Submitted to: Developments in Biologicals
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2005
Publication Date: 1/31/2006
Citation: Senne, D.A., Suarez, D.L., Stallnecht, D.E., Pedersen, J.C., Panigrahy, B. 2006. Ecology and epidemiology of avian influenza in North and South America. Developments in Biologicals. 124:37-44.
Interpretive Summary: Avian influenza virus is normally found in wild birds, including ducks and shorebirds. The virus typically does not cause disease in these species and virus can be detected all year long. Avian influenza, however, can spread from wild birds to chickens and turkeys, which often results in a disease outbreak. In the United States live bird markets (LBMs) have been shown to be a common way chickens can be infected with avian influenza viruses. These markets provide a source of live birds for the consumer to select for food. The markets bring together birds from many farms, and this increases the risk of introducing avian influenza into our domestic poultry species. Since the markets are seldom free of birds and new birds are introduced on a routine basis, the virus can be maintained in these markets. Several outbreaks in large poultry farms have been traced to viruses present in the market system. Outbreaks of sever disease called highly pathogenic avian influenza is rare, but it has occurred in Canada, the U.S., and Chile in the last three years. These outbreaks have been controlled by eradication of the infected birds.
Technical Abstract: Wild waterfowl and shorebirds are known to be the natural reservoir for influenza A viruses. Surveillance studies in waterfowl and shorebirds in North America show that influenza A viruses are repeatedly recovered from these birds. However, the virus recovery is influenced by geography, season, age and species of birds. In addition to the natural reservoir, the live-bird marketing system (LBMS) in certain regions of United States has been recognized as a man-made reservoir of influenza viruses and has been linked to several outbreaks of low pathogenicity avian influenza (LPAI) in poultry. Outbreaks of LPAI in commercial poultry is attributed to movement of infected birds, dirty or improperly cleaned crates, and contaminated vehicles from the LBMS to poultry farms. However, in the majority of outbreaks in poultry, the source of infection is suspected to be wild aquatic birds or the source in unknown. Since 2002, three outbreaks of highly pathogenic avian influenza (HPAI) have occurred in the Americas; one each in Chile (H7N3), United States (H5N2), and Canada (H7N3). In each of these outbreaks, a precursor virus of low pathogenicity mutated to become highly pathogenic after circulating in poultry. The HPAI viruses recovered from the three outbreaks had unique molecular and phenotypic characteristics that do not conform to other known HPAI viruses. These findings emphasize the need for monitoring wild and domestic bird species for presence of influenza A viruses.