Basic information about Avian Influenza virus

摘要

Type A influenza viruses can infect several animal species, including birds, pigs, horses, seals and whales. Influenza viruses that infect birds are called "avian influenza viruses." Birds are an especially important species because all known subtypesof influenza A viruses circulate among wild birds, which are considered the natural hosts for influenza A viruses. Avian influenza viruses do not usually directly infect humans or circulate among humans. Influenza A viruses can be divided into subtypeson the basis of their surface proteins — hemagglutinin (HA) and neuramini-dase (NA). There are 15 known H subtypes. While all subtypes can be found in birds, only 3 subtypes of HA (H1, H2 and H3) and two subtypes of NA (Nl and N2) are known to have circulated widely in humans.