Transmission of Eurasian avian H2 influenza virus to shorebirds in North America.

Influenza A virus of the H2 subtype caused a serious pandemic in 1957 and may cause similar outbreaks in the future. To assess the evolution and the antigenic relationships of avian influenza H2 viruses, we sequenced the haemagglutinin (HA) genes of H2 isolates from shorebirds, ducks and poultry in North America and derived a phylogenetic tree to establish their interrelationships. This analysis confirmed the divergence of H2 HA into two geographical lineages, American and Eurasian. One group of viruses isolated from shorebirds in North America had HA belonging to the Eurasian lineage, indicating an interregional transmission of the H2 gene. Characterization of HA with a monoclonal antibody panel revealed that the antigenicity of the Delaware strains differed from the other avian strains analysed. The data emphasizes the importance of avian influenza surveillance.