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Biosecurity
Previous highly pathogenic outbreaks of AI (HPAI) were thought to be the result of flock exposure to a lowly pathogenic strain of AI (LPAI) and during the infection process the virus mutated to the more detrimental HPAI strain.
The HPAI was then transferred to other farms through breaches in biosecurity appearing as clusters of farm infections in a region. This mode of infection and transmission is still valid.
The current strain of HPAI infection appears to have adapted to wild birds.
Surveillance of migratory bird mortalities has detected the HPAI Eurasia H5N1 in U.S. wild bird populations.
Wild birds with HPAI symptoms have been found along the east coast from northern Canada all the way to Florida.
Surveillance also detected H5N1 positive wild birds in areas around the Ohio, Mississippi, and Missouri Rivers.
Likewise, sporadic, and clustered infections of back yard, hobby, and commercial poultry flocks across the Midwest have been reported.
Figure 1. Wild bird migration routes across North America. Source: U.S. Fish and Wildlife Service
MIGRATION ROUTES
Wild bird migration routes across North America are generally shaped by geography, forming 4 flyways (Atlantic, Mississippi, Central and Pacific).
The increasing day length with the onset of spring stimulates the migration of birds in the southern states to the far northern regions of North America.
Atlantic Flyway that extends from southwest Africa northward through Europe and includes Central Siberia, Greenland, and Canada.
This creates the opportunity for disease to migrate from one continent to another and may explain the presence of Eurasia H5N1 in wild bird populations across the US east coast in 2022.
GREATER SPREAD IN WILD BIRDS
There is concern that AI will further spread in wild bird populations. One area of significant wild bird concentration is the Artic Refuge located in northern Alaska.
It is here that 200 species of wild migratory birds from all 4 US flyways along with the East Asian-Australasian and West Pacific Flyway come together to build nesting sites.
Long days support the growth of forage and insect populations necessary to feed offspring.
The onset of winter drives birds south to warmer environments and forage.
The accumulation of wild birds in the Artic Refuge allows transmission of both LPAI and HPAI within and across species. It is expected ...
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