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FIGURE 3-2 Influenza A Virus Host Range. Of the 17 subtypes of influenza A viruses isolated to date, the majority have come from aquatic birds. In the figure above, white figures indicate instances where the viruses have established permanent lineages, and black figures indicate where sporadic viral infection has occurred. Of the 17 subtypes of the influenza A virus, only the H1, H2, and H3 subtypes have caused pandemics in humans. Subtypes H5, H7, and H9 transmit sporadically to humans but to date have not established permanent lineages or been transmitted between humans. Subtypes of the influenza A viruses have also caused infections in pigs. The H7 subtype has caused infection and established a permanent lineage in horses. This indicates that avian H7 viruses have successfully established lineages in mammals. Recently, the H17 subtype has been described in bats.
SOURCE: Courtesy of Robert G. Webster, St. Jude Children’s Research Hospital.



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