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For more information about non-human (variant) influenza viruses that may be transmitted to humans, see Zoonotic influenza
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [2]; Associate Editor(s)-in-Chief: Alejandro Lemor, M.D. [3]
Influenza virus can be classified into 3 main types: A, B and C. Based on the surface glycoproteins, hemagglutinin (HA) and neuraminidase (NA), influenza type A is further classified into several subtypes and can infect many species, including humans. Type B can only infect humans and type C is not common and causes only mild illness.
There are three types of influenza viruses: A, B, and C. Only influenza A viruses are further classified by subtype on the basis of the two main surface glycoproteins hemagglutinin (HA) and neuraminidase (NA). Influenza A subtypes and B viruses are further classified by strains.[1]
Species | Hemagglutinin Subtypes |
Neuraminidase Subtypes |
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Humans | H1, H2, H3, H5, H6, H7, H9, H10 | N1, N2, N6, N7, N8, N9 |
Poultry | H1, H2, H3, H4, H5, H6, H7, H8, H9, H10, H11, H12, H13, H14, H15, H16 | N1, N2, N3, N4, N5, N6, N7, N8, N9 |
Pigs | H1, H2, H3, H4, H5, H9 | N1, N2 |
Bats | H17, H18 | N10, N11 |
Adapted from CDC [2] |
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