Submitted to: United States Animal Health Association Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: November 15, 2006
Publication Date: July 5, 2007
Citation: Swayne, D.E., Suarez, D.L., Pantin Jackwood, M.J., Spackman, E., Kapczynski, D.R., Afonso, C.L. 2007. Why are avian influenza viruses emerging and what tools are needed to prevent and control the infection and disease?. In: Proceedings of the 110th Annual Meeting of the U.S. Animal Health Association, October 12-18, 2006, Minneapolis, Minnesota. p. 728-729. Technical Abstract: Twenty-four epizootics of high pathogenicity avian influenza (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 other birds in 55 countries of 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 HPAI viruses cause severe systemic infection in multiple poultry species and the viruses can be present in multiple internal organs, meat, eggs, and blood. By contrast, low pathogenicity AI (LPAI) viruses cause only a respiratory and intestinal infection without systemic spread. The availability of the real-time RT-PCR test for avian influenza virus (AIV) continues to increase in the National Animal Health Laboratory Network. The test is rapid and sensitive, but it was originally validated for tracheal swabs for chicken and turkeys. However, the test is being used for other sample types and species, and issues of RNA extraction efficiency and PCR inhibitors have been an issue with cloacal swabs and tissue samples. Different methods for extracting RNA have been developed that provide improvements in both areas. A procedure for skeletal and cardiac muscle has been bench validated, and an improved cloacal sample testing is in the process of being bench validated. Additional efforts to use robotics to improve throughput for RNA samples is also in progress. Alternative tests that are commonly used for AIV is the antigen capture ELISA tests (immunoassay). These tests are popular because they are rapid, simple to perform, and require little equipment or training to perform. These tests, although not as sensitive as virus isolation or RRT-PCR, are effective at identifying virus from birds that are sick or dead from AIV. In an effort to reduce cost, it was proposed that 11 tracheal samples should be pooled instead of the usual five samples for flock surveillance. Studies at SEPRL and the University of Delaware (Dr. Jack Gelb) show no loss of sensitivity in experimental samples, but some issues of sample volume and practicality remain. Three AI vaccine technologies show promise for use in the U.S. in the near future against H5 and H7 subtypes. The oldest technology, killed whole virus adjuvanted vaccines, can provide solid protection against clinical disease from HP I virus challenge. Two H5 inactivated AI vaccines in the USDA Vaccine Bank protect chickens against illness and death, and greatly reduces the number of infected birds when challenged with an Asian strain of H5N1 HPAI virus. In addition, when vaccinated birds become infected they shed 2-3 log10 less virus than non-vaccinated chickens. Both vaccines induced strong antibody response as measured by hemagglutination inhibition test. Another licensed technology, recombinant fowlpox-AI-H5 vaccine, was shown to protect chickens against both low and high challenge doses of an Asian H5N1 HPAI virus. Another promising technology is using Newcastle disease (ND) as a vector for AI hemagglutinin protein. In a study using a recombinant Newcastle-AI-H7 vaccine, eye drop vaccination protected chickens from both velogenic ND virus and H7N7 HPAI virus. HPAI viruses cause systemic infection, including replication in skeletal and cardiac muscle. A recent Asian H5N1 virus was used to experimentally challenge 2 week old chickens by a mucosal route of exposure, and groups of birds were sampled every 6 hours to follow with the course of infection. The virus was inconsistently found at 6 and 12 hours, but virus was consistently found in muscle for most birds at every time point after (18-48 hours). In 2006, H5N1 LPAI viruses have been isolated from wild birds from several U.S. states. The sequence analysis shows these viruses are North American origin and have no relation to the Asian H5N1 HPAI viruses.