Antigenic drift

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Antigenic drift is distinct from antigenic shift, which is a different mode of genetic change in viruses.

Antigenic drift[1][2] is the accumulation of mutations in the genetic makeup of the influenza virus. These changes usually occur in the virus's surface proteins. The two main surface proteins, also called antigens, are the hemagglutinin and the neuraminidase. The hemagglutinin is responsible for entry into host epithelial cells while the neuraminidase is involved in the process of new virions budding out of host cells. The host immune response to viral infection is largely determined by the immune system's recognition of influenza antigens (primarily the hemagglutinin).

As in all RNA viruses, mutations in influenza occur frequently because the virus has no way of checking its RNA for errors (the virus' RNA polymerase has no proofreading mechanism). Mutations in the surface proteins allow the virus to elude some host immunity, and the numbers and locations of these mutations that confer the greatest amount of immune escape has been an important topic of study for over a decade[3][4][5].

Antigenic drift has been responsible for heavier-than-normal flu seasons in the past, like the outbreak of influenza A Fujian (H3N2) in the 2003 - 2004 flu season. All influenza viruses experience some form of antigenic drift, but it is most pronounced in the influenza A virus.

Antigenic drift should not be confused with antigenic shift, also called reassortment, which is the process by which two different subtypes of influenza coinfect a single cell and exchange RNA segments to form a new subtype.

Antigenic drift should not be confused with random genetic drift which is a very different but important process population genetics.

[edit] See Also

[edit] References

  1. ^ D. J. D. Earn, J. Dushoff, S. A. Levin (2002). "Ecology and Evolution of the Flu". Trends in Ecology and Evolution 17: 334-340.
  2. ^ A. W. Hampson (2002). “Influenza virus antigens and antigenic drift”, Influenza. Elsevier Science B. V., 49-86.
  3. ^ R. M. Bush, W. M. Fitch, C. A. Bender, N. J. Cox (1999). "Positive selection on the H3 hemagglutinin gene of human influenza virus". Molecular Biology and Evolution 16: 1457-1465.
  4. ^ W. M. Fitch, R. M. Bush, C. A. Bender, N. J. Cox (1997). "Long term trends in the evolution of H(3) HA1 human influenza type A". Proceedings of the National Academy of Sciences USA 94: 7712-7718.
  5. ^ D. J. Smith, A. S. Lapedes, J. C. de Jong, T. M. Bestebroer, G. F. Rimmelzwaan, A. D. M. E. Osterhaus, R. A. M. Fouchier (2004). "Mapping the antigenic and genetic evolution of influenza virus". Science 305: 371-376.

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Topics in population genetics
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Key concepts: Hardy-Weinberg law | genetic linkage | linkage disequilibrium | Fisher's fundamental theorem | neutral theory
Selection: natural | sexual | artificial | ecological
Effects of selection on genomic variation: genetic hitchhiking | background selection
Genetic drift: small population size | population bottleneck | founder effect | coalescence
Founders: R.A. Fisher | J.B.S. Haldane | Sewall Wright
Related topics: evolution | microevolution | evolutionary game theory | fitness landscape | genetic genealogy
List of evolutionary biology topics
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