Classification of DNA viruses that infect humanFamily VirionstructureGenom structure CharacteristicsHepadnaviridae lipid-contain.envelope1 molecule, mainlyds DNA but with asingle strand gapHepatitis B virusParvoviridae Non-enveloped1 molecule,ss DNAoutbreaks of gastroenteritisfollowing eating of shellfishPapillomaviridaePolyomaviridaeNon-enveloped1 molecule, circulards DNAhuman papilomaviruses(genital and oral carcinomas)Adenoviridae Non-enveloped1 molecule, dsDNAHuman: infections of respira-tory and the intestinal tracts,of the eyes; Animals: tumorsHerpesviridae envelopedwith surfaceprojections1 molecule,ds DNA herpes simplex virus,cytomegalovirusPoxviridae enveloped;large, brick-shapedds DNA, covalentlyclosed endssmallpox virus, vacciniavirus
DNA VIRUS REPLICATION STRATEGIESViral genomes contain information which:ensures replication of viral genomesensures packaging of genomes into virionsalters the structure and/or function of the host cell to a greater or lesser degreeVIRAL STRATEGYViral strategy refers to the manner in which each virus carries out the abovefunctions. Since a virus is an intracellular parasite, it has to operate withinlimits imposed by the host cell, or circumvent these limitations.GeneralThe virus needs to make mRNAs that can be translated into protein by the hostcell translation machinery.The virus needs to replicate its genome.Host enzymes for mRNA synthesis and DNA replication are nuclear (except forthose in mitochondrion) and so, if a virus is to avail itself of these enzymes, itneeds to enter the nucleus.
Nuclear DNA virusesParvoviridaePapillomaviridaePolyomaviridaeAdenoviridaeHerpesviridaeCytoplasmic DNA virusesPoxviridaeThis means that they must provide their own mRNA and DNAsynthetic machinery.
PAPILLOMAVIRUS FAMILYThe Papillomavirus family wasformerly grouped with thePolyomavirus family into thePapovavirus family (PApilloma,POlyoma, simian VAcuolating virus 40)because members of both families havea similar structure.However, it is now clear that the twofamilies have a very differentreplication strategy and so each grouphas now been given its own familystatusPROPERTIES OFPOLYOMAVIRUSES ANDPAPILLOMAVIRUSESThey are small: 40 - 60nmThey are icosahedral: majorcapsid protein is VP1, withlesser amounts of VP2, VP3They are non-envelopedThey have circular, double-stranded DNA is associatedwith cell histones (nucleosomes)Papilloma virus
POLYOMAVIRUSESThese include SV40, BK, JC andpolyoma viruses.All have a similar strategy forDNA replication.They are small (~40nmdiameter), icosahedral, non-enveloped viruses that replicatein the nucleus. Depending on thehost cell, they can eithertransform the cell or replicatethe virus and lyze the cell.SV40 virus, a polyoma virus
ADENOVIRUSESgot their name from theadenoidal tissues(tonsils) in which theywere first identified (in1953 W.Rowe andcollaborators).
MORPHOLOGYSize – 70-90 nmShape - icosahedral. Theirmorphogenesis occurs in the cellnucleus, where they alsoaggregate to form large crystalsTheir genome is a linear, dsDNAType of symmetry - cubicNaked.Capsid consist of 252 capsomers
ANTIGENIC STRUCTURE OFADENOVIRUSES4 soluble antigens are knownHexon – A antigen –commonfor all serotypes, is the mainstructural protein of virion(51%)Penton – B antigen – causesearly toxic effect ofadenoviruses to the tissueculture (9 % of all proteins ofvirion)Appendix, filament – Cantigen – causesagglutination of erythrocytes(5 %)P antigen – inner protein –releases after destroying ofthe virion
CLASSIFICATIONFamily Adenorividaegenera:1 Mammaliadenovirusembracing adenoviruses of humans and mammalsspecies:49 pathogenic for human;24 – for monkey;9 – for cattle;2-6 - for horses, sheep, dogs, mice2 Aviadenovirus including adenoviruses of birds.species: 9 pathogenic for cheek;3 – for goose3 –for turkey-cockAbout 130 species (serotypes) of adenoviruses are known
ASSEMBLYAssembly of adenovirus particles occurs in the nucleus.DNA enters the particles after immature capsids are formed. Thecapsids then undergo a maturation process, after which the cellslyse and virions leak out.More structural proteins are made than are needed and excessstructural proteins accumulate in the nucleus where they forminclusion bodies.Adenoviruses code for their own DNA polymerase and DNApackaging proteins.However, although adenoviruses code for their own DNApolymerase, they use host factors in addition to viral proteins forDNA replication, and they use host RNA polymerase and RNAmodification systems and so nucleic acid synthesis needs to be inthe nucleus.
Diagrammatic representation of the uptakeand uncoating of adenovirus particles.Adapted from Zinsser Microbiology 20th Ed.
CLASSIFICATION ACCORDING TO THEANTIGENIC STRUCTURE (TO THE ABILITYTO AGGLUTINATE THE RED BLOOD CELLS)1 subgroup – adenoviruses, which agglutinate monkey’serythrocytes (3,7,11,14,16,20,21,25,28)2 subgroup – adenoviruses which agglutinate white rat’serythrocytes completely(8,9,10,13,17,19,22,23,24,27,29,30)3 subgroup – adenoviruses which agglutinate white rat’serythrocytes partially(1,2,4,5,6,12,18,31)
CLASSIFICATION ACCORDING TO THEONCOGENIC-ABILITYSubgroup A – greatly oncogenic (types 12,18,31)Subgroup B weakly oncogenic (types 3, 43, 7, 8, 11, 14,16, 21)Subgroup C and D – non oncogenic ( all other types)
CULTIVATION- grow in tissue cells of human beings, monkeys andother animals.Most susceptible are subinoculated epithelial cells НеLа,КВ, Нер-2, etc., in which the cytopathogenic effect isrelatively manifest. The inoculated tissue culture areincubated at 37º C for 14 days.- Are non pathogenic for laboratory animals- Do not grow on chick embryo membranes.
CYTOPATHOGENIC EFFECTThe process of cell degenerationconsists of two phases.During the first phase changes inthe cells are induced by toxin-like factors (initial phase ofdegeneration), while in thesecond phase viruses multiplywithin the nucleus andcytoplasm (final phase ofdegeneration).Inclusion bodies from within thenucleus. They consist of virionswhich produce aggregates ofcrystalline structure. Adenovirusmultiplication is accompanied byaccumulation of excess lacticacid in the tissue culture.Normal (not infected) НеLа cells (1);cytopathic effect of adenoviruses onHeLа cells (2)
PATHOGENESIS AND CLINICALPICTUREAdenoviruses cause a variety of diseases, which may occursingly or concurrently. The most important are infections of theupper (sometimes lower) respiratory tracts, the eyes, and theintestinal tract.Adenoviruses can persist for months in the regional lymph nodesor tonsils until they are reactivated.The clinical picture of the disease does not strictly depend uponthe type of adenovirus. One and the same variant may produce awide variety of forms of the disease. The ability of variousserovars to produce one the same disease has also beenascertained.
Infections of the respiratory tract take the form of rhinitis orabacterial pharyngitis, depending on the virus type as well aspresumably on the disposition of the patient.The eye infections may occur alone but are often concurrent withpharyngitis, range from follicular conjunctivitis to a form ofkeratoconjun-ctivitis that may even cause permanent partial lossof eyesight.The intestinal infectionsAn important aspect of the intestinal infections is that the primarygastroenteritis forms are caused by the viral strains 40 and 41,which are difficult to culture.
ADENOVIRUS- CLINICAL SYNDROMES (COMPILED)EpidemicKeratocon-junctivitisHeadache, conjunctivitisfollowed by keratitis,preauricular lymphnodes8, 19,372-7, 14, 15,19, 37Acutefollicular/HemorrhagicconjunctivitisChemosis, follicles,subconjunctival hemorrhage,preauricular lymph nodes11AcuteHemorrhagiccystitisBlood in urine (macroscopichematuria) fever, dysuria11, 4, 7,1, 2134, 35Gastro-enteritis Diarrhea especially in children<4 years oldLow grade fever40-42,31, 25-28,3, 7, 2, 9,12, 13, 18
LABORASTORY DIAGNOSISMethodsRapid:Microscopy: electron;immuno-fluorescent;Virological:Isolation of viruses in tissue culture (HeLa, Hep -2, KB);Indication by CPE, IFT, CFT, ELISA, RIA;Identification by NT, HIT with monky’s and white rat’s red bloodcellsSerological - is mainly used for epidemiologic studiesOther detection methods in current use include polymerase chainreaction and nucleic acid probes.
PreventionHandwashingContact precautions, respiratory precautions in health care settingsAdequate chlorination of swimming poolsSterilization / disinfection of ophthalmologic equipment and use ofsingle dose vials of ophthalmic medicationsVaccine: live, enteric coated, oral vaccine (types 4, 7, 21)ImmunityThe majority of newborn infants possess passive immunity whichthey lose at the age of 6 months.Susceptibility prevails at the age from 6 months to 5 years.Children older than 5 years of age possess antibodies and rarelycontract adenoviral diseases. A relatively low diseases incidenceamong adults is due to immunity acquired following an acute orasymptomatic form of the disease.The immunity is type-specific in character.
HERPESVIRIDAE FAMILYHerpes viruses are a leading cause of human viraldisease, second only to influenza and cold viruses.They are capable of causing overt disease or remainingsilent for many years only to be reactivated, for exampleas shingles.The name herpes comes from the Latin herpes which,in turn, comes from the Greek word herpein whichmeans to creep. This reflects the creeping or spreadingnature of the skin lesions caused by many herpes virustypes.
Enveloped icosahedral virus180 - 200nm;Linear, double-stranded DNAThe space between theenvelope and the capsid is thetegument. This containsvirally-encoded proteins andenzymes involved in theinitiation of replicationCapsid contains 162 doughnutshaped capsomeres.
Antigenic structureThe virus contains twoantigens:the V-antigen, may bedetect in NTand the S-antigen(soluble) – may bedetect in CFT, isallergen
There are at least 25 viruses in the familyHerpesviridae (currently divided into three sub-families).Eight or more herpes virus types are known to infectman frequently
Subfamily Genera Species pathogenicfor humanDiseasesAlphaherpesvirinaeSimplexvirus HSV 1HSV 2KeratoconjunctivitisHerpes labialis, herpesgenitalis neonatal herpes,encephalitisVaricellovirus Varicella-ZostervirusVaricella, herpes zosterILTV-like virus InfectionlaryngotracheitisvirusInfection laryngotracheitisBetaherpesvirinaeCytomegalovirus Cytomegalovirus Cytomegalovirus infectionRoseolovirus Human herpes virus6A (HHV-6A)Human herpes virus6B (HHV-6B)Human herpes virus7-HHV-7Tropism to T-lymphocytesExanthema subitum(roseola infantum)Exanthema subitumHERPESVIRIDAE FAMILY VIRUSESPATHOGENIC FOR HUMAN
Gamma-herpesvirinaeLymphocryptovirusEpstein-Barr virus(EBV)Mononucleosis, Burkitt’slymphoma, Nasophayngealcarcinoma, Lymphoma inimmunodeficient personsRhadinovirus Kaposi’s sarcoma-associated herpesvirus(HHV-8)Cercopiteci (monkey)herpes virus type BKaposi’s sarcomaCause acute respiratorydiseases at human
CULTIVATION1) on the chorioallantoic membrane of the chick embryo(12-13 days old) on which it forms inflammatorynecrotic foci.2) on embryonal lung and kidney tissues of humanorrgin and in cultures of НеLа cells, Detroit-6 cells, etc.2 type of CPE may be observe (at the same time):(a) – foci of proliferation (which consist of some layers ofoval cell);(b) – multinuclear syncytium.3) on laboratory animals. In case of intra cerebruminoculation – encephalitis evolves; in case of inoculationinto the cornea - cerato-conjunctivitis will develop.
HERPES VIRUS REPLICATION
PATHOGENESISThe virus infects epithelial mucosal cells or lymphocytes.- then travels up peripheral nerves to a nucleated neurone where it may stayfor years followed by reactivation. A reddened area gives rise to a maculawhich crusts to form a papula. The fluid in this blister is full of virus. As longas the virus is kept moist it can remain infectious.HSV-1 and HSV-2 first infect cells of the mucoepithelia or enter throughwounds. They then frequently set up latent infections in neuronal cells. The siteof the initial infection depends on the way in which the patient acquires thevirus.Once epithelial cells are infected, there is replication of the virus around thelesion and entry into the innervating neurone. The virus travels along theneurone (by a process called retrograde transport) to the ganglion(ex.trigeminal or sacral ganglia).
The virus can also travel in the opposite direction to arriveat the mucosa that was initially infected. Vesiclescontaining infectious virus are formed on the muscosaand the virus spreads. The vesicle heals and there isusually no scar as a result.Herpes simplex 1 and 2 can infect both humans and otheranimals but only humans show symptoms of disease.Both types of HSV can also persistently infectmacrophages and lymphocytes. The presence of thevirus is often indicated by the formation of syncytia andinclusion bodies in the nucleus.
CLINIC FORMS OF HERPESINFECTION- Primary and RecurrentPrimary herpes is the result of infection by direct contact or by theair-droplet route.herpetic fever or, less frequently, as herpes simplex.(an increase of temperature to 39-40°С, severe headache, meningealsymptoms, vomiting, hyperaemia of the conjunctivas, andinflammation of the lymph nodes. On the following day аvesicular eruption usually appears on the lips, the temperaturefalls, and the disease takes the course of herpes simplex.Initial infection with herpes simplex type 1 usually occurs in earlychildhood. The portal of entry is normally the oral mucosa (“oraltype”) and the infection usually manifests as a gingivostomatitis.The initial infection with HSV type 2 normally affects theurogenital area (“genital type”) and can be contracted despite anexisting HSV type 1 infection.Herpes recurrence is frequently encountered with certain diseases(malaria, influenza, acute catarrhal conditions, lobar pneumonia,meningitis, intoxications, psychic disorders), traumas, and
VARICELLA-ZOSTER VIRUS (ALSO KNOWNAS HERPES ZOSTER VIRUS, HUMAN HERPESVIRUS-3)Zoster means girdle from the characteristic rash that forms a beltaround the thorax in many patients.The structure of Varicella virus is very similar to Herpes Simplexvirus although the genome is somewhat smallerThis virus causes two major diseases, chicken-pox (Varicella),usually in childhood, and shingles, later in life.Shingles (Zoster) is a reactivation of an earlier varicella infection.
CHICKENPOXThe patient is the source of infection.The causative agent is spread by the air-droplet route.The patient is infectious from the last days ofincubation and to the time the crusts fall off.The incubation period lasts from 2 to 3 weeks.PathogenesisThe portals of entry are the nasopharyngeal space andthe conjunctiva. From there, the virus undergoes aviremic phase in which it is transported by the blood tothe skin, where the typical exanthem is produced.Eruption ceases on the fifth day of the disease.
SYMPTOMS OF CHICKEN POXRash is pleomorphic, monolocular, appears withtemperature anywhere on the body, but usually first onthe back, than the face, head, mouth, main body andarms and legs (never on palms and foots).The lessions appear at different times and within a day orso go through a characteristic evolution from macule topapule to vesicle to crusts (without scars).
HERPES ZOSTER (SHINGLES)- is reactivation of varicella.It can occur at any age, but becomes increasingly common withadvancing age.It begins with pain in the area supplied by a nerve of sensation,often on the chest or abdomen, but sometimes on the face, orarm or leg. After a few days to two weeks the characterisc rashof varicella appears along the course of the nerve. The rashsubsides within a week, but pain may persist for weeks ormonths.
TreatmentAs with HSV, acyclovir (or other nucleoside analogs) canbe useful, particular in preventing dissemination inimmunosuppressed patients.Varicella immunoglobulin can also be used. Normally,however, only supportive care is used in children whoquickly recover if they mount an adequate cell-mediatedresponse.VaccineThere is a live attenuated vaccine virus and this is used inthe United States. It leads to antibody production and cell-mediated immunity. It can be used post-exposure.
LABORATORY DIAGNOSISRapid methods: specimens – smears from mucous membranes, m-lfrom vesicles and other rash-elements, biopsy specimens from thelesions :- IFT (direct and indirect);- electronic microscopy;- studying slides stained by Romanovsky’s or by Morozov’stechnics (to detect intra nuclear inclusions)2. Virological method: specimens - smears from mucous membranes,m-l from vesicles and other rash-elements, cerebro-spinal fluid,blood, scrape from cornea- obtaining: in tissue culture; on chorion-allantois membrane ofchick embryo; on labоratory animals- detection: - by CPE; characteristic cytopathic effects (plaque)including multinucleated cells- by HAT
Herpes simplex 1:Histological stain. Note themultinucleate cell with darkstaining inclusions3. Allergic test – by on cutaneoustest4. Biological method (look atvirological – cultivation onlab.animals)5. Serological method: serum inserologic tests: NT, CFT, PHAT,IFT, IHAT.
EPSTEIN- BARR VIRUS(GAMMAHERPESVIRINAE)Epstein-Barr virus is the causative agent of Burkittslymphoma in Africa, nasal pharyngeal carcinoma inthe orient and infectious mononucleosis in the west. Itwas first discovered as the causative agent of Burkittslymphoma and it was later found that patients withinfectious mononucleosis have antibodies that reactwith Burkitts lymphoma cells.The virus only infects a small number of cell types thatexpress the receptor for complement C3d component(CR2 or CD21). These are certain epithelial cells (oro-and naso-pharynx) and B lymphocytes. This explainsthe cellular tropism of the virus.
BURKITTS LYMPHOMAThis is a tumor of the jaw and face found in childrenThis lymphoma is endemic in equatorial Africa but onlyoccurs rarely elsewhere. Why this is so is unclear butthere is probably a genetic reason possibly involving anassociation with malaria. Persons who are resistant tomalaria appear to be susceptible to progression to thelymphoma.
Burkitts lymphoma histological stain.Notice the large multinucleated cells
INFECTIOUS MONONUCLEOSISThe primary infection is often asymptomatic but the patient mayshed infectious virus for many years. Some patients developinfectious mononucleosis after 1-2 months of infection. The disease ischaracterized by malaise, lymphadenopathy, tonsillitis, enlargedspleen and liver and fever. The fever may persist for more than aweek. There may also be a rash. The severity of disease oftendepends on age (with younger patients resolving the disease morequickly) and resolution usually occurs in 1 to 4 weeks.Complications: meningitis, encephalitis, myelitis. Secondaryinfections, autoimmune hemolytic anemia, thrombocytopenia,agranulocytosis, aplastic anemia may also occur.As noted above a chronic syndrome may also occur. Thesymptoms are similar to those reported for chronic fatiguesyndrome (headaches, sore throat and low fever) but EBV isprobably not the cause of chronic fatigue syndrome.
DiagnosisIn infectious mononucleosis, blood smears show the atypicallymphocytes (Downey cells). There are also serological testsavailable. Heterophile antibodies are produced by the proliferatingB cells and these include an IgM that interacts with Paul-Bunnellantigen on sheep red blood cells.Leukemia cells thatcontain Epstein Barrvirus using a FAstaining
CYTOMEGALOVIRUSCytomegalovirus has the largest genome of all herpes viruses andappears only to replicate in human cells. Its name derives form thefact that, like other herpes viruses, it can form multinucleated cells(syncytia) with characteristically staining inclusions. Some cellssuch as macrophages and fibroblasts support a productiveinfection while a latent infection is set up in several cell typesincluding T lymphocytes and stromal cells of the bone marrow.There is only one serotype.
PATHOGENESISCytomegalovirus causes no symptoms in children and at mostmild disease in adults.The virus first infects the upper respiratory tract and then locallymphocytes. Circulating lymphocytes then spread the virus toother lymphocytes and monocytes in spleen and lymph nodes.The virus finally spreads to a variety of epithelial cells includingthose of salivary glands, kidney tubules, testes, epididymis andcervix.Infection is usually asymptomatic (sub-clinical) but glandularfever is sometimes seen in young adults.The virus can inhibit T cell responses. The virus elicits bothhumoral antibodies and cell-mediated immunity but the infectionis not cleared. Cell-mediated immunity, not humoral antibodies,controls the infection
Congenital diseaseThere are two instances in which cytomegalovirus can causeserious disease. During a primary infection of the mother, thevirus can spread via the placenta to the fetus and congenitalabnormalities can occur; in fact, this virus is the most commonviral cause of congenital disease. Up to one in forty newborns inthe United States are infected by the virus. Abnormalities includemicrocephaly, rash, brain calcification and hepatosplenomegaly.These may result in hearing loss (bilateral or unilateral) andretardation. As might be expected, when reactivation occurs in apregnant mother (usually reactivation in the cervix), thesymptoms are less severe because of the mothers seropositivity. Inthis case, congenital abnormalities are rare.Besides infection in utero, infants may be infected perinatally
DiagnosisMost infections are asymptomatic and therefore go undiagnosed.There are fluorescent antibody and ELIZA tests. Multinucleated(cytomegalinic) cells with characteristic inclusions can be seen inbiopsies of many tissues.TreatmentGanciclovir, which inhibits the replication of all human herpesviruses, is usually used, especially to treat retinitis. Foscarnet is alsoapproved in the US. Acyclovir is not effective.A vaccine is being developed but the best way to avoid the virus is torestrict contact between infected children and pregnant women.Also since cytomegalovirus is sexually transmitted, condoms can limitspread.
H&E stain of lung section showing nuclearinclusions with the appearance of an "owlseye". The inclusion is surrounded by a clearhalo that extends to the nuclear membrane.CMV infection can occur without the typicalcytomegalic cells.H&E stain of CMV-infected cells inlung of AIDS patient. Nuclearinclusions can be seen
Specimen of human embryonic lung reveals the presence ofcytomegalovirus using immunofluorescent technique. Mag.25X. CDC/Dr. Craig Lyerla
POXVIRUSES There are several reasons why poxviruses are ofimportance:Certain poxviruses are of historic note, such assmallpox and vaccinia (cow pox, which was usedin the smallpox vaccinePox viruses may be possible agents ofbioterrorismPox viruses are used in new techniques ofvaccine development (such as genetically-engineered vaccinia)Some members of this family infect man(molluscum contagium , monkey pox, cow pox).Note: chicken pox is caused by a herpes viruswhich is not a member of the poxviridae
Possible scheme forthe formation ofinfectious poxvirions. The viruscore becomeswrapped incytoplasmicmembrane and mayescape when thehost cell is lyzed.Some othermembrane-boundvirions may budthrough othermembranes, inwhich case theyhave twomembranes. Ineither case, thevirions areinfectious. Adaptedfrom Baron, S. Ed.Medical Microbiology4th Edition. 1996.