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Published: 2008
Pages: 7
Author(s): Ella Rowan
Introduction
Avian influenza is caused by viruses that naturally occur in water-associated birds such as ducks, geese, swans, and shorebirds. Avian influenza viruses (AIV) are classified according to two types of proteins present on the surface of the virus, hemagglutinin (H), and neuraminidase (N). There are 16 known hemagglutinin proteins and 9 known neuraminidase proteins, for a total of 144 possible H/N combinations or "subtypes". Virtually every possible H/N subtype has been found in wild birds, and AIV typically do not cause serious disease in these species.
In contrast to wild birds, domestic poultry such as chickens and turkeys can be extremely susceptible to certain strains of AIV. These strains are referred to as "highly pathogenic avian influenza" (HPAI) viruses. The HPAI designation refers only to the severity of disease caused in domestic poultry, and is not related to the potential to cause disease in humans or other species. To date, all known HPAI viruses have been of the H5 or H7 subtypes, although not all H5 and H7 viruses are HPAI viruses. Commercial poultry producers are aware of the potential threat that wild waterfowl present to domestic poultry, and for decades have taken precautions to prevent contact between domestic and wild birds.
On rare occasions, AIV can mutate or recombine with human influenza viruses and become infectious to humans. Beginning in 2005, an increasing number of human cases of influenza caused by an HPAI H5N1 subtype of an AIV were reported in southeast Asia. Prior to that time, infections with this particular virus had primarily been limited to birds. The human cases sparked worldwide concern that this virus could cause another worldwide epidemic ("pandemic") of influenza in humans, such as those experienced in 1918, 1957, and 1968.
As a result of this concern, several wild bird surveillance programs were initiated in Washington to assess the prevalence of AIV in wild birds, and to provide an early warning to poultry producers and public health officials should the HPAI H5N1 virus of concern enter the United States via migratory birds.
The purpose of this report is to summarize AIV sampling efforts and test results from wild birds collected by Washington Department of Fish and Wildlife (WDFW) between July 1st 2007 and June 30th 2008. A brief summary of data collected by other agencies within the state of Washington is also included.