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Influenza A virus

Life > viruses > Negative Strand RNA Viruses > unassigned order > Orthomyxoviridae > Genus: Influenzavirus A

Infects mainly birds but also mammals, including humans.

Subtypes

Influenza type A viruses are classified into subtypes based on the type of two proteins on the surface of the viral envelope:

  • Hemagglutinin (H) is a protein that causes red blood cells to clump together (agglutinate). There are 17 known types of Hemagglutinin.

  • Neuraminidase (N) is an enzyme that cleaves the glycosidic bonds of the monosaccharide sugar, neuraminic acid. There are 9 known types of neuraminidase.

Theoretically, there are 153 different combinations possible of these proteins. However, only some of these combinations have been recorded as subtypes of Influenza type A. The following are important:

H1N1

The cause of "swine flu" in humans in 2009. Some strains only infect humans, others are specific to pigs and yet others are specific to birds. The 1918 - 1919 flu pandemic, termed "Spanish flu" was caused by a strain of H1N1. In the region of 50 - 130 million people died in this pandemic, making it one of the deadliest natural disasters in human history (see Wikipedia).

 

H3N2

Infects birds and mammals, including people. One of the causes of seasonal influenza in people (see Wikipedia).

 

H3N8

Infects birds, horses and dogs (see Wikipedia).

 

H5N1

The cause of "bird flu" in humans. Infects a wide variety of birds and also some mammals (see Wikipedia).

 

H5N9

Infects birds.

 

H6N2

Infects birds and can be particularly virulent in poultry.

 

H7N1

Infects birds such as poultry.

 

H7N7

Infects humans, birds, pigs, seals and horses (see Wikipedia).

 

H9N2

Infects birds, including poultry.

 

Avian influenza

Subtypes and forms of Influenza A viruses that infect birds are referred to as avian influenza (AI). All H5 and H7 AI strains are notifiable to the World Animal Health Organization (Office International des Epizooties). Avian Influenza strains are able to

Links

Publications

  • Becker WB. 1966. The isolation and classification of Tern virus: Influenza virus A/Tern/South Africa/1961. J. Hyg., Camb. 64: 309-320. pdf

Text by Hamish G. Robertson