A Brief Introduction to the Avian Influenza Virus
The avian influenza (AI) virus is type A influenza isolated from and adapted to an avian host. Type A influenza belongs to the orthomyxovirdae virus family, is enveloped, and is pleiomorphic with a size ranging from 80–120 nm (reviewed in ). Type A influenza strains are classified by the serological subtypes of the primary viral surface proteins, the hemagglutinin (HA) and neuraminidase (NA). The HA has 16 subtypes (H1–H16) and contains neutralizing epitopes. Antibodies against the NA are not neutralizing, and there are nine neuraminidase or “N” subtypes. The “H” and N subtypes seem to be able to assort into any combination, and many of the 144 possible combinations have been found in natural reservoir species, although some combinations are more common than others.
All 16 subtypes have been found in ducks, gulls, or shorebirds, the natural reservoir host species of the virus. However, in these species certain subtypes are more common than others; for example, H3, H4, and H6 are most common in ducks in North America [2, 3] and although there is no clear association between host range or host restriction based on HA subtype, some subtypes are more common in some species than others, i.e., H1 and H3 in swine, H3 in horses, and H5 and H7 in chickens.
Keywordsavian influenza virus type A influenza orthomyxovirus host range pathogenesis molecular characteristics
- 1.1. Lamb, R. A. and Krug, R. M. (2001) Orthomyxoviridae: The viruses and their replication, in Fields Virology, 4th ed. (D. M. Knipe and P. M. Howley, eds.). Philadelphia: Lippincott, Williams and Wilkins, pp. 1487–1532.Google Scholar
- 4.4. Basler, C. F., Reid, A. H., Dybing, J. K., Janczewski, T. A., Fanning, T. G., Zheng, H., Salvatore, M., Perdue, M. L., Swayne, D. E., Garcia-Sastre, A., Palese, P., and Taubenberger, J. K. (2001) Sequence of the 1918 pandemic influenza virus nonstructural gene (NS) segment and characterization of recombinant viruses bearing the 1918 NS genes. Proc. Natl. Acad. Sci. USA 98, 2746–2751.CrossRefPubMedGoogle Scholar
- 12.12. Spackman, E., McCracken, K. G., Winker, K., and Swayne, D. E. (2006) H7N3 avian influenza virus found in a South American wild duck is related to the Chilean 2002 poultry outbreak, contains genes from equine and North American wild bird lineages, and is adapted to domestic turkeys. J. Virol. 80, 7760–7764.CrossRefPubMedGoogle Scholar
- 13.13. Suarez, D. L., Senne, D. A., Banks, J., Brown, I. H., Essen, S. C., Lee, C., Manvell, R. J., Mathieu-Benson, C., Moreno, V., Pedersen, J. C., Panigrahy, B., Rojas, H., Spackman, E., and Alexander, D. J. (2004) Recombination resulting in virulence shift in avian influenza outbreak in Chile. Emerging Infect. Dis. 10, 693–699.PubMedGoogle Scholar
- 16.World Organization for Animal Health, Chapter 2.7.12, Avian Influenza in Manual of Diagnostic Tests and Vaccines for Terrestrial Animals (2004), (2005) http://www.oie.int/eng/normes/mmanual/A_00037.htm
- 18.18. Senne, D. A., Panigrahy, B., Kawaoka, Y., Pearson, J. E., Suss, J., Lipkind, M., Kida, H., and Webster, R. G. (1996) Survey of the hemagglutinin (HA) cleavage site sequence of H5 and H7 avian influenza viruses: Amino acid sequence at the HA cleavage site as a marker of pathogenicity potential. Avian Dis. 40, 425–437.CrossRefPubMedGoogle Scholar
- 21.21. Pasick, J., Handel, K., Robinson, J., Copps, J., Ridd, D., Hills, K., Kehler, H., Cottam-Birt, C., Neufeld, J., Berhane, Y., and Czub, S. (2005) Intersegmental recombination between the haemagglutinin and matrix genes was responsible for the emergence of a highly pathogenic H7N3 avian influenza virus in British Columbia. J. Gen. Virol. 86, 727–731.CrossRefPubMedGoogle Scholar