One approach the U.S. Department of Agriculture uses to ensure food security is to conduct research on animal diseases, both at home and abroad. Poultry diseases, for example, continue to threaten the health and production of chickens, turkeys, and other bird species, and some are even a threat to human health.
At the Agricultural Research Service’s Southeast Poultry Research Laboratory (SEPRL) in Athens, Georgia, scientists are pursuing strategies to help prevent and mitigate the impact of important poultry diseases. (See "Reducing the Threat of Exotic Avian Diseases" story this issue.) Their discoveries in the areas of detection, prevention, management, control, and eradication help protect the U.S. poultry industry, which generates about $25 billion and contributes $2.5 billion in exports each year.
SEPRL serves as a major international resource for controlling avian influenza and virulent Newcastle disease. Because of their expertise and research skills, scientists at SEPRL are among the first to be notified when an outbreak of avian influenza occurs here in the United States or in other countries. They rapidly sequence the virus and conduct clinical studies to identify and characterize virus strains and determine their virulence and potential to spread among poultry and people. Importantly, they assess whether our diagnostic tests will be able to detect new and emerging strains and, if needed, develop new tests. SEPRL scientists also make significant contributions to the development of vaccines to ensure that we have the best tools to control domestic or exotic diseases (those from other countries) that pose a threat to the United States.
Although avian influenza is not new to domestic poultry, concerns are growing about outbreaks of emerging strains in Asia and the Middle East that are “zoonotic”—meaning they can be transmitted to humans. Virulent (highly pathogenic) forms of avian influenza cause a high rate of death in birds, and mild forms (low pathogenic) result in respiratory and reproductive problems. There is considerable concern, however, that these mild virus forms might change, or mutate, to the severe forms. And as we just experienced in the spring of 2013 with the H7N9 outbreak in China, even low pathogenic strains can emerge in poultry and acquire the ability to cause severe disease in humans.
One research tool scientists have added to their arsenal to fight disease is “reverse genetics.” The process involves constructing avian influenza viruses with specific genetic sequences to learn how they cause disease in poultry, adapt to new hosts, and acquire the ability to infect humans. Using this technique, SEPRL scientists genetically altered an H7N2 virus that infected birds in the northeastern United States from 1994 to 2006. They found that the virus needed insertions of amino acids at a key site to become virulent. This research improved our understanding of how viruses become virulent and contributed to our ability to predict the risk of low pathogenic viruses changing to the virulent form.
Newcastle disease, which first appeared in the United States in the 1930s, is another major problem that scientists are tackling. Virus strains native to the United States cause only mild symptoms, similar to a common cold for poultry. But exotic strains can cause devastating losses, and new strains are evolving that can threaten U.S. poultry production.
For example, a Newcastle strain traced to pet birds in California hit the poultry industry in the early 1970s. It took more than 2 years to eradicate the disease, at a cost of $56 million in federal funds. In 1992, thousands of infected turkeys in North Dakota were euthanized after virulent Newcastle disease was detected.
As early as the 1940s, scientists had developed vaccines to prevent this disease and had identified strains that produced symptoms ranging from mild to fatal. Exotic Newcastle disease has been eradicated in U.S. poultry, but identifying the cause for differences in the severity in strains remains a challenge.
Because of the limitations of PCR (polymerase chain reaction) tests used to detect emerging Newcastle disease viruses, it is possible that viral transmission could occur undetected among wild birds and poultry. It is impossible to predict which genotypes represent the most significant threat to the U.S. poultry industry. There is a need for further evaluation of the effectiveness of current U.S. vaccines and diagnostic assays for emerging viruses.
ARS partners with other government agencies and scientists worldwide to help manage animal diseases where they first emerge, controlling them at the source before they have a chance to spread to the United States.
As a leader in animal health research, ARS’s main goal is to protect and ensure the safety of the nation’s agriculture and food supply. We continue to do this by delivering scientific information and tools to detect, control, and, when feasible, eradicate animal diseases.
Cyril G. Gay
Senior National Program Leader
Animal Production and Protection
"Forum" was published in the March 2014 issue of Agricultural Research magazine.