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). |
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H3N2 Infects birds and mammals, including
people. One of the causes of seasonal influenza in people (see
Wikipedia). |
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H3N8 Infects birds, horses and dogs (see
Wikipedia). |
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H5N1 The cause of "bird flu" in humans.
Infects a wide variety of birds and also some mammals (see
Wikipedia). |
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H5N9 Infects birds. |
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H6N2 Infects birds and can be
particularly virulent in poultry. |
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H7N1 Infects birds such as poultry. |
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H7N7 Infects humans, birds, pigs, seals
and horses (see
Wikipedia). |
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H9N2 Infects birds, including poultry. |
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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
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