Orthomyxoviridae

There are four genera of influenza virus, each containing only a single species, or type. Influenza A and C infect a variety of species, while influenza B almost exclusively infects humans, and influenza D infects cattle and pigs.

The type A viruses are the most virulent human pathogens among the three influenza types and cause the most severe disease. Influenza B virus is almost exclusively a human pathogen, and is less common than influenza A. The only other animal known to be susceptible to influenza B infection is the seal.

The serotypes that have been confirmed in humans, ordered by the number of known human pandemic deaths, are:

• H1N1 caused "Spanish flu" in 1918 and "Swine flu" in 2009.

  [13]

• H2N2 caused "Asian Flu".

• H3N2 caused "Hong Kong Flu".

• H5N1, "avian" or "bird flu".

  [14]

• H7N7 has unusual zoonotic potential.

  [15]

• H1N2 is endemic in humans and pigs.

  [citation needed]

• H9N2, H7N2, H7N3, H10N7.