Evolution of influenza A viruses in wild birds
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Influenza virus surveillance studies in wild bird populations in the
Americas, Europe, and Asia confirmed that wild aquatic birds are the
reservoir for all known influenza A viruses. Phylogenetic analysis
groups the influenza viruses in wild aquatic birds into 2 distinct
superfamilies -- one in the Americas and one in Eurasia. The
separation of viruses into American and Eurasian clades implies that
transmission of HP [highly pathogenic] H5 into the Americas by wild
birds is likely to be a rare event. The rapid evolution of the
Eurasian H5N1 viruses makes them a continued threat to poultry and
humans worldwide.

[Reference: Robert G. Webster, Scott Krauss, Diane Hulse-Post,
Katharine Sturm-Ramirez: Evolution of influenza A viruses in wild
birds. J Wildl Dis 2007 43: S-S6. Abstract
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