What are the reservoirs for influenza virus?

Updated: Aug 07, 2020
  • Author: Hien H Nguyen, MD, MS; Chief Editor: Michael Stuart Bronze, MD  more...
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In addition to humans, influenza also infects a variety of animal species. More than 100 types of influenza A infect most species of birds, pigs, horses, dogs, and seals. Influenza B has also been reported in seals, and influenza C has been reported, though rarely, in pigs.

Some of these influenza strains are species-specific. The species specificity of influenza strains is partly due to the ability of a given hemagglutinin to bind to different sialic acid receptors on respiratory tract epithelial cells. Avian influenza viruses generally bind to alpha-2,3-sialic acid receptors, whereas human influenza viruses bind to alpha-2,6-sialic acid receptors.

In this context, the term avian influenza (or “bird flu”) refers to zoonotic human infection with an influenza strain that primarily affects birds. Swine influenza refers to infections from strains derived from pigs.

New strains of influenza may spread from other animal species to humans, however. Alternatively, an existing human strain may pick up new genes from a strain that usually infects birds or pigs.

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