brucella abortus, S19-BA has been used in the former USSR. Efficacy is limited and annual revaccination is needed. A similar vaccine is available in China. Since brucellosis is not generally transmissible from person-to-person, standard precautions are adequate in managing patients. BSL-3 practices should be used for handling suspected Brucella cultures in the laboratory because of the danger of inhalation.
Glanders and Melioidosis
Caused by Burkholderia mallei and Burkholderia pseudomallei respectively (44). Both are gram negative bacilli with a "safety pin" appearance on microscopic exam. Burkholderia mallei, the causative agent of glander produces disease primarily in horses, mules and donkeys. Human disease is uncommon despite frequent and/or close contact with infected animals. Low concentrations of the organisms and less virulence for humans may be the factors responsible. The acute forms of the disease occur in mules and donkeys resulting in death in 3 to 4 weeks. The chronic form of the disease is more common in horses with lymphadenopathy, multiple skin nodules that ulcerate and drain, along with induration, enlargement and nodularily of regional lymphatics. The later presentation is called tarey. Human cases occur primarily in veterinarians and animal handlers. Infection is acquired from inhalation or contaminated injuries. B. pseudomallei, the causative agent of melioidosis is widely distributed in many tropical and subtropical regions. It is endemic in Southeast Asia and Northern Australia. Humans get infected by inhalation or contact with mucous membranes and skin. Melioidosis is one of the most common causes of community acquired septicemia in Northeastern Thailand. This represents a hazard to military personnel in those areas. In humans, the disease ranges from a subclinical infection to overwhelming septicemia with 90% mortality rate with 24 - 48 hours. Chronic and life threatening illness can also occur from reactivation of primary illness.
Aerosols from cultures of B. mallei and B. pseudomallei are highly infectious to laboratory workers making aerosol spread an efficient way of dissemination. A case of glanders in a military research microbiolgist was reported recently (45). Both of these organisms ave been viewed as potential biological warfare agents.
During World War I glanders was spread deliberately by central powers to infect large numbers of Russian horses and mules. This led to increase in human cases in Russia after World War I. The Japanese infected horses, civilians and prisoners of war with B. mallei at Pin Fang (China) Institute during World War II. The United States studied both agents as possible biological weapons in 1943-1944 but did not weaponize it. The former Soviet Union is believed to have experimented with B. mallei and B. pseudomallei as bioweapons.
The incubation period is 10 - 14 days. In the acute forms, both glanders and melioidosis can present as an acute pulmonary infection or as an acute fulminant, rapidly fatal septicemic illness. These are the forms that would be expected in case of their use as bioweapons. Acute infection of the oral, nasal and conjunctival mucosa can cause bloody nasal discharge with septal and turbinate nodules and ulcerations. Systemic invasion can cause a papular or pustular rash that can be mistaken for small pox as well as hepatic, splenic and pulmonary abscesses. Acute forms of the diseases carry a high mortality rate.
The chronic form is characterized by cutaneous and intramuscular abscesses on the legs and arms. Osteomyelitis, meningitis, and brain abscesses have also been reported.
Gram stain of the exudates show gram negative bacteria with bipolar staining. They stain irregularly with methylene blue or Wright's stain. The organisms can be cultured and identified with standard bacteriological methods.
For B. mallei, agglutination and complement fixation tests are available for serological diagnosis. Complement fixation tests are more specific and considered positive if the titer exceeds 1:20. For B. pseudomallei, a single titer above 1:160 with a compatible illness suggests active infection.
For localized disease, oral therapy with Amoxicillin /Clavulanate, tetracycline or TMP/SMX for 60 - 150 days is recommended. For severe disease, parenteral therapy with ceftazidime plus TMP/SMX for two weeks followed by oral therapy for six months is recommended. Post exposure chemoprophylaxis may be tried with TMP/SMX. No vaccine is available for human use. Standard precautions should be used for infection control purposes.
Category B - Viral Agents of Bioterrorism
Equine Encephalitis
Mosquito-borne alpha viruses cause Venezuelan equine encephalitis (VEE), Western equine encephalitis virus (WEE), and Eastern Equine Encephalitis (EEE) (44,49). They are similar, share many aspects of epidemiology and transmission and are often difficult to distinguish clinically. Natural infections are acquired by bites of a wide variety of mosquitoes. In natural epidemics severe and often fatal encephalitis in horses, mules, and donkeys precedes human cases. In a biological warfare attack with the virus disseminated as an aerosol, human disease would be a primary event or occur simultaneously with that in equidae. The human infective dose of VEE is 10 - 100 organisms. VEE is a febrile, relatively mild incapacitating illness. Encephalitis develops in a small percentage of patients. EEE and WEE viruses cause encephalitis predominately.
No specific therapy is available. Alpha-interferon and the interferon induce poly-ICLC have proven highly effective as post-exposure prophylaxis in experimental animals. A live attenuated vaccine is available as an investigational new drug. A formalin inactivated vaccine is available for boosting antibody titers in those initially receiving the live attentuated vaccine.
The viruses can be destroyed by heat (80OC for 30 minutes) and standard disinfection. There is no evidence for human-to-human or horse to human transmission. Standard precautions and vector control are adequate infection control procedures while the patient is febrile.
Category B - Biological Toxins
Ricin is a protein cytotoxin derived from the beans of the castor plant (Ricinus communis). The castor plant is ubiquitous and the toxin is easy to export. It is stable and highly toxic by several routes of exposure including inhalation (44,48).
Following inhalational exposure, acute onset of fever, chest tightness, cough, dyspnea, nausea and arthralgia occur within 4 - 8 hours. Acute respiratory distress syndrome in 18 - 24 hours is followed by hypoxemia and death in 36 - 72 hours. Ricin antigen can be detected in the serum and respiratory secretions by ELISA. Retrospective diagnosis is provided by antibody testing in acute and convalescent sera.
No specific therapy is available. Gastric lavage and emetics are indicated for ingestion. Being a large molecule, charcoal is not useful for ricin poisoning.
There is no vaccine or prophylactic immunotherapy available for human use. Immunization appears promising in animal models. A protective mask is the best protection against inhalation. Secondary aerosols are not a danger to others and ricin in non volatile. Standard precautions are adequate for health care workers. Hypochloric solution (0.1% sodium hypochloride) inactivates ricin.
Epsilon (Alpha) Toxin
Clostridium perfringens produces 12 toxins (49). One or more of them could be weaponized. The alpha toxin, a highly toxic phospholipase can be lethal when delivered as an aerosol. The toxin would cause vascular leaks and severe respiratory distress. It can also cause thrombocytopenia and liver damage. The toxin can be detected from serum and tissue samples by a specific immunoassay. Bacteria can be cultured easily. There is some data to show that clindamycin or rifampin may decrease the toxin production by C. perfringens. However, there is no specific prophylaxis against most of the C perfringens toxins. Some toxids are available for enteritis necroticans in humans. Veterinary toxids are widely used.
These toxins are proteins with a molecular weight of 23,000 - 29,000 daltons (44,49). Staphylococcus aureus produces a number of exotoxins and since they normally exert their effect on the GI tract thy are called Enterotoxins. They are also called Pyrogenic toxins because they cause fever. Staphylococcus Enterotoxin B (SEB) is a pyrogenic toxin that commonly causes food poisoning from improperly handled or refrigerated food. The effect of the inhaled SEB is markedly different. Symptoms occur at a very low inhaled dose (< 1/100th of the dose to cause GI symptoms). The diseases begins rapidly within 1 - 12 hours after ingestion with sudden onset of fever, chills, headache, myalgia and a nonproductive cough. Pulmonary edema occurs in severe cases. GI symptoms can occur concomitantly due to inadvertent swallowing of the toxin after inhalatione US Bioweapons program possessed prior to its termination in 1969.
There is no specific therapy available. Experimental immunization has been reported. No human vaccine is available. A candidate vaccine is in advanced development. Secondary aerosols are not a hazard and SEB does not pass through intact skin. Standard precautions for health care workers are recommended.
T-2 Mycotoxins
Trichothecene mycotoxins are a group of more than 40 toxins produced by common molds like Fusarium, Myrotecium, Trichoderma, Stachybotrys and other filamentous fungi. They are extremely stable in the environment and the only class of biological toxins that cause skin damage. Usual hypochlorite solution does not inactivate these toxins. They retain bioactivity even after autoclaving. Skin exposure causes pain, pruritus, reduess, vesicles, necrosis and sloughing. Severe irritant effects are seen on the respiratory tract, GI tract and eyes on contact. Severe intoxication results in shock and death. Diagnosis should be suspected if an aerosol attack occurs in the form of "yellow rain" with contamination of the clothes and the environment by pigmented oily fluids.
Treatment is supportive only. Soap and water washing can prevent or significantly reduce dermal toxicity if done within 1 - 6 hours. Superactivated charcoal should be used for oral intoxication.
No prophylactic chemotherapy or immunotherapy is available in the field . Exposure during an attack should be prevented by mask and clothing. Secondary aerosols are not a hazard. Contact with contaminated skin and contaminated clothing can produce secondary dermal exposures. Until decontamination is accomplished, contact precautions are needed. Subsequently, standard precautions are recommended for health care workers. Environmental decontamination requires 1% sodium hypochloride with 0.1% NAOH for 1 hour contact time.
Other Toxins With Potential for Bioterrorism
Tetanus toxin from C. tetani
Saxitoxin - a dinoflagellate toxin responsible for paralytic shellfish poisoning
Tetrodotoxin - A potent neurotoxin produced by fish, salamanders, frogs, octopus, starfish and mollusks
Toxins from blue-green algae
Class C Agents for Bioterroism
The agents in this group with the third highest priority include emerging pathogens that could be engineered for mass dissemination. The characteristics that render them amenable to bioterrorism are -
Ease of production and dissemination
Potential for high morbidity and mortality and major health impact
The agents included in this category are:
Nipah virus
Hantavirus - discussed in the presentation on viral hemorrhagic fevers
Tick borne hemorrhagic fever viruses
Tick borne encephalitis viruses
Yellow fever - discussed in the presentation on viral hemorrhagic fevers
Multidrug resistant tuberculosis
The 1998 - 1999 outbreak in Malaysia caused 1 million deaths in swine and encephalitis in 265 humans. The disease was eradicated from swine but is still likely to be present in fruit bats. Humans contracted Nipah virus by coming into direct contact with swine. Human-to-human transmission has not been documented. Mortality rate is about 40%. No cases have been documented in the United States.
Tick borne complex of viruses that cause encephalitis in humans include Far Eastern, Central European, Kyasanur Forest, Louping ill, Powassan and probably Negishi (50). Tick borne hemorrhagic fevers include Crimean-Congo hemorrhagic fever, Omsk hemorrhage fever and Kyasanur Forest disease (51).
Preparedness for the Public Health and Medical Communities
The CDC was designated by the Department of Health and Human Services to prepare the United States Public Health system to respond to a bioterrorism event (53). To enhance the preparedness at local and state levels, the CDC funded co-operative agreements with states and several large cities (54). Five areas were emphasized for the first 3 years (1999-2001) of this program -
Preparedness, planning and readiness assessment
Surveillance and epidemiology capacity
Biological laboratory capacity
Chemical laboratory capacity
Health alert network and training
The United States Food and Drug Administrations is participating in an interagency group preparing for response in a civilian emergency (55) The USAMRIID maintains an aeromedical isolation team to minimize the risk of transmission from the troops to air crews, caregivers and civilians (56).
Traditional first responders like firefighters and law enforcement officers are the most likely to respond to an announced attack, whereas physicians and other health care providers would be most likely to uncover an unannounced attack. In either case, the medical community at large will be responsible for diagnosis and management of diseases caused by biological and chemical weapons. ACP/ASIM has published a useful pocket guide to bioterrorism identification (Appendix C). The Association for Professionals in Infection Control and Epidemiology (APIC) in cooperation with the CDC has prepared a Bioterrorism Readiness Plan to serve as a reference document and a template to facilitate preparation of bioterrorism readiness plans for individual institutions (57). National Association of Counties conducted a survey of county Public Health directors (58). A significant number of responding counties (300 counties in 36 states) reported less than optimal levels of preparedness for biological and chemical warfare and for policies and procedures to enforce a quarantine. Among the reasons cited for unpreparedness were insufficient funding, insufficient work force and insufficient communications networks. In most cities, large health care institutions have disaster plans and various types of task forces with "experts" in different areas in place. However, they need to be updated and modified to include new information on biological and chemical weapons.
In addition to being able to recognize and manage diseases associated with bioterrorism events, health care providers will need to stay abreast of new developments. Use of Automated Ambulatory Care Encounter Records for Detection of Acute Illness Clusters, including Potential Bioterrorism Events, has been discussed in detail in a recent publication (59). The same issue of Emerging Infectious Diseases (August, 2002) has a review on the activity of humoral immunity against several biological agents and discusses the use of passive antibody administration (Immediate Immunity) as a specific defense against biological weapons (60).
Various models and estimates of the economic impact of bioterrorism attacks have been published. Rapid implementation of a post-attack prophylaxis program is the single most important means of reducing the huge economic impact (61). The model proposed by Kaufamnn et al. provides economic justification for preparedness measures.
We would like to conclude this discussion with a quote
"Modern adventurers like to up the ante, but even the most extreme sports wouldn't produce the adrenaline of a race against pandemic influenza or a cloud of anthrax at the Super Bowl. In the field of Infectious Diseases, reality is stranger than anything a writer could dream up. The most menacing bioterroist is Mother Nature herself."
Secret Agents: The Menace of Emerging Infections, by Madeline Drexler, John Henry Press, 2002
In the end, we wish to express our gratitude to Sarah Starks and Nancy Mutzbauer at the Southern Illinois University School of Medicine. Their assistance in collecting the most recent literature and helping convert thoughts and rough drafts into a presentable review was invaluable.
SYNC embryos hatched significantly later than ASYNC embryos (χ 2 =�.7, d.f. =𠂡, Pπ.001), with the median hatch time of ASYNC and SYNC embryos being 1.7 and 2.1 days, respectively, a delay of 10 h ( Fig.𠁒 ).
Top panel: L. peronii embryos and tadpoles were exposed to a diurnally-fluctuating UVBR-irradiance regime (12 h per day, 0830 to 2030) that had a peak in UVBR levels at the photoperiod midpoint (4 h per day, 1230 to 1630). The dotted line is the mean absolute irradiance of UVBR (W m 𢄢 ) of 10 spectral irradiance measurements taken at the surface of the water and the light grey shading around this dotted line is the S.D. ( Table𠁑 ). Middle panel: All L. peronii individuals were exposed to temperatures that fluctuated between 25଑ଌ and 35଑ଌ on a daily timescale, and L. peronii individuals either experienced synchronous fluctuations in UVBR and temperature, such that they experienced peak UVBR levels at 35ଌ (SYNC fluctuation regime: solid line), or asynchronous fluctuations in UVBR and temperature, such that they experienced peak UVBR levels at 25ଌ (ASYNC fluctuation regime: dashed line). Bottom panel: SYNC embryos (solid line) hatched later than ASYNC embryos (dashed line) (PϠ.001) but there was no effect of fluctuation regime on the hatching success of embryos (P =𠂠.30). Time 0 represents 0600 when egg masses were collected and the dark grey shading shows the time when the lights were off. Note that SYNC embryos experienced two full cycles of temperature fluctuations prior to hatching, whereas ASYNC embryos only experience one.
SYNC tadpoles had a burst swimming speed of 158ଔ mm s 𢄡 (mean ± S.E.), which was significantly slower than the burst swimming speed of ASYNC tadpoles, which was 175ଔ mm s 𢄡 (F1,81 =�, P =𠂠.002 in the analysis with tadpole total length not included as a covariate) ( Fig.� ). Burst swimming speed was positively associated with tadpole total length (F1,80 =�.2, Pπ.001 in the analysis with tadpole total length as a covariate), however, and when the effect of tadpole total length was accounted for, there was no effect of fluctuation regime on tadpole burst swimming performance (F1,80 =𠂢.1, P =𠂠.15 in the analysis with tadpole total length included as a covariate) ( Fig.� ), indicating that the effect of fluctuation regime on burst swimming performance was attributable to differences in tadpole total length.
SYNC and ASYNC denote the synchronous and asynchronous fluctuation regimes, respectively. (A) SYNC tadpoles had a burst swimming speed (Umax, mm s 𢄡 ) that was significantly slower than ASYNC tadpoles (P =𠂠.002), but when the effect of tadpole total length was accounted for, there was no effect of fluctuation regime on tadpole burst swimming performance (P =𠂠.15), indicating that the effect of fluctuation regime on burst swimming performance was attributable to differences in tadpole total length. (B) SYNC tadpoles were significantly smaller (PC 1) than ASYNC tadpoles (Pπ.001), and (C) there was no significant effect of fluctuation regime on tadpole survival time (min) in predation trials (P =𠂠.31). Data represent means ± SE and numbers in parentheses are the sample size.
SYNC tadpoles were significantly smaller than ASYNC tadpoles (PC 1: F1,99 =�.1, Pπ.001) ( Fig.� ) with the total length, body length, body width, and tail muscle width ( Fig.𠁔 ) of SYNC tadpoles being 10.9ଐ.1 mm, 3.9ଐ.04 mm, 2.6ଐ.03 mm and 0.58ଐ.04 mm, respectively, and the total length, body length, body width, and tail muscle width of ASYNC tadpoles being 11.5ଐ.1 mm, 4.1ଐ.05 mm, 2.7ଐ.03 mm and 0.63ଐ.01 mm, respectively.
The four measurements taken from the dorsal view were total length (TL), body length (BL), body width (BW), and tail muscle width (TMW).
There was no significant effect of fluctuation regime on tadpole survival time in predation trials (F1,87 =𠂡.05, P =𠂠.31) with the SYNC and ASYNC tadpoles surviving for 19ଔ min and 13଒ min, respectively ( Fig.� ).
Your Ultimate Guide to Appendicitis
Appendicitis occurs due to a blockage or obstruction in the appendix. The blockage may be due to a buildup of mucus, parasites, or most commonly, fecal matter. When an obstruction in the appendix occurs, bacteria can multiply quickly inside the organ causing the appendix to become irritated and swollen, thus leading to appendicitis.
The appendix is located in the lower right side of your abdomen and is a narrow, tube-shaped pouch protruding from your large intestine. If you don't get treatment for an inflamed appendix quickly it can rupture and release dangerous bacteria into your abdomen.
This will result in an infection called peritonitis. It is a serious condition that requires immediate medical attention. A ruptured appendix is a life-threatening situation which rarely occurs within the first 24 hours of symptoms. However, the risk of rupture rises dramatically after 48 hours of the onset of symptoms. It is therefore essential that you recognize symptoms immediately:
Symptoms of appendicitis
Appendicitis causes a variety of symptoms, including:
1. Dull abdominal pain near the navel or the upper abdomen which becomes sharp as it moves to the lower right abdomen. This is usually the first sign.
2. Loss of appetite.
3. Nausea and or vomiting soon after abdominal pain begins.
4. Abdominal swelling.
5. Fever of 99-102 degrees Fahrenheit.
6. Inability to pass gas.
Almost half the time, other symptoms of appendicitis appear, which include:
1. A dull or sharp pain anywhere in the upper or lower abdomen, back or rectum.
2. Painful urination.
3. Vomiting that preceded the abdominal pain.
4. Severe cramps.
5. Constipation or diarrhea with gas.
If you experience any of these symptoms, it is essential that you see a doctor immediately. A timely diagnosis and treatment are imperative. Do not eat, drink or use any pain medications, antacids, laxatives, or heating pads which can cause an inflamed appendix to rupture. It is vital that you take note of the below information:
1. Abdominal pain
Appendicitis involves a gradual onset of dull, cramping or aching pain throughout the abdomen. As the appendix becomes more swollen and inflamed, it will irritate the lining of the abdominal wall. This will cause a localized, sharp pain in the right lower part of the abdomen. The pain can be described as constant and severe, as opposed to the dull, aching pain that occurs when symptoms start. Some people may have an appendix that lies behind the colon. In such people, this can cause lower back pain or pelvic pain.
2. Mild fever
Appendicitis tends to cause a fever between 99&degF (37.2&degC) and 100.5&degF (38&degC). You may also experience chills. If the appendix bursts, this will result in an infection causing your fever to rise. A fever greater than 101&degF (38.3°) and an increase in heart rate may mean that the appendix has ruptured.
3. Digestive upset
Appendicitis can cause nausea and vomiting. You may lose your appetite and may also become constipated or have severe diarrhea. If you have trouble passing gas it may indicate a sign of a partial or total obstruction of your bowel. This may be related to underlying appendicitis.
What are the symptoms in children?
Children aged two and younger will often show the following symptoms:
1. Vomiting.
2. Abdominal bloating or swelling.
3. A tender Abdomen.
Older children and teenagers are likely to experience:
3. Pain in the lower right side of the abdomen.
What are the symptoms in pregnant women?
Most appendicitis symptoms are similar to the discomforts of pregnancy which include stomach cramping, nausea, and vomiting. But, it is not always clear that you have the classic symptoms of appendicitis, especially in late pregnancy. The growing uterus pushes the appendix higher during pregnancy, which means that pain may occur in the upper abdomen instead of the lower right side of the abdomen. You may also experience heartburn, gas or alternating episodes of constipation and diarrhea. The Do's and Don'ts
Do: Go to the hospital immediately if you or anyone you know has the aforementioned symptoms of appendicitis. Bear in mind that no home remedies will help.
Don't: Avoid over-the-counter medication to treat the symptoms and bear in mind that enemas and laxatives can cause your appendix to rupture. Furthermore, pain medications that mask symptoms may also make it harder for your doctor to make a quick diagnosis.
How is it treated?
A physical exam will be performed by your doctor asking you about your symptoms. Then, certain tests will be administered to help determine if you have appendicitis. These include blood tests to look for signs of an infection, urine tests to check for signs of a UTI or a kidney stone, an abdominal ultrasound or CT scan to see if the appendix is inflamed. Depending on your symptoms, your doctor may suggest immediate surgery in which case you will receive antibiotics before surgery.
After the surgery, you may stay in the hospital until the pain is under control and you are able to consume liquids. If you develop an abscess or if a complication occurs, your doctor may prescribe antibiotics for another day or two. Always remember that while its possible for problems to arise, most people make a full recovery without complications.
Risk factors and prevention
Appendicitis can happen at any time, though it is most likely to occur between the ages of 10 and 30. It is more common in men than in women. You can't prevent appendicitis, but you can lower the risk of developing it. It seems less likely if you have a diet rich in fiber, so opt for fresh fruits and vegetables whenever you can. Increasing your fiber intake can prevent constipation and subsequent stool buildup which is the most common cause of appendicitis. If you suffer from any condition that causes inflammation or infection of the bowels, it is vital that you work with your doctor to prevent appendicitis.
Did coronavirus originate in Chinese government laboratory?
The Wuhan Institute of Virology has been collecting numerous coronaviruses from bats ever since the SARS outbreak in 2002.
They have also published papers describing how these bat viruses have interacted with human cells.
US Embassy staff visited the lab in 2018 and 'had grave safety concerns' over the protocols which were being observed at the facility.
The lab is just eight miles from the Huanan wet market which is where the first cluster of infections erupted in Wuhan.
The market is just a few hundred yards from another lab called the Wuhan Centers for Disease Prevention and Control (WHCDC).
The WHCDC kept disease-ridden animals in its labs, including some 605 bats.
Those who support the theory argue that Covid-19 could have leaked from either or both of these facilities and spread to the wet market.
Most argue that this would have been a virus they were studying rather than one which was engineered.
Last year a bombshell paper from the Beijing-sponsored South China University of Technology recounted how bats once attacked a researcher at the WHCDC and 'blood of bat was on his skin.'
The report says: 'Genome sequences from patients were 96% or 89% identical to the Bat CoV ZC45 coronavirus originally found in Rhinolophus affinis (intermediate horseshoe bat).'
It describes how the only native bats are found around 600 miles away from the Wuhan seafood market and that the probability of bats flying from Yunnan and Zhejiang provinces was minimal.
In addition there is little to suggest the local populace eat the bats as evidenced by testimonies of 31 residents and 28 visitors.
Instead the authors point to research being carried out within 300 yards at the WHCDC.
One of the researchers at the WHCDC described quarantining himself for two weeks after a bat's blood got on his skin, according to the report. That same man also quarantined himself after a bat urinated on him.
And he also mentions discovering a live tick from a bat - parasites known for their ability to pass infections through a host animal's blood.
'The WHCDC was also adjacent to the Union Hospital (Figure 1, bottom) where the first group of doctors were infected during this epidemic.' The report says.
'It is plausible that the virus leaked around and some of them contaminated the initial patients in this epidemic, though solid proofs are needed in future study.'
The authors of the document insist that a third world war 'will be biological', unlike the first two wars which were described as chemical and nuclear respectively.
Referencing research which suggested the two atomic bombs dropped on Japan forced them to surrender, and bringing about the end of WWII, they claim bioweapons will be 'the core weapon for victory' in a third world war.
The document also outlines the ideal conditions to release a bioweapon and cause maximum damage.
The scientists say such attacks should not be carried out in the middle of a clear day, as intense sunlight can damage the pathogens, while rain or snow can affect the aerosol particles.
Instead, it should be released at night, or at dawn, dusk, or under cloudy weather, with 'a stable wind direction. so that the aerosol can float into the target area'.
Meanwhile, the research also notes that such an attack would result in a surge of patients requiring hospital treatment, which then 'could cause the enemy's medical system to collapse'.
Other concerns include China's 'Gain of Function' research at the Wuhan Institute of Virology - near where the first Covid outbreak was discovered - at which virologists are creating new viruses said to be more transmissible and more lethal.
MP Tom Tugendhat, chairman of the foreign affairs committee, said: 'This document raises major concerns about the ambitions of some of those who advise the top party leadership. Even under the tightest controls these weapons are dangerous.'
Chemical weapons expert Hamish de Bretton-Gordon said: 'China has thwarted all attempts to regulate and police its laboratories where such experimentation may have taken place.'
The revelation from the book What Really Happened in Wuhan was reported yesterday.
The document, New Species of Man-Made Viruses as Genetic Bioweapons, says: 'Following developments in other scientific fields, there have been major advances in the delivery of biological agents.
'For example, the new-found ability to freeze-dry micro-organisms has made it possible to store biological agents and aerosolise them during attacks.'
It has 18 authors who were working at 'high-risk' labs, analysts say.
Australian Strategic Policy Institute executive director Peter Jennings also raised concerns over China's biological research into coronaviruses potentially being weaponised in future.
'There is no clear distinction for research capability because whether it's used offensively or defensively is not a decision these scientists would take,' he said.
'If you are building skills ostensibly to protect your military from a biological attack, you're at the same time giving your military a capacity to use these weapons offensively. You can't separate the two.'
Intelligence agencies suspect Covid-19 may be the result of an inadvertent Wuhan lab leak. But as yet there is no evidence to suggest it was intentionally released.
Only this week, Brazil President Jair Bolsonaro appeared to strongly criticise China by accusing it of creating Covid to spark a chemical 'warfare.'
The comments were made during a press conference on Wednesday as the hardline leader sought to further distance himself from the growing attacks over his domestic handling of a pandemic that has produced the second-highest death toll in the world.
'It's a new virus. Nobody knows whether it was born in a laboratory or because a human ate some animal they shouldn't have,' Bolsonaro said.
'But it is there. The military knows what chemical, bacteriological and radiological warfare. Are we not facing a new war? Which country has grown its GDP the most? I will not tell you.'
While Bolsonaro did not name China in his speech, data from the Organization for Economic Cooperation and Development showed that China was the only G20 member whose GDP showed a growth during the pandemic in 2020, expanding by 2.3%.
The dossier by People's Liberation Army scientists and health officials examined the manipulation of diseases to make weapons 'in a way never seen before'
Brazil's hardline President appears to claim China created Covid to spark a 'chemical war'
And the World Health Organization chief said as recently as March that all theories on the origins of Covid-19 remained open after reading the WHO-China study – despite the claim the report dismissed the notion that the virus escaped from a lab as 'extremely unlikely'.
Tedros Adhanom Ghebreyesus said all of the hypotheses are 'on the table' and require further investigation after reading the report from the international experts' mission to Wuhan.
But his comments came just hours after it emerged the report dismissed the lab leak theory and said the transmission of the virus from bats to humans through another animal is the most likely scenario.
The report's release was repeatedly delayed, raising questions about whether the Chinese side was trying to skew the conclusions to prevent blame for the pandemic falling on China.
Critics including ex-President Trump have accused the WHO of parroting Chinese propaganda on the virus since the outbreak was first announced to the world.
The comments by Dr Tedros came after New York Republican Representative Lee Zeldin slammed China for 'covering up to the world the pandemic's origins', while the WHO 'has played along time and time again'.
Meanwhile, Dr Anthony Fauci, President Biden's chief medical adviser, revealed he has 'concerns' over the WHO's controversial fact-finding mission.
Repeated delays in the report's release raised questions about whether the Chinese side was trying to skew its conclusions.
'We've got real concerns about the methodology and the process that went into that report, including the fact that the government in Beijing apparently helped to write it,' U.S. Secretary of State Antony Blinken said in a recent CNN interview.
China rejected that criticism and accused the US of 'exerting political pressure' on the fact-finding mission experts.
'The US has been speaking out on the report. By doing this, isn't the U.S. trying to exert political pressure on the members of the WHO expert group?' asked Foreign Ministry spokesperson Zhao Lijian.
Worrying new clues about the origins of Covid: How scientists at Wuhan lab helped Chinese army in secret project to find animal viruses, writes IAN BIRRELL
Scientists studying bat diseases at China's maximum-security laboratory in Wuhan were engaged in a massive project to investigate animal viruses alongside leading military officials – despite their denials of any such links.
Documents obtained by The Mail on Sunday reveal that a nationwide scheme, directed by a leading state body, was launched nine years ago to discover new viruses and detect the 'dark matter' of biology involved in spreading diseases.
One leading Chinese scientist, who published the first genetic sequence of the Covid-19 virus in January last year, found 143 new diseases in the first three years of the project alone.
The fact that such a virus-detection project is led by both civilian and military scientists appears to confirm incendiary claims from the United States alleging collaboration between the Wuhan Institute of Virology (WIV) and the country's 2.1 million-strong armed forces.
The scheme's five team leaders include Shi Zhengli, the WIV virologist nicknamed 'Bat Woman' for her trips to find samples in caves, and Cao Wuchun, a senior army officer and government adviser on bioterrorism.
Prof Shi denied the US allegations last month, saying: 'I don't know of any military work at the WIV. That info is incorrect.'
QUESTIONS: Colonel Cao Wuchun, a WIV adviser, and, right, Major General Chen Wei, China's top biodefence expert
Yet Colonel Cao is listed on project reports as a researcher from the Academy of Military Medical Sciences of the People's Liberation Army, works closely with other military scientists and is director of the Military Biosafety Expert Committee.
Cao, an epidemiologist who studied at Cambridge University, even sits on the Wuhan Institute of Virology's advisory board. He was second-in-command of the military team sent into the city under Major General Chen Wei, the country's top biodefence expert, to respond to the new virus and develop a vaccine.
The US State Department also raised concerns over risky 'gain of function' experiments to manipulate coronaviruses at the Wuhan lab and suggested researchers fell sick with Covid-like symptoms weeks before the outbreak emerged more widely in the Chinese city.
Last month, Britain, the US and 12 other countries criticised Beijing for refusing to share key data and samples after a joint World Health Organisation and Chinese study into the pandemic's origins dismissed a lab leak as 'extremely unlikely'.
Filippa Lentzos, a biosecurity expert at King's College London, said the latest disclosures fitted 'the pattern of inconsistencies' coming from Beijing.
'They are still not being transparent with us,' she said. 'We have no hard data on the pandemic origins, whether it was a natural spill-over from animals or some kind of accidental research-related leak, yet we're unable to get straight answers and that simply does not inspire confidence.'
Case Definitions for Chemical Poisoning
The material in this report originated in the National Center for Environmental Health, Henry Falk, MD, Director and the Division of Environmental Hazards and Health Effects, Michael McGeehin, PhD, Director.
Corresponding preparer: Martin Belson, MD, Medical Toxicologist, Acting Team Leader, Environmental Toxins and Chemicals Team, Health Studies Branch, CDC/NCEH/DEHHE, 4770 Buford Highway, MS F-46, Atlanta, GA 30341 Telephone: 770-488-3425 Fax: 770-488-3450 E-mail: [email protected]
When human illness results from an unintentional or intentional release of a toxin (chemicals produced by metabolism in an organism [e.g., ricin]) or a toxicant (natural or synthetic chemicals not metabolically produced by an organism [e.g., nerve agents]) into the environment, uniform reporting is necessary to direct appropriate resources, assess the extent of morbidity and mortality, track poisoned persons, and monitor response to intervention. In this report, CDC presents case definitions to facilitate uniform reporting among local, state, and federal public health agencies of illness resulting from a chemical release. The report also explains the rationale for the structure of the case definitions, the audience for whom it is intended, the setting in which the case definitions might be used, and reasons each chemical presented in the report was selected.
Clinical knowledge and diagnostic tools (e.g., biologic laboratory tests) for detecting chemical poisoning are likely to improve over time. CDC will create new case definitions and revise existing definitions to meet the needs related to emerging threats and to enhance case definition sensitivity and specificity, when possible, with developing clinical information.
Toxins are chemicals that are produced by organisms as a result of cellular metabolism (e.g., marine toxins such as saxitoxin or plant toxins such as ricin). Toxicants are synthetic (i.e., manufactured) or naturally found chemicals that are not produced by organisms as a result of cellular metabolism (e.g., nerve agents or arsenic). When illness results from an intentional or unintentional chemical release (either known or suspected on the basis of a credible threat) into the environment, uniform reporting is paramount to direct appropriate resources, assess the extent of morbidity and mortality, track poisoned persons, and monitor response to intervention. In this report, CDC presents case definitions to facilitate uniform reporting of illness resulting from a chemical (i.e., toxin and toxicant) release.
How This Report Is Organized
The report provides an overview of 1) the settings in which the case definitions might be used, 2) the structure of the case definitions, 3) the rationale for choosing the particular chemicals, and 4) plans for revising the report. A list and description of the terms used in the report are also provided. In addition, case definitions, which include reference citations, are presented for the selected chemicals.
How To Use the Information in This Report
The case definitions in this report should be used by clinicians and public health officials in two settings: 1) after a credible threat of a chemical release or 2) after a known chemical release. The list of chemicals that have the potential for use as a terrorist weapon is extensive, and clinical presentation of poisoning from chemicals can be similar to that of common diseases (e.g., gastroenteritis). Therefore, use of these case definitions as a surveillance tool, in the absence of a credible threat or a known chemical release, typically results in excessive false-positive reports and is not recommended by CDC.
Case definitions are not sufficient for establishing a medical diagnosis and should not be relied upon to initiate therapy. They are also not meant to be used for persons who are exposed to a chemical agent but remain asymptomatic. Clinical manifestations of poisonings might vary as a result of interindividual differences (e.g., previous medical history, genetic differences, sex, or age), route of exposure, amount and duration of exposure, and length of time since the exposure. In addition, simultaneous exposure to > 2 chemicals can result in symptoms that are not typical for either agent alone. Use of additional clinical, epidemiologic, and laboratory data might enable a physician to make a medical diagnosis, although the formal surveillance case definition might not be met.
Health-care providers should report suspect cases of intentional chemical exposure to their local poison-control center and to a public health agency. Local and state public health officials should notify CDC and law enforcement officials if they identify persons who might have been exposed to intentional chemical poisoning.
Structure of the Case Definition
CDC modeled the structure of the chemical poisoning case definitions in this report after the infectious disease case definitions that were previously developed by CDC and the Council of State and Territorial Epidemiologists (CSTE) ( 1,2 ). However, case definitions for chemical poisoning were modified to address the clinical and diagnostic challenges unique to chemical poisoning. A description of terminology used in the case definitions is presented in this report.
Each case definition is composed of three sections: 1) clinical description, 2) laboratory criteria for diagnosis, and 3) case classification. Individual case definitions differ in the structure of the clinical description and the laboratory criteria for diagnosis. However, for all case definitions, the clinical description and the laboratory criteria for diagnosis will determine the case classification. CDC used an algorithmic method to determine the structure of the clinical description and the laboratory criteria and to determine how the user might classify a case by using the case definition (Figure).
For case classifications, a case that is being considered as a chemical poisoning case is categorized as &quotsuspected," &quotprobable," or &quotconfirmed." A suspected case is one in which any potentially exposed person is being evaluated by health-care workers or public health officials for poisoning by a particular chemical agent however, no specific credible threat exists. A probable case is 1) one in which a person has an illness that is clinically compatible with poisoning from a particular chemical agent and in which a credible threat exists (e.g., clinically compatible illness in an employee of a facility where a specific threat of a chemical release is made) or 2) one in which epidemiologic data link the person to a confirmed case (e.g., clinically compatible illness in a person who was at the same location as the subject of a case confirmed by biologic or environmental testing). A confirmed case is one in which a suspected or a probable case of exposure has been substantiated with laboratory testing of environmental or biologic specimens.
One of the key elements in determining whether a potentially exposed person will be categorized as a suspected case-patient or a probable case-patient is deciding whether the person's illness is clinically compatible with exposure to a particular chemical. Providing the user of these case definitions with a specific set of clinical criteria (i.e., clinical criteria that objectively allow the user to decide whether the case is clinically compatible) is often not possible, because manifestations of chemical poisonings can vary on the basis of individual differences of the exposed persons (e.g., previous medical history, genetic differences, sex, or age), route of exposure, amount and duration of exposure, and length of time since the exposure. Therefore, the structure of the clinical description includes multiple possible clinical manifestations.
If a valid laboratory test is available to confirm the exposure for a particular agent (e.g., cyanide), the clinical description summarizes the most notable features of acute poisoning from that particular chemical, on the basis of the medical literature. If no available or valid laboratory method is available to detect the chemical in biologic or environmental specimens, the case will never be confirmed and will remain either in the suspected or probable category. Therefore, making an association between the clinical presentation and the suspected agent will primarily depend on the clinical description and the presence of a credible threat. For these agents (e.g., tetrodotoxin), the clinical description of the case definition includes specific criteria for clinical compatibility (including nonconfirmatory or nonspecific laboratory parameters [e.g., electrolytes and renal function tests]) that should be met before a case can be categorized as suspected or probable for chemical poisoning. Medical toxicologists and epidemiologists at CDC used clinical information from the literature on each agent to develop the specific criteria included in the clinical description for that agent. However, CDC recognizes that the criteria do not provide positive or negative predictive value for confirming or excluding poisoning from a particular chemical.
In certain instances, suspected or probable cases might exist for which laboratory (biologic or environmental) testing was not performed by the clinician or public health official. Reasons for not performing laboratory testing might include a predominant amount of clinical and nonspecific laboratory evidence of a particular chemical or a 100% certainty of the etiology of the agent, as might be the case with agricultural workers who are known to have been exposed to a particular fumigant and who then develop clinically compatible illness. For example, in the case of a Bulgarian dissident reported to have been poisoned with ricin, no laboratory confirmation ever occurred ( 3 ). If the case definitions in this report are strictly followed, this case might never be a confirmed case, although a predominant amount of evidence existed for ricin poisoning, and ricin poisoning is accepted as the cause of death. This case and similar scenarios may be considered as confirmed.
A suspected or probable case can become a confirmed case when excess exposure is verified by laboratory evidence (i.e., levels above the 95th percentile in CDC population studies or above a reference range). Laboratory evidence can be obtained from either biologic specimens (e.g., blood or urine) or environmental samples (e.g., water, air, soil, or a contaminated product such as food). Testing for chemicals in either environmental or biologic specimens is not universally available. In addition, results from field tests conducted by using hand-held assays intended for screening environmental samples and research tests are not considered confirmatory. CDC recommends that laboratory testing be used in conjunction with a state or CDC public health investigation for confirming exposure only when a valid laboratory test is available through 1) commercial resources, 2) the Laboratory Response Network (LRN), or 3) one of the following federal agencies (Appendix):
Food and Drug Administration (FDA), Forensic Chemistry Center --- Processes food samples for selected agents. Available at http://www.fda.gov telephone: 513-679-2700, extension 184.
CDC, National Center for Environmental Health (NCEH), Division of Laboratory Sciences --- Processes blood and urine for selected agents. Available at http://www.cdc.gov/nceh/dls telephone: 770-488-7950.
CDC, National Institute for Occupational Safety and Health (NIOSH) --- Processes air, dust, and soil for selected agents from workplace exposures. Available at http://www.cdc.gov/niosh/homepage.html telephone: 800-356-4674.
CDC, National Center for Infectious Diseases (NCID), Bioterrorism Rapid Response and Advanced Technology Laboratory --- Receives and processes clinical and environmental samples for biothreat agents and selected biotoxins. Telephone: 404-639-4910.
Environmental Protection Agency (EPA) --- Processes environmental samples for industrial chemicals. Available at http://www.epa.gov telephone: 404-562-8700.
LRN includes multiple state laboratories capable of identifying select microbiologic agents, but only a limited number of state laboratories are capable of testing biologic specimens for chemical warfare agents.
Data for validation of commercially available analyses of certain chemicals in either biologic or environmental samples might be difficult for nonlaboratorians to access. If an intentional release occurs, CDC personnel will be able to advise local and state public health partners on whether valid analyses for biologic samples for specific chemicals exist. However, CDC does not provide guidance concerning commercial laboratory methods for guidance regarding environmental or food samples, consultation with EPA and FDA is recommended. Laboratorians should ask their referral laboratories to provide confirmation that a method is analytically valid for precision, detection limits, and accuracy. Laboratorians should also ask their laboratories to confirm whether applications are environmental or clinical, for example.
A chemical agent probably will be detected in biologic specimens in traceable quantities in the absence of clinical findings. However, signs and symptoms consistent with poisoning should develop before an exposed person is considered a case-patient.
Because timely laboratory confirmation might not be available, clinicians should not wait for laboratory verification to report suspected or probable cases to appropriate public health agencies. Early involvement of public health agencies will enable monitoring of trends, detection of covert events in multiple locations, mobilization of resources (e.g., National Pharmaceutical Stockpile, laboratory resources, or legal investigation), and containment of further exposure. State health departments should continue to promptly report suspected cases to CDC, and records should be updated with the appropriate classification status when additional surveillance information becomes available.
Chemicals with Potential for Terrorist Use and Plans for Revision of This Report
The substantial number of chemicals with potential for terrorist use precludes the development of a case definition for each possible agent. Therefore, certain agents with a potential for use as a terrorist weapon are not included in this report. Medical toxicologists at CDC's NCEH chose the chemicals presented in this report on the basis of knowledge of their accessibility, deliverability, lethality, potential to cause social disruption, or historic use. In certain cases, a category of agents with similar properties is represented (e.g., caustics/corrosives).
This report underwent an extensive review process by CDC's Office of Security and Emergency Preparedness and Office of Terrorism Preparedness and Emergency Response, and by CDC's stakeholders (e.g., FDA, EPA, and CSTE). This report is designed to be updated and revised as new information becomes available. CDC plans to compose, in conjuction with state public health agencies and other organizations (e.g., FDA or EPA), new case definitions and revise existing definitions to reflect information concerning emerging threats and agents, improvements in diagnostic technology, and increasing clinical knowledge regarding a particular chemical. In addition, when a chemical is released or the threat of a release exists, CDC will review literature regarding the implicated chemical and might update the case definition. The most up-to-date versions of case definitions and other public health documents will be posted on CDC's Emergency Preparedness and Response Internet site (http://www.bt.cdc.gov/agent/agentlistchem.asp).
Terms Used in This Report
Clinically compatible case. A case in which a person has signs and symptoms compatible with poisoning by a particular agent.
Epidemiologically linked case. A case that meets one of the following criteria:
A case in which direct exposure to the agent was detected in a confirmed case (e.g., persons eating the same food that was implicated in an illness in a laboratory-confirmed case).
A case in which contact with at least one person directly exposed to the agent and confirmed to be a case-patient (this might not apply to certain chemical agents such as gases) has made contact with
--- clothing of the confirmed case-patients or
--- biologic specimens (e.g., vomitus or blood) of at least one confirmed case.
Valid laboratory test. A biologic laboratory test that has been analytically, and in part, clinically validated. A test should be considered valid before it can be considered confirmatory. Analytical validation requires development of a definable and repeatable calibration-response relationship (e.g., linearity), demonstration studies of accuracy and imprecision, interference testing, and establishment of the limits of detection. Minimal clinical validation might include previous application to human situations and an understanding of background levels in noncases. Further clinical validation should include estimates of prevalence at known thresholds studies of applied sensitivity, specificity, and predictive value and demonstration of concentration-effect relationships.
For clinical laboratories, the individual laboratory, in conjunction with guidelines established by the Clinical Laboratory Improvement Act, is responsible for ensuring validation. For environmental laboratories, the typical requirements for competence of testing are set by the International Organization for Standardization (IOS Standard 17025).
Commercially available test. A test that is available to health investigators through either fee-for-service pathways or state public health and LRN laboratories that satisfy validation requirements. Typically, commercial regional laboratories can assist with only a limited number of the chemical measurements given in the case definitions (e.g., blood cyanide).
Laboratory confirmation. Laboratory evidence of exposure (i.e., levels above known background levels) either through a biologic specimen (e.g., blood or urine) or environmental samples (e.g., samples of water, air, soil, or a contaminated product such as food). A valid laboratory test should be available commercially, through federal agencies (i.e., CDC, FDA, or EPA), or through LRN.
Suspected case. A case in which a potentially exposed person is being evaluated by health-care workers or public health officials for poisoning by a particular chemical agent, but no specific credible threat exists.
Probable case. A clinically compatible case in which a high index of suspicion (i.e., a credible threat) exists for exposure to a particular agent, or a case with an epidemiologic link to a laboratory-confirmed case.
Confirmed case. A clinically compatible case with laboratory confirmation by using either biologic or environmental samples. The case can be confirmed if laboratory testing was not performed because either a predominant amount of clinical and nonspecific laboratory evidence of a particular chemical was present or a 100% certainty of the etiology of the agent is known.
Case Definitions for Potential Terrorism Agents: Toxins and Toxicants*
Adamsite (Diphenylaminechloroarsine or DM)
Clinical Description
The majority of exposures occur by inhalation and typically lead to symptoms of ocular, nasal, and respiratory tract irritation. Nonspecific gastrointestinal symptoms (e.g., vomiting or diarrhea) might also occur. The effects of adamsite poisoning take minutes to begin and might last for hours ( 4 ). If a rapid onset of manifestations of one of the following respiratory effects occurs, the clinical description for adamsite poisoning has been met: nose or throat irritation, cough, or dyspnea.
Laboratory Classification for Diagnosis
Biologic. No biologic marker is available for adamsite exposure.
Environmental. No method is available to detect adamsite in environmental samples.
Case Classification
Suspected. A case in which a potentially exposed person is being evaluated by health-care workers or public health officials for poisoning by a particular chemical agent, but no specific credible threat exists.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for adamsite exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Confirmed. A clinically compatible case in which laboratory tests (not available for adamsite) have confirmed exposure.
The case can be confirmed if laboratory testing was not performed because either a predominant amount of clinical and nonspecific laboratory evidence of a particular chemical was present or a 100% certainty of the etiology of the agent is known.
The majority of exposures occur by inhalation and typically lead to symptoms of ocular, nasal, and respiratory irritation. Signs and symptoms of poisoning might include eye redness and lacrimation, nose and throat irritation, cough, suffocation or choking sensation, and dyspnea ( 5--7 ).
Laboratory Criteria for Diagnosis
Biologic. No biologic marker is available for ammonia exposure.
Environmental. Detection of ammonia in environmental samples, as determined by NIOSH.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for ammonia exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Confirmed. A clinically compatible case in which laboratory tests of environmental samples have confirmed exposure.
Arsenic (Inorganic)
Acute ingestion of toxic amounts of inorganic arsenic typically causes severe gastrointestinal signs and symptoms (e.g., vomiting, abdominal pain, and diarrhea). These signs and symptoms might rapidly lead to dehydration and shock. Different clinical manifestations might follow, including dysrhythmias (prolonged QT, T-wave changes), altered mental status, and multisystem organ failure that might ultimately result in death ( 8--11 ).
Biologic. A case in which elevated urinary arsenic levels (&gt50 µ g/L for a spot or &gt50 µ g total for a 24-hour urine) exist, as determined by commercial laboratory tests. Speciation is required in all cases where total urine arsenic is elevated to differentiate the amount of organic and inorganic arsenic.
Environmental. Detection of arsenic in environmental samples above typical background levels, as determined by NIOSH or FDA.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for arsenic exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Confirmed. A clinically compatible case in which laboratory tests have confirmed exposure.
Arsine
Inhalation of arsine gas causes no immediate symptoms. Signs and symptoms occur 2--24 hours after exposure and result from massive hemolysis. These signs and symptoms include generalized weakness, dark urine, jaundice, and dyspnea. Oliguria and renal failure often occur 1--3 days after exposure ( 12--14 ).
Biologic. No specific test is available for arsine exposure however, exposure to arsine might be indicated by detection of elevated arsenic levels in urine (&gt50 µ g/L for a spot or &gt50 µ g for a 24-hour urine) and signs of hemolysis (e.g., hemoglobinuria, anemia, or low haptoglobin).
Environmental. Detection of arsine in environmental samples, as determined by NIOSH.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for arsine exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Ingestion of certain forms of barium (e.g., barium carbonate or barium fluoride) in toxic amounts leads to gastrointestinal symptoms (e.g., vomiting, abdominal pain, and watery diarrhea). Within 1--4 hours of ingestion, profound hypokalemia develops in certain instances, and potassium levels &lt1.0 mmol/L are associated with generalized muscle weakness that might progress to paralysis of the limbs and respiratory muscles ( 15--19 ).
Barium sulfate is not absorbed when taken by mouth and is therefore commonly used as a contrast agent for radiographic procedures.
Biologic. A case in which an elevated spot urine barium level (&gt7 µ g/L) exists ( 20 ), as determined by commercial laboratory tests.
Environmental. Elevation of barium compounds in environmental samples, as determined by NIOSH or FDA.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for barium exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Brevetoxin
After oral ingestion, brevetoxin poisoning is characterized by a combination of gastrointestinal and neurologic signs and symptoms. The incubation period ranges from 15 minutes to 18 hours. Gastrointestinal symptoms include abdominal pain, vomiting, and diarrhea. Neurologic symptoms include paresthesias, reversal of hot and cold temperature sensation, vertigo, and ataxia. Inhalational exposure to brevetoxin results in cough, dyspnea, and bronchospasm ( 21--24 ).
Biologic. Brevetoxin can be detected by an enzyme-linked immunosorbent assay (ELISA) method in biologic samples however, ELISA of biologic samples is not a certified method for detection of brevetoxin.
Environmental. Any concentration of brevetoxin in environmental samples ( 25 ), as detected by a commercial laboratory.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for brevetoxin exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Confirmed. A clinically compatible case in which laboratory tests on environmental samples are confirmatory.
The majority of exposures to bromine occur by inhalation and typically lead to symptoms of ocular, nasal, and respiratory irritation. Signs and symptoms of poisoning include eye redness and lacrimation, nose and throat irritation, cough, and dyspnea. Ingestion of liquid bromine can cause abdominal pain and hemorrhagic gastroenteritis with secondary shock. Signs and symptoms might also include brown discoloration of mucous membranes and the tongue ( 26,27 ).
Biologic. No specific test for bromine is available however, detection of elevated bromide levels in serum (reference level is 50--100 mg/L) might indicate that an exposure has occurred.
Environmental. Detection of bromine in environmental samples, as determined by NIOSH.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for bromine exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
3-Quinuclidinyl Benzilate (BZ)
BZ toxicity, which might occur by inhalation, ingestion, or skin absorption, is an anticholinergic syndrome consisting of a combination of signs and symptoms that might include hallucinations agitation mydriasis (dilated pupils) blurred vision dry, flushed skin urinary retention ileus tachycardia hypertension and elevated temperature (&gt101 º F). The onset of incapacitation is dose-dependent. It might occur as early as 1 hour after exposure and continue up to 48 hours ( 28 ).
Biologic. A case in which BZ is detected in urine ( 29 ), as determined by CDC.
Environmental. No method is available for detecting BZ in environmental samples.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for BZ exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Confirmed. A clinically compatible case in which laboratory tests on biologic samples have confirmed exposure.
The predominant manifestations of carbon monoxide poisoning are cardiovascular and neurologic effects. Inhalation of carbon monoxide gas typically leads to headache, dizziness, and confusion, which might progress to dyspnea, tachypnea, syncope, and metabolic acidosis ( 30--32 ).
Biologic. A case in which carboxyhemoglobin concentration exists &gt5% in venous or arterial blood in nonsmokers and &gt10% in smokers, as determined by hospital or commercial laboratory tests. The typical range of carboxyhemoglobin concentrations in smokers is 6%--10% ( 32 ).
Environmental. No confirmatory test is available for carbon monoxide in environmental samples.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for carbon monoxide exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Caustic or Corrosive Agents
Ingestion of caustic or corrosive agents (e.g., phosphoric acid or sulfuric acid) can cause direct injury to tissue upon exposure, which might lead to the following signs and symptoms: oral pain, ulcerations, drooling, dysphagia, vomiting, and abdominal pain. Dermal and ocular exposure might result in local irritation or burn injury. Inhalation of corrosive gases might result in upper and lower respiratory irritation, leading to stridor, dyspnea, wheezing, and pulmonary edema ( 33--36 ).
Biologic. No biologic marker for exposure to a caustic or corrosive agent is available.
Environmental. Detection of caustic or corrosive agents in environmental samples, as determined by NIOSH or FDA.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for a caustic exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
The majority of exposures occur by inhalation and typically lead to symptoms of ocular, nasal, and respiratory irritation. Signs and symptoms of poisoning might include eye redness and lacrimation, nose and throat irritation, cough, suffocation or choking sensation, and dyspnea. For cutaneous exposures, burning, blistering, and frostbite injury to the skin are possible ( 37,38 ).
Biologic. No biologic marker for chlorine exposure is available.
Environmental. Detection of chlorine in environmental samples, as determined by NIOSH.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for chlorine exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Ingestion of colchicine typically leads to profuse vomiting and diarrhea, which can be bloody, followed by hypovolemic shock and multisystem organ failure within 24--72 hours. Coma, convulsions, and sudden death might also occur. Subsequent complications include bone marrow suppression with resultant leukopenia, thrombocytopenia (nadir in 4--7 days), and possibly sepsis ( 39 ).
Biologic. A case in which colchicine is detected in urine, serum, or plasma ( 40 ), as determined by a commercial laboratory.
Environmental. Detection of colchicine in environmental samples, as determined by FDA.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for colchicine exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Inhalation of cyanide gas or ingestion of cyanide salts typically leads to lethargy or coma (possibly sudden collapse), dyspnea, tachypnea, tachycardia, and hypotension. Severe poisoning results in bradypnea, bradycardia, cardiovascular collapse, and death. Nonspecific laboratory findings include metabolic and lactic acidosis ( 41--43 ).
Biologic. A case in which cyanide concentration is higher than the normal reference range (0.02--0.05 µ g/mL) in whole blood ( 43 ), as determined by a commercial laboratory.
Environmental. Detection of cyanide in environmental samples, as determined by NIOSH or FDA.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for cyanide exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Signs and symptoms of acute digitalis (digoxin or digitoxin) poisoning by ingestion include primarily gastrointestinal effects (nausea and vomiting), hyperkalemia, and cardiovascular effects (bradydysrhythmias [heart rate &lt60 or atrioventricular block] or tachydysrhythmias [ventricular tachycardia/fibrillation or atrial tachycardia with 2:1 block]) ( 44--46 ).
Biologic. A case in which digitalis in serum samples is detected, as determined by a commercial laboratory.
Therapeutic levels of digoxin are 0.5--2.0 ng/mL therapeutic levels of digitoxin are 10--30 ng/mL ( 47 ).
Because multiple determinants exist for digoxin poisoning and serum digoxin concentrations overlap between symptomatic and asymptomatic patients, use of the therapeutic range for diagnosis might be misleading. The therapeutic range should be correlated with the clinical findings.
Serum levels might be low after an exposure to plant glycosides, which cross-react imperfectly. In addition, false-positives might be noted for pregnant women and for patients with liver and renal disease ( 46 ).
Environmental. Detection of digitalis in environmental samples, as determined by FDA.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for digitalis exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Elemental White or Yellow Phosphorus
Ingestion of elemental white or yellow phosphorus typically causes severe vomiting and diarrhea, which are both described as &quotsmoking," &quotluminescent," and having a garlic-like odor. Other signs and symptoms of severe poisoning might include dysrhythmias, coma, hypotension, and death. Contact with skin might cause severe burns within minutes to hours ( 48--51 ).
Biologic. No specific test for elemental white or yellow phosphorus is available however, an elevated serum phosphate level might indicate that an exposure has occurred. Although phosphate production is a by-product of elemental phosphorus metabolism in humans, a normal phosphate concentration does not rule out an elemental phosphorus exposure.
Environmental. Detection of elemental phosphorus in environmental samples, as determined by NIOSH, and an elevated phosphorus level in food, as determined by FDA, might also indicate that an exposure has occurred.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for elemental white or yellow phosphorus exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Depending on the concentration of a dermal exposure, affected skin can initially look completely normal but often will become painful and appear pale or white, possibly leading to necrosis. Inhalational poisoning might result in dyspnea, chest pain, stridor, and wheezing. Oral poisoning can result in vomiting (possibly bloody), abdominal pain, and bloody diarrhea ( 52--54 ).
Systemic poisoning might occur after oral, dermal, or inhalational exposure. Systemic signs and symptoms include hypocalcemia and hyperkalemia, which leads to dysrhythmias, seizures, and possibly death.
Biologic. No specific test for hydrofluoric acid is available however, hypocalcemia, hyperkalemia, and an elevated concentration of fluoride in the serum might indicate that an exposure has occurred. Normal serum fluoride levels are &lt20 mcg/L, but levels vary substantially on the basis of dietary intake and environmental levels.
Environmental. Detection of hydrofluoric acid in environmental samples, as determined by NIOSH.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for hydrofluoric acid exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Long-Acting Anticoagulant (Super Warfarin)
After an acute unintentional ingestion of a long-acting anticoagulant, the majority of patients are entirely asymptomatic. After a substantial ingestion of a long-acting anticoagulant, clinical signs of coagulopathy typically occur within 24--72 hours postexposure. Coagulopathy might manifest as epistaxis, gingival bleeding, hematemesis, hematuria, hematochezia, menometrorrhagia, ecchymosis, petechial hemorrhages, intracranial hemorrhages, or bleeding that is not in proportion with the level of the injury ( 55--57 ).
Biologic. The criteria for diagnosis of a long-acting anticoagulant is the presence of one of the following factors:
Prolonged prothrombin time (PT) and international normalized ratio (INR) 24--72 hours after exposure, persisting for weeks to months, as determined by hospital laboratory tests.
Abnormal assays for factors II and VII in patients with unexplained bleeding and a normal PT, partial thromboplastin time, or INR, as determined by hospital or commercial laboratory tests.
Detection of a long-acting anticoagulant (e.g., brodifacoum) in serum, plasma, or urine, as determined by commercial laboratory tests.
Environmental. Detection of a long-acting anticoagulant in environmental samples, as determined by FDA.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for a long-acting anticoagulant exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Mercury (Elemental)
Inhalation exposure is the most typical route of elemental mercury toxicity. Acute toxicity might result in fever, fatigue, and clinical signs of pneumonitis. Chronic exposure results in neurologic, dermatologic, and renal manifestations. Signs and symptoms might include neuropsychiatric disturbances (e.g., memory loss, irritability, or depression), tremor, paresthesias, gingivostomatitis, flushing, discoloration and desquamation of the hands and feet, and hypertension ( 58--61 ).
Biologic. A case in which elevated urinary or whole blood mercury levels (&gt10 µ g/L) ( 20,58 ) exist, as determined by a commercial laboratory. No definitive correlation exists between either blood or urine mercury levels and mercury toxicity.
Environmental. Detection of mercury in environmental samples, as determined by NIOSH or FDA.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for elemental mercury exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Ingestion is the most typical route of exposure to cause toxicity from inorganic mercury. Signs and symptoms might include profuse vomiting and diarrhea that is often bloody, followed by hypovolemic shock, oliguric renal failure, and possibly death. Survivors of acute poisoning or persons chronically exposed to inorganic mercury might develop neurologic, dermatologic, and renal manifestations that might include neuropsychiatric disturbances (e.g., memory loss, irritability, or depression), tremor, paresthesias, gingivostomatitis, flushing, discoloration and desquamation of the hands and feet, and hypertension ( 58,61,62 ).
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for inorganic mercury exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Mercury (Organic)
Although ingestion of organic mercury is the most typical route of organic mercury toxicity, toxicity might also result from inhalation and dermal exposures, particularly with dimethylmercury. Symptoms of toxicity are typically delayed for > 1 month after organic mercury exposure and usually involve the central nervous system. These symptoms might include paresthesias, headaches, ataxia, dysarthria, visual field constriction, blindness, and hearing impairment ( 58,63--66 ).
Biologic. A case in which whole blood mercury levels (&gt10 µ g/L) ( 20,58 ) are detected, as determined by a commercial laboratory. Urine mercury levels are not useful in evaluating organic mercury poisoning.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for organic mercury exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Methyl Bromide
Methyl bromide poisoning primarily occurs after inhalational exposure, but concurrent dermal exposure might also occur. Methyl bromide is an ocular, dermal, and mucous membrane irritant. Onset of symptoms might be delayed 1--48 hours. Symptoms of inhalational exposure are typically cough and dyspnea, which can develop into pneumonitis and pulmonary edema but might be delayed up to 4--5 days. Severe poisoning can result in seizures, coma, and death ( 67--71 ).
Biologic. No specific test for methyl bromide is available however, detection of elevated bromide levels in serum (reference level: 50--100 mg/L) might indicate that an exposure has occurred. Detection of bromide below toxic levels does not rule out methyl bromide poisoning.
Environmental. Detection of methyl bromide in environmental samples, as determined by NIOSH.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for a methyl bromide exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Methyl Isocyanate
Exposure to methyl isocyanate typically occurs through inhalation or dermal absorption. Toxicity might develop over 1--4 hours after exposure. Signs and symptoms of methyl isocyanate typically include cough, dyspnea, chest pain, lacrimation, eyelid edema, and unconsciousness. These effects might progress over the next 24--72 hours to include acute lung injury, cardiac arrest, and death ( 72--75 ).
Biologic. No biologic marker for methyl isocyanate exposure is available.
Environmental. Detection of methyl isocyanate in environmental samples, as determined by NIOSH.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for methyl isocyanate exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Nerve Agents or Organophosphates
Nerve agent or organophosphate toxicity might result from multiple routes of exposure and is a cholinergic syndrome consisting of excess respiratory and oral secretions, diarrhea and vomiting, diaphoresis, convulsions, altered mental status, miosis, bradycardia, and generalized weakness that can progress to paralysis and respiratory arrest ( 76--78 ).
In certain cases, excessive autonomic activity from stimulation of nicotinic receptors will offset the cholinergic syndrome and will include mydriasis, fasciculations, tachycardia, and hypertension.
Biologic. A case in which nerve agents in urine are detected, as determined by CDC or one of five LRN laboratories that have this capacity. Decreased plasma or red blood cell cholinesterase levels based on a specific commercial laboratory reference range might indicate a nerve agent or organophosphate exposure however, the normal range levels for cholinesterase are wide, which makes interpretation of levels difficult without a baseline measurement or repeat measurements over time.
Environmental. Detection of organophosphate pesticides in environmental samples, as determined by FDA. However, a confirmation test for nerve agents in environmental samples is not available.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for nerve agent or organophosphate pesticide exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
After oral ingestion of nicotine, signs and symptoms of nicotine poisoning mimic those for nerve agent or organophosphate poisoning and typically include excess oral secretions, bronchorrhea, diaphoresis, vomiting (common, especially among children), diarrhea, abdominal cramping, confusion, and convulsions. Although tachycardia and hypertension are common, bradycardia and hypotension might also occur as a result of a severe poisoning ( 79,80 ).
Biologic. A case in which increased nicotine or cotinine (the nicotine metabolite) is detected in urine, or increased serum nicotine levels occur, as determined by a commercial laboratory or CDC.
Environmental. Detection of nicotine in environmental samples, as determined by NIOSH or FDA.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for nicotine exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Opioids (Fentanyl, Etorphine, or Others)
Exposure to opioids typically occurs through ingestion but potentially can result from inhalation, if opioids are aerosolized. Clinical effects of opioid poisoning result from central nervous system and respiratory system depression manifesting as lethargy or coma, decreased respiratory rate, miosis, and possibly apnea ( 81,82 ).
Biologic. A case in which opioids are detected in urine, as determined by hospital or commercial laboratory tests. Fentanyl derivatives and certain other synthetic opioids (e.g., oxycodone) might not be detected by routine toxicologic screens.
Environmental. Detection of opioids in environmental samples, as determined by FDA.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for opioid exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Ingestion of paraquat typically results in gastrointestinal illness, including oropharyngeal ulcerations, vomiting, and diarrhea, which might contain blood. Patients might have dyspnea and hemoptysis as a result of pulmonary edema or hemorrhage, which can progress to fibrosis over the course of days to weeks ( 83--85 ).
Biologic. A case in which paraquat in urine, plasma, or serum is detected, as determined by a commercial laboratory.
Environmental. Detection of paraquat in environmental samples, as determined by NIOSH or FDA.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for paraquat exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Phosgene
The majority of exposures to phosgene occur by inhalation. In high concentrations, exposure might lead to symptoms of ocular, nasal, and throat irritation. Lower respiratory irritation is the most consistent finding after phosgene exposure. If one of the following lower respiratory signs and symptoms is reported, the clinical description for phosgene poisoning has been met ( 86,87 ): chest tightness or cough, dyspnea, or pulmonary edema, which might be delayed < 48 hours after exposure.
Biologic. No biologic marker exists for phosgene exposure.
Environmental. Confirmation of phosgene in environmental samples is not available.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for phosgene exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Confirmed. A clinically compatible case in which laboratory tests (not available for phosgene) have confirmed exposure.
Phosphine
The majority of exposures to phosphine occur by inhalation. Severe poisoning might result in multiorgan involvement (e.g., convulsions, cardiac dysrhythmias, and shock). If one of the following lower respiratory signs and symptoms is reported, the clinical description for phosphine poisoning has been met ( 88--91 ): chest tightness or cough, dyspnea, or pulmonary edema, which might have a delayed onset.
Biologic. No biologic marker for phosphine exposure is available. Finding measurable amounts of urinary phosphorus and phosphorus-containing compounds is not a reliable indicator of exposure.
Environmental. Confirmation of phosphine in environmental samples is not available.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for phosphine exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Confirmed. A clinically compatible case in which laboratory tests (not available for phosphine) have confirmed exposure.
Ricin (Ingestion)
Ingestion of ricin typically leads to profuse vomiting and diarrhea, which might be bloody, followed by hypovolemic shock and multisystem organ dysfunction. Weakness and influenza-like symptoms, fever, myalgia, and arthralgia, might also be reported ( 92--95 ).
Biologic. CDC can assess selected specimens on a provisional basis for urinary ricinine, an alkaloid in the castor bean plant. Only urinary ricinine testing is available at CDC for clincial specimens.
Environmental. Detection of ricin in environmental samples, as determined by CDC or FDA. Ricin can be detected qualitatively by time-resolved fluoroimmunoassay (TRFIA) and polymerase chain reaction (PCR) in environmental specimens (e.g., filters, swabs, or wipes).
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for ricin exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Ricin (Inhalation)
Inhalation of ricin typically leads to cough and respiratory distress followed by pulmonary edema, respiratory failure, and multisystem organ dysfunction. Weakness and influenza-like symptoms of fever, myalgia, and arthralgia might also be reported ( 92--95 ).
Environmental. Detection of ricin in environmental samples, as determined by CDC or FDA. Ricin can be detected qualitatively by TRFIA and PCR in environmental specimens (e.g., filters, swabs, or wipes).
Riot-Control Agents
Cutaneous exposures of riot-control agents might produce dermal burns and rash ( 96--101 ). However, the majority of exposures to riot-control agents occur by inhalation. If a rapid onset of the following signs and symptoms occurs, the clinical description for an exposure to a riot-control agent has been met: 1) lacrimation and 2) one respiratory effect (i.e., nose or throat irritation, cough, or suffocation or choking sensation).
Biologic. No biologic marker for exposure to riot-control agents is available.
Environmental. No method is available for detecting riot-control agents in environmental samples.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for riot-control--agent exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Confirmed. A clinically compatible case in which laboratory tests (not available for riot-control agents) have confirmed exposure.
Saxitoxin
Exposure to saxitoxin might cause numbness of the oral mucosa within 30 minutes after ingestion. In severe poisoning, signs and symptoms typically progress rapidly, including parasthesias, a floating sensation, muscle weakness, vertigo, and cranial nerve dysfunction. Respiratory failure and death might occur from paralysis ( 102--106 ).
Biologic. A case in which saxitoxin in urine is detected, as determined by a commercial laboratory.
Environmental. Detection of saxitoxin in ingested compounds or seafood, as determined by a commercial laboratory or FDA.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for saxitoxin exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Sodium Azide
The majority of exposures to sodium azide occur by inhalation. Signs and symptoms of sodium azide poisoning include lethargy or coma (possibly sudden collapse), dyspnea, tachypnea, tachycardia, and hypotension. Nausea and vomiting also might occur, especially after ingestion. Exposure to dust or gas might produce conjunctivitis and nasal and bronchial irritation. Nonspecific laboratory findings include metabolic and lactic acidosis ( 107--108 ).
Biologic. A case in which sodium azide in serum is detected, as determined by a commercial laboratory.
Environmental. Detection of sodium azide in environmental samples, as determined by FDA.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for sodium azide exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Sodium Monofluoroacetate (Compound 1080)
Exposure to sodium monoflouroacetate might cause systemic toxicity by different routes of exposure. Clinical effects usually develop within 30 minutes to 2.5 hours of exposure but might be delayed as long as 20 hours. The predominant manifestations of sodium monoflouroacetate poisoning are metabolic, cardiovascular, and neurologic signs and symptoms. Effects of acute exposure might include metabolic acidosis, hypotension, dysrhythmias, seizures, coma, and respiratory depression ( 109--111 ).
Biologic. No biologic marker for sodium monoflouroacetate is available.
Environmental. Detection of sodium monoflouroacetate in environmental samples, as determined by FDA.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for a sodium monofluoroacetate exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Confirmed. A clinically compatible case with laboratory confirmation from environmental samples.
The major identifying clinical features of strychnine poisoning through ingestion are severe, painful spasms of the neck, back, and limbs and convulsions with an intact sensorium. Symptoms might progress to coma. Tachycardia and hypertension are also common effects ( 112--115 ).
Biologic. A case in which strychnine in urine or serum is detected, as determined by a commercial laboratory.
Environmental. Detection of strychnine in environmental samples, as determined by NIOSH or FDA.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for strychnine exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Confirmed. A clinically compatible case in which laboratory tests of biologic and environmental samples have confirmed exposure.
Sulfuryl Fluoride
Sulfuryl fluoride poisoning usually occurs after inhalational exposure. The predominant manifestations of sulfuryl fluoride poisoning are respiratory irritation and neurologic symptoms. Effects of acute exposure usually include lacrimation, nose or throat irritation, cough, dyspnea, paresthesias, and seizures ( 116--118 ).
Biologic. No specific test for sulfuryl fluoride exposure is available. However, an elevated fluoride concentration in the serum, hypocalcemia, and hyperkalemia might indicate that an exposure has occurred. Normal serum fluoride levels are &lt20 mcg/L but varies substantially on the basis of dietary intake and environmental levels.
Environmental. Detection of sulfuryl fluoride in environmental samples, as determined by NIOSH.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for a sulfuryl fluoride exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Tetrodotoxin
The consumption of toxic amounts of tetrodotoxin results primarily in neurologic and gastrointestinal signs and symptoms. In severe poisoning, dysrhythmias, hypotension, and even death might occur ( 119--120 ). If a rapid onset of one of the following neurologic and gastrointestinal signs or symptoms occurs, the clinical description for tetrodotoxin poisoning has been met: 1) oral paresthesias (might progress to include the arms and legs), 2) cranial nerve dysfunction, 3) weakness (might progress to paralysis), or 4) nausea or vomiting.
Biologic. No biologic marker for tetrodotoxin exposure is available.
Environmental. No method for detection of tetrodotoxin in environmental samples is available commercially.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for tetrodotoxin exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Confirmed. A clinically compatible case in which laboratory tests (not available for tetrodotoxin) are confirmatory.
Ingestion of toxic amounts of thallium might cause gastrointestinal signs and symptoms, most commonly abdominal pain. Subacute symptoms (onset of days to weeks) after a substantial, acute exposure or a chronic exposure to limited amounts of thallium might include severely painful ascending neuropathy, ataxia, seizure, alopecia, and neurocognitive deficits ( 121--123 ).
Biologic. A case in which elevated spot urine thallium levels are detected (reference level: &lt0.5 µ g/L) ( 20 ), as determined by a commercial laboratory.
Environmental. Detection of thallium in environmental samples, as determined by NIOSH or FDA.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for thallium exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Toxic Alcohols
Ingestion of toxic alcohols (methanol, ethylene glycol, or other glycols) might result in symptoms similar to those of ethanol inebriation (vomiting, lethargy, or coma). A high anion gap metabolic acidosis is common. Renal failure is common after ethylene glycol and diethylene glycol toxicity, whereas optic neuritis and visual impairment are unique to methanol toxicity ( 124--127 ).
Biologic. A case in which glycols or methanol in whole blood is detected, as determined by hospital or commercial laboratory tests.
Environmental. Detection of glycols or methanol in environmental samples, as determined by NIOSH or FDA.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for toxic alcohol exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Trichothecene Mycotoxins
Trichothecene mycotoxins might be weaponized and dispersed through the air or mixed in food or beverages. Initially, route-specific effects are typically prominent. Dermal exposure leads to burning pain, redness, and blisters, and oral exposure leads to vomiting and diarrhea. Ocular exposure might result in blurred vision, and inhalational exposure might cause nasal irritation and cough. Systemic symptoms can develop with all routes of exposure and might include weakness, ataxia, hypotension, coagulopathy, and death ( 128 ).
Biologic. Selected commercial laboratories are offering immunoassays to identify trichothecenes or trichothecene-specific antibodies in human blood or urine ( 129--130 ). However, these procedures have not been analytically validated and are not recommended.
Environmental. Detection of trichothecene mycotoxins in environmental samples, as determined by FDA.
As a result of indoor air-quality investigations involving mold and potentially mold-related health effects, mycotoxin analyses of bulk environmental samples are now commercially available through environmental microbiology laboratories in the United States ( 131 ). Studies have not been done to determine the background level of trichothecenes in nonmoldy homes and office buildings or nonagricultural outdoor environments. Therefore, the simple detection of trichothecenes in environmental samples does not invariably indicate an intentional contamination.
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for trichothecene mycotoxins exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
Vesicant (Mustards, Dimethyl Sulfate, and Lewisite)
The most common clinical effects after exposure to vesicants include dermal (skin erythema and blistering), respiratory (cough, dyspnea, pneumonitis, and acute lung injury), ocular (conjunctivitis and burns), and gastrointestinal (vomiting) signs and symptoms. The effects of the majority of vesicants manifest rapidly (within minutes). However, clinical findings might be delayed for hours after exposure (e.g., sulfur mustard) ( 132--135 ).
Biologic. A case in which sulfur mustard in biologic samples is detected, as determined by CDC or one of five LRN laboratories that have this capacity, and a case in which nitrogen mustard and lewisite are detected in biologic samples, as determined by CDC.
Environmental. Confirmation of the detection of vesicants in environmental samples is not available.
Suspected. A case in which a potentially exposed person is being evaluated by health-care workers or public health officials for poisoning by a particular chemical agent, but no specific credible threat exists
Probable. A clinically compatible case in which a high index of suspicion (credible threat or patient history regarding location and time) exists for vesicant exposure, or an epidemiologic link exists between this case and a laboratory-confirmed case.
When illness results from an intentional or unintentional chemical release (either known or suspected on the basis of a credible threat) into the environment, uniform reporting is paramount for directing appropriate resources, assessing the extent of morbidity and mortality, tracking poisoned persons, and monitoring response to intervention. The case definitions presented in this report facilitate uniform reporting of illness resulting from a chemical (i.e., toxin and toxicant) release.
Health-care providers should report suspected cases of intentional chemical exposure to their local poison-control center (telephone: 800-222-1222) and to a public health agency. Local and state public health officials should notify CDC and law enforcement officials if they identify persons who they suspect have been exposed to intentional chemical poisoning.
The authors acknowledge contributions from Sandra V. McNeel, DVM, and Henry A. Anderson, MD, both with CSTE.
Cells adhere to flat surfaces through focal adhesions, which are integrin-based contacts between the cell and the extracellular matrix[1–3]. Focal adhesions consist of more than 150 proteins with about 700 interactions[4, 5]. Collectively they are known as the adhesome[6]. These proteins have been systematically classified in the adhesome project, which is accessible at www.adhesome.org. Many of the identified molecules are related to signaling[7], including signaling through the small GTPases Rac and Rho to the actin cytoskeleton. While Rho controls focal adhesion assembly and the concomitant formation of contractile stress fibers in the actin cytoskeleton[8], Rac was identified to be foremost responsible for the polymerization of an actin lamellipodium at a protruding cell edge and thus for the formation of nascent adhesions and focal complexes which typically assemble behind the protruding edge[9]. The main isoforms are RhoA and Rac1. GTPases are further regulated by guanine exchange factors (GEFs) and GTPase-activating proteins (GAPs). For the whole Rho-family, more than 130 different GEFs and GAPs have been reported[10]. The pathways of Rac and Rho have been modeled before in different contexts, for example circular dorsal ruffles[11], stress fiber contraction[12], membrane protrusion[13] or stress fiber alignment[14]. Rac is mainly acting through WAVE and Arp2/3 to activate polymerization of actin into dendritic networks required for protrusion. Rho promotes actin polymerization via the formin mDia1 and at the same time promotes myosin II contractility through ROCK and MLCP[15]. In general it is believed that Rac and Rho mutually inhibit each other[16–18], although recent data indicates a more complicated situation depending on the detailed temporal and spatial coordination of Rac and Rho within the cell[19].
Focal adhesions are not only signaling hubs, they also provide the mechanical linkage between the extracellular matrix and the actin cytoskeleton. For this purpose, they contain a large range of different connector proteins, including talin, vinculin, paxillin, and α-actinin. The spatial structure of focal adhesions has been extensively studied with fluorescence microscopy[20, 21], revealing a layered structure dictated by the interplay of flat substrate and plasma membrane. The integrin layer is anchored in the extracellular matrix and therefore relatively immobile. The actin layer moves from the cell periphery towards the cell center driven by actin polymerization at the leading edge and myosin II contractility closer to the cell body. The connector layer moves backwards with the actin cytoskeleton, albeit with a reduced speed due to the effective friction with the underlying integrin layer. Although a more detailed picture of the spatial organization is still missing, recent advances with cryoEM[22], iPALM[23, 24] and dual objective STORM[25] provide increasing insight. A schematic sketch of the situation of interest is given in Figure1.
Schematic presentation of focal adhesions. Schematics of the situation of interest. (A) Cartoon of an adherent cell. During spreading and migration the cell adheres to ligands of the extracellular matrix (ECM), for example fibronectin, at the leading edge through nascent adhesions. They develop into focal complexes in the lamellipodium (LP), which can then mature into focal adhesions in the lamella (LM). Focal adhesions are typically connected to stress fibers that either run from one focal adhesion to another (ventral stress fibers) or end in the actin network (dorsal stress fibers). (B) Enlarged view of a focal adhesion with the main molecular components. The transmembrane protein integrin binds to the fibronectin on the ECM. The connection to the actin stress fibers, which can contract due to the myosin II motor molecules, is made by talin. This basic mechanical link is enhanced by proteins like vinculin, paxillin, or α-actinin.
Focal adhesions are the result of a complex maturation process, which is strongly related to the overall spatial coordination in an adherent cell[26]. Nascent adhesions are thought to nucleate by integrin clustering underneath the lamellipodium, which is a relatively narrow region (1-3 μ m) at the cell periphery characterized by fast retrograde flow (≈25 nm/s) of rapidly polymerizing dendritic actin[27–29]. Towards the cell center, these nascent adhesions grow into focal complexes (FXs), which are sub-micron and typically round adhesions. Distal to the cell periphery, the lamellipodium gives way to the lamella, a relatively extended region characterized by more condensed actin structures, most prominently actin bundles contracted by myosin II motors[30]. Here the retrograde flow speed is reduced to ≈ 2 nm/s[28]. At the lamellipodium-lamella boundary, focal complexes either decay or become stabilized into mature focal adhesions (FAs)[31, 32], which are micron-sized adhesion contacts typically elongated in the direction of the cell body.
The maturation of FXs into FAs has been shown to depend on the presence of physical force[33–37]. It is also strongly related to changes in molecular composition, in particular the recruitment of connector proteins such as vinculin and paxillin[38]. The correlation between force and maturation can be measured experimentally using traction force microscopy[34, 39–41] and suggests that molecular checkpoints exist that ensure that FAs are only assembled if strong attachment is achieved. In 1978 Bell proposed that the rupture rate of a molecular bond under force is proportional to e ( F / F 0 ) , where F is the force acting on this bond and F0 an internal force scale of the order of pico-Newtons[42]. Thus, a higher force leads to a shorter lifetime. Bonds that follow this law have been termed slip bonds. It was believed that in general receptor-ligands pairs are slip bonds, although it has been pointed out that theoretically bond dissociation might also decrease under force[43]. During the last decade, several such catch bonds have been identified[44–46]. Most importantly in our context, the integrin-fibronectin bond has been shown to behave as catch bond[47]. This molecular feature might has evolved as part of the stabilization response of matrix adhesions under force. Because matrix adhesions are expected to consist of a mixture of different types of bonds, the two extreme scenarios would be pure slip bond versus pure catch bond behavior. Depending on their exact molecular composition, it is conceivable that adhesion clusters in different cell types, under different culture conditions and at different times of the maturation process behave more like slip bond or more like catch bond systems.
Focal adhesions are not only important for cell adhesion, but also for cell migration, division, and fate. Being essential for cell migration, they are key elements for many physiological and disease-related processes, including wound healing[48] and metastasis[49]. Recently they have been argued to be essential also for development[50] and stem cell differentiation[51]. There is a large range of possible mechanosensitive processes being involved at focal adhesions, including stress-sensitive ion channels, force-induced opening of cryptic binding sites and large-scale reorganization of the adhesions. For a systems level understanding of focal adhesions, it is mandatory to develop systematic procedures to assess the role of the different adhesome components.
One technique capable of such a systems level approach is the systematic use of RNA-interference (RNAi)[52–54]. In recent years RNAi-screens have become a standard tool in systems biology, as it allows us to dissect complex processes such as migration[55], division[56, 57], or infection[58–60] in regard to the underlying molecular processes. The basic principle of RNAi is the following. Double stranded small interfering RNA (siRNA), which has a length of 21-23 nucleotides, is added to the cell using a variety of methods, for example by microinjection, electroporation or viral gene transfer[54]. During the following assembly of the RNA Induced Silencing Complex (RISC), the siRNA is separated into two strands, the guide strand and the passenger strand. The passenger strand is not needed any more and is degraded, whereas the guide strand is loaded onto the RISC complex. The siRNA-RISC complex then binds to the complementary target messenger RNA (mRNA). The bound target mRNA is degraded and released from the siRNA-RISC complex, which can then again bind other mRNA. The degraded mRNA can no longer be translated into proteins, and thus, the concentration of the protein is reduced in the cell. Until the maximum knockdown is achieved it typically takes 24-72 hours[61]. The stability of the knockdown depends mostly on the stability of the protein but also on factors like cell division rate or the degradation rate of the used siRNA. Therefore, the period of maximal knockdown can vary considerably.
First siRNA-screens have also been conducted for focal adhesions. In[62] numerous morphological features of cells and focal adhesions were analyzed and quantified for multiple siRNA. Here, it was suggested that several gene knockdowns caused similar effects and that many of the morphological features are strongly correlated. Recently a follow-up screen[63] highlighted the effect of specific knockdowns on the cell polarization response together with changes in focal adhesion formation and cell traction force. The authors suggest that both cell contractility and mechanosensing through focal adhesions are controlled by molecular checkpoints that regulate cell polarization.
In order to systematically and quantitatively understand the experimental results with their often counterintuitive relations, theoretical models for focal adhesions are required. In the literature several models for the force-mediated dynamics of focal adhesions have been proposed[32, 64–69]. However, very few models make a connection to the molecular composition as revealed by the adhesome project. The compositional aspects of focal adhesions are represented best by kinetic models with a sufficiently large number of species. Such a model is the clutch model by Macdonald et al.[70]. In that model the focal adhesion is reduced to a three component model modeling the layered structure of the focal adhesions, representing integrin, actin, and a connector molecule that might be identified with e.g. talin. The temporal maturation of FXs into FAs is represented by modeling a hierarchical assembly in which these components successively assemble into a larger complex, which finally gets activated by force. For our purpose, such an approach is ideal to be expanded to include the effect of RNAi. However, because the clutch model focuses on the assembly aspect of focal adhesions, for a more comprehensive approach it has to be extended to include also the effect of signaling at focal adhesions.
Different models have been suggested to model the effect of RNAi. A very global view has been introduced by Bartlett & Davis, who published a model that consists of twelve ordinary differential equations[71]. They give a detailed description of not only the mRNA concentration and the protein concentration, but also take into account phenomena like extracellular transport, cellular uptake, cell division, and the subsequent reduction in siRNA concentration. Parameters were taken from the literature or were estimated. Their model has been verified by comparing the model's results with a variety of in vitro data from the knockdown of luciferase. Apart from this global approach, several models have been suggested which focus on the core function of RNAi. Recently a systematic comparison of such model approaches has been conducted by Cuccato et al.[72]. They compared four of these coarse-grained models[73–75] with experiments conducted at human embryonic kidney cells. Fitting the models' parameters to the experimental data suggested that the model originally proposed by Khanin & Vinciotti[74] fits best. This model is a purely phenomenological one that is based on a standard Hill-type kinetic model. A special feature of this model is that it saturates for high siRNA concentrations, which reflects the experimental findings by Cuccato et al. The most probable explanation for this effect is that the RISC-complexes (and/or other RNAi-associated complexes) are saturated with siRNA[76].
Here we introduce a kinetic model based on the clutch model by Macdonald et al.[70] which allows us to address many of the central questions related to RNAi of focal adhesions. We extend the original model to also describe translation and degradation of proteins, signaling to the actin cytoskeleton, and the detailed effect of force. Our paper is structured as follows. We first explain the model in the Methods section. In the Results and discussion section we discuss the dynamics of the system and the effect of RNAi on focal adhesions. With an analysis of the system dynamics we highlight the three different time scales present in the system. We then discuss more specific applications and extensions of our model. Finally a sensitivity analysis of the model enables us to pinpoint the effects of different knockdowns. We end with a short conclusion and with an outlook to possible future extensions of our model, especially in regard to spatial organization.
We first studied a situation wherein each new task is introduced at a randomly chosen location in characteristic space that is at a distance equal to 1.8ε2 away from any one of the tasks that had to be previously performed. So, in terms of its interaction characteristics, the newly introduced task has some similarity with previous tasks. Our simulation results (Fig. 2) show that WCI evolve as a mechanism for mediating functional specificity as the number of tasks that organisms have to perform to function properly increases (or organisms become more complex). Furthermore, as organisms evolve to perform more tasks, the proportion of the tasks that they carry out via WCI increases (Fig. 2). These results are consistent with the observation that this mechanism for mediating functional specificity is prevalent in multicellular organisms. One reason that WCI evolved as a mechanism for biological specificity is because this allows similar tasks to be performed with some of the same cooperating components, and therefore, the number of genes required for organisms to function properly becomes less than the number of tasks to be performed (Fig. 2). This is consistent with the observation that proteins with similar IDRs (and even the same proteins) are involved in regulating different genes and in forming condensates at different super-enhancers. The same is true for components that form condensates to mediate other biological functions in the cytoplasm and the nucleus. We have carried out calculations with different levels of correlation between new and old tasks (i.e., values of task-task distance other than 1.8ε2), and the qualitative behavior of our model is unchanged (SI Appendix, Fig. S4) unless the new tasks become totally uncorrelated.
WCI evolve as organisms become more complex. This figure shows the variation of the average number of genes in organisms and the number of tasks specifically done via WCI between gene products as the number of tasks required for an organism to function properly increases (or organisms become more complex). The number of tasks performed by single gene products is also shown. When the number of tasks equals 10, 33% of tasks are done via WCI, and when the number of tasks equals 40, this proportion is 56%. Three characteristics describe the interaction characteristics of tasks and gene products.
One implication of the results described so far is that as a greater proportion of tasks are performed via WCI (as the number of tasks increases), the extent to which gene products are cross-reactive to multiple tasks also increases. The results in Fig. 3A show that this is indeed the case. However, the cross-reactivity is limited to similar tasks. This can be seen clearly by considering a situation where a newly introduced task can either be closely related to one of the previous tasks or not. If new tasks that are related to at least one previous task are introduced more frequently than tasks that are unrelated (75% chance for a new task to be at a distance 1.8ε2 away from a previous task and 25% chance to be at least at a distance 3.0ε2 away from all previous tasks), the tasks will be distributed in characteristic space as disjoint groups of related tasks (Fig. 3B). One group may correspond to regulation of gene transcription another could be signaling through SH2/SH3 domains in the cytoplasm. Fig. 3B illustrates that gene products that act via WCI are cross-reactive to a limited set of tasks that are closely related. Quantitatively, the number of tasks that are performed by the same gene products acting cooperatively rapidly declines as the interaction characteristics of the tasks become less related (Fig. 3C).
Limited cross-reactivity accompanies the evolution of WCI. (A) Variation of the extent of cross-reactivity with the evolution of WCI. The x axis shows the number of tasks done by the same cluster of gene products, and the y axis is the percentage of such clusters that are preforming two, three, four, and five tasks in this cross-reactive fashion. (B) Snapshot of simulation results when new tasks are introduced such that they are either closely related to tasks from an earlier era or not. Two modules of such related tasks are depicted in characteristics space. Large spheres with radius ε2 are drawn around each task. Brown spheres show tasks being performed by single-gene products, blue spheres show closely related tasks being performed by clusters of cooperating gene products. Small spheres correspond to gene products. (C) The percentage of two tasks completed by the same gene products is high only for related tasks. Three characteristics describe the interaction characteristics of tasks and gene products.
Some cross-reactivity for similar tasks is an inherent property of the above cooperative model, but the extent of cross-reactivity is limited as otherwise task specificity would be lost. In cells, other mechanisms can be coupled to multivalent WCI to limit cross-reactivity. For example, master transcription factors bind with lock–key type specificity to particular DNA binding sites. Only then can interactions between transcription factor IDRs and that of transcriptional coactivators, chromatin remodelers, and RNA Polymerase II occur through multivalent WCI if specific upstream signals have modified the IDRs to have a valency exceeding a threshold. However, the coactivators, chromatin remodelers can exhibit some cross-reactivity (as in Fig. 3) to regulate related functions, such as genes bound by different master transcription factors. The degree of cross-reactivity could also be limited by topological barriers such as chromosomal domains or localization in subcellular compartments. However, the cross-reactivity that accompanies the evolution of WCI for biological specificity could, when altered by mutation or modification, cause serious pathologies. For example, protooncogenes can be activated when DNA rearrangements create a fusion protein that targets transcriptional activation domains in their vicinity (20, 21). Also, cellular states that generate abnormally large condensates (22) formed by multivalent WCI could sequester high levels of client proteins important for the normal functioning of other genes.
Multivalent WCI as a mechanism underlying biological specificity are prevalent in many organisms across metazoa. We wondered whether the emergence of this mechanism makes organisms more evolvable, thus explaining why it has been repeatedly positively selected and its more prominent role in multicellular organisms. The properties of more evolvable systems (1) include the following: (i) Reduced constraints in maintaining old functions when a new function has to be evolved and (ii) fewer mutations required to produce novel phenotypic traits. Thus, to explore this question, we calculated the time required for organisms to evolve to perform the tasks required for proper function after a new task is introduced. We compared the results of simulations of our model to one where WCI are not allowed i.e., regardless of the similarity between the interaction characteristics of gene products, they are not allowed to act in concert to perform tasks with functional specificity. As Fig. 4 shows, the model allowing the evolution of WCI exhibits shorter response times and requires fewer mutations to respond to new tasks. Increasing values of ε3 also make mutations increasingly less likely to be lethal when WCI are allowed (SI Appendix, Fig. S8). This is because a deleterious mutation in any one gene product involved in mediating functional specificity via multivalent WCI is less likely to result in loss of function (task not performed) compared with the effect of a similar mutation for lock–key interactions. We conclude that the evolution of WCI for functional specificity confers increased and robust evolvability to organisms, as they can evolve to perform new tasks while maintaining old functions with fewer mutations and increased tolerance to deleterious mutations. This result is reinforced by a recent report demonstrating rapid evolution of human IDR proteins (23). Notice that evolvability emerges in our model without violating causality, i.e., this mechanism evolves based on past selection forces and not a pathological knowledge of the future.
The evolution of WCI for biological specificity makes organisms more evolvable. (A) The response time for the organisms to evolve to function properly after a new task is introduced is shown as a function of the number of tasks (or complexity). Results are shown for both the full model and one wherein cooperative interactions between gene products is not allowed. (B) The number of mutations (which includes gene mutation, duplication, and loss) that the average organism needs to acquire to function properly after a new task is introduced is shown as a function of the number of tasks (or complexity). Results are shown for both the full model and one wherein cooperative interactions between gene products is not allowed.
The qualitative results that we have described hold if there is no fitness advantage associated with an organism performing a task poorly (λ1 equals zero in Eq. 1). The only difference is that the response times for organisms to evolve to perform new tasks increase (SI Appendix, Fig. S3). That is, the system becomes less evolvable if there is no fitness advantage for performing tasks poorly. This is because the lack of ability to be positively selected while performing tasks poorly constrains the mutational trajectories that have to be followed to perform new tasks while not abrogating old functions. A similar observation has been made in laboratory experiments following the mutational pathway of a kinase as it evolves to catalyze a new substrate (24). Mutations are first observed in the kinase's allosteric pocket resulting in conformational flexibility that enables it to act on the old and new substrates suboptimally. Then, a mutation in the catalytic site is acquired to change specificity. A similar effect has also been described during the evolution of cross-reactive antibodies during germinal center reactions (25).
Financial support of the Fonds der Chemischen Industrie (Frankfurt/Main), DAAD (Bonn) and Svenska Institutet (Stockholm) is gratefully acknowledged.
Here we will shortly describe the computer-generation procedure of the artifical sequences, which have the same length and nearly the same base distribution as the corresponding natural DNA-sequence ( 8–10).
(i) One chooses an appropriate interval width Di, which is kept constant during the whole generation of the artifical sequence. Typical Di-value vary between 20 and 1000 bp.
(ii) The natural DNA-sequence is divided into consecutive DNA-peaces of length Di.
(iii) Determine the relative ocurrence of all four bases (A, T, C and G) in one DNA-peace of length Di.
(iv) The base distribution acts as input for a computer program, which creates a randomly generated nucleotide series of length Di. The main part of the program is a random number generator see below.
(v) Repeat steps (iii) and (iv) for all DNA peaces of length Di.
(vi) Concatenate all generated nucleotide series in the correct order to give the artifical sequence.
Different random number generators can be found in standard references like ( 14). The results of this paper are obtained with the routines called ran1, ran2 and ran3 of ref. 14 as well as the routine called urng of ref. 15 and the shuffeled nested Weyl-sequence algorithm of ref. 16. All these random number generators produced almost identical results in the present study.
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