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Types
There are many different subtypes of type A influenza viruses. These subtypes differ because of certain proteins on the surface of the virus (hemagglutinin [HA] and neuraminidase [NA] proteins). Each different combination of HA and NA proteins is a different subtype of the virus.

Infection with certain avian influenza A viruses (e.g., some H5 and H7 strains) can cause widespread disease and death among some species of domestic birds. Since 1997, more than 16 outbreaks of H5 and H7 inf...Read the full article