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United States Department of Agriculture

Agricultural Research Service

Research Project: APPLICATION OF BIOLOGICAL AND MOLECULAR TECHNIQUES TO THE DIAGNOSIS AND CONTROL OF AVIAN INFLUENZA AND OTHER EMERGING POULTRY PATHOGENS

Location: Exotic and Emerging Avian Viral Diseases Research Unit

Title: Helping poultry and people through research on high pathogenicity avian influenza

Author
item Swayne, David

Submitted to: American Veterinary Medical Association Abstract
Publication Type: Abstract Only
Publication Acceptance Date: April 1, 2009
Publication Date: July 11, 2009
Citation: Swayne, D.E. 2009. Helping poultry and people through research on high pathogenicity avian influenza [abstract]. Convention Notes. 146th American Veterinary Medical Association Annual Convention, July 11-14, 2009, Seattle, Washington. 2009 CDROM.

Technical Abstract: Avian influenza (AI) viruses are a diverse group divided into 144 different subtypes based on different combinations of the 16 hemagglutinin and 9 neuraminidase subtypes, and two different pathotypes (low [LP] and high pathogenicity [HP]). Low pathogenicity avian influenza (LPAI) viruses are maintained in wild birds, and must be adapted to pass to domestic poultry. High pathogenicity avian influenza (HPAI) viruses arise in poultry and historically have not gone back to wild birds. Twenty-seven epidemics of HPAI have occurred in the world since 1959. The largest of these outbreaks has been the H5N1 HPAI which has caused problems in poultry and wild birds in 61 countries in Asia, Europe and Africa since 1996. These viruses have also caused severe infections and death in a few humans. Most frequently, the HPAI viruses were transmitted to humans by direct close contact with infected poultry, although a few cases have implicated consumption of raw duck blood. The Asian H5N1 HPAI virus has readapted to some wild bird species creating a new mechanism of spread. The Asian H5N1 HPAI virus has spread into northern and western Asia, and Europe and Africa, with evidence of involvement of migratory birds, but poultry and their products are still the primary way the virus is moved. Control of H5N1 HPAI in poultry has implications for One Medicine: One Health though preventing exposure, infections and disease in wild birds, pet animals and humans. Vaccines have been applied in some outbreaks to reduce H5N1 HPAI virus spread and control the economic impact of the disease through two critical aspects: 1) vaccine efficacy, and 2) vaccination effectiveness. Vaccine efficacy encompasses the safety and purity of the vaccine, having sufficient antigenic content to produce robust protective immune response, and a sufficiently close genetic match to protect from minor genetic drift. Protection is primarily based on an antibody response to the hemagglutinin (HA) protein and is specific to an HA subtype. Vaccination effectiveness involved all aspects of application of vaccines from storage to administration. When properly applied, high quality AI vaccines will protect poultry by increasing resistance to infection, preventing illness and mortality, reduce the number of infected birds, and if infected, greatly reduce the amount and time that virus is shed from respiratory and alimentary systems. This translates into reduction in environmental contamination or viral load by AI virus and thus reduced transmission. However, vaccination alone will not eradicate AI. Vaccination should only be used as one tool in a comprehensive control program that includes enhanced biosecurity, increased surveillance, education of poultry workers, and elimination of infected poultry. Prior to 2003, vaccines against AI had limited, individual country or regional use in poultry. In late 2003, H5N1 HPAI spread from China to multiple Southeast Asian countries, and to Europe during 2005 and Africa during 2006, challenging governments and all poultry production sectors to seek alternatives to stamping-out programs to control and eradicate AI. AI vaccines have emerged as a new tool for use in comprehensive HPAI control strategies. Historically, AI vaccines have been based on field outbreak strains of the same hemagglutinin subtype grown in embryonating chicken eggs, chemically inactivated, emulsified and administered by parenteral injection. Protection has been primarily the result of an antibody response to the HA protein and is specific to an HA subtype. Recently fowl poxvirus and avian paramyxovirus type 1 (ND) virus vectored vaccines with AI H5 gene inserts have been developed, licensed and used. Two main critical aspects affect vaccine success in an AI control program: 1) vaccine efficacy, and 2) vaccination effectiveness. Vaccine efficacy encompasses the safety and purity of the vaccine, having sufficient antigenic content to produce robust protective immune response, and a sufficiently close genetic match of the hemagglutinin to protect from minor genetic drift. Vaccination effectiveness involved all aspects of application of vaccines from storage to administration. When properly applied, high quality AI vaccines will protect poultry by increasing resistance to infection, preventing illness and mortality, reduce the number of infected birds, and if infected, greatly reduce the amount and time that virus is shed from respiratory and alimentary systems. This translates into reduction in environmental contamination or viral load by AI virus and thus reduced transmission to birds and humans. Vaccines can be used as part of an emergency control program during an active outbreak or can be used routinely if AI is endemic in the region. An archive vaccine bank for H5 and H7 AI can be of value great value in emergency program. However, vaccination alone will not eradicate AI. Vaccination should only be used as one tool in a comprehensive control program that includes enhanced biosecurity, increased surveillance, education of poultry workers, and elimination of infected poultry. The Eurasian-African H5N1 HPAI virus has caused an unprecedented epizootic affecting mainly poultry, but has crossed multiple species barriers to infect captive and wild birds, carnivorous mammals and humans. Human infections have been associated with direct or indirect contact with live or dead poultry while in carnivores, consumption of infected birds or their products have been associated with infections. Experimental studies were conducted in mammals to better understand the modes of exposure that favor transmission of the H5N1 HPAI virus. Of the four mammalian models examined, the ferret and pig demonstrated transmission of H5N1 HPAI virus by oral or direct digestive tract exposure and most closely mimicked human infections and disease, but production of infection by oral or direct digestive tract exposure required a much higher dose of virus than exposure via the upper respiratory tract. The predominate site of virus replication following oral consumption of H5N1 virus infected meat was the respiratory tract, initiated through infection of tonsil followed by nasal cavity infection, but with A/Vietnam/1203/04 (H5N1) strain in ferrets, simultaneous infection also occurred via the upper digestive tract with spread to liver and pancreas. Five H5N1 and one H7N3 HPAI viruses in infected meat caused infection in ferrets following oral consumption, but production of such infections was dependent on virus strain and the amount of virus in the meat. Cooking or pasteurization was effective at killing the virus. These results suggest consumption of infected raw poultry products could produce human infections based on the ferret model. However, the risk or probability of producing such infections would be greatly influenced by several factors. First, because most ethnic groups consume cooked poultry and general education programs have taught complete cooking of poultry, most humans are unlikely to consume uncooked or undercooked poultry. A more likely scenario for transmission through consumption of uncooked poultry would be feeding of infected scraps to carnivorous mammals. Second, if a person were to consume uncooked or undercooked poultry, a high dose would be needed to produce an infection. A greater potential for human infection would be through direct airborne exposure to infected birds or processing of infected birds. This emphasizes the need for early detection of HPAI infected poultry and their destruction before entry into slaughter process. Considering the rarity of human AI cases associated with eating raw infected products and the ease with killing AIV by cooking, AI has not become a food safety issue.

Last Modified: 4/23/2014
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