What is the role of antigenic shift in the pathogenesis of influenza?

Updated: Aug 07, 2020
  • Author: Hien H Nguyen, MD, MS; Chief Editor: Michael Stuart Bronze, MD  more...
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Antigenic shift is less frequent than antigenic drift. In a shift event, influenza genes between 2 strains are reassorted, presumably during coinfection of a single host. Segmentation of the viral genome, which consists of 10 genes on 8 RNA molecules, facilitates genetic reassortment. Because pigs have been susceptible to both human and avian influenza strains, many experts believe that combined swine and duck farms in some parts of Asia may have facilitated antigenic shifts and the evolution of previous pandemic influenza strains.

The reassortment of an avian strain with a mammalian strain may produce a chimeric virus that is transmissible between mammals; such mutation products may contain H or N proteins that are unrecognizable to the immune systems of mammals. This antigenic shift results in a much greater population of susceptible individuals in whom more severe disease is possible.

Such an antigenic shift can result in a virulent strain of influenza that possesses the triad of infectivity, lethality, and transmissibility and can cause a pandemic. Three major influenza pandemics have been recorded:

  • The Spanish influenza pandemic of 1918 (H1N1)

  • The pandemic of 1957 (H2N2)

  • The pandemic of 1968 (H3N2)

Smaller outbreaks occurred in 1947, 1976, 1977, and 2009.

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