Influenza A Virus

Influenza A virus causes influenza in birds and some mammals, and is the only species of influenzavirus A. Influenzavirus A is a genus of the Orthomyxoviridae family of viruses. Strains of all subtypes of influenza A virus have been isolated from wild birds, although disease is uncommon. Some isolates of influenza A virus cause severe disease both in domestic poultry and, rarely, in humans. Occasionally, viruses are transmitted from wild aquatic birds to domestic poultry, and this may cause an outbreak or give rise to human influenza pandemics.

Influenza A viruses are negative-sense, single-stranded, segmented RNA viruses. The several subtypes are labeled according to an H number (for the type of hemagglutinin) and an N number (for the type of neuraminidase). There are 17 different H antigens (H1 to H17) and nine different N antigens (N1 to N9). The newest H antigen type, identified as H17 by researchers, was isolated from fruit bats in 2012.

Each virus subtype has mutated into a variety of strains with differing pathogenic profiles; some are pathogenic to one species but not others, some are pathogenic to multiple species.

A filtered and purified influenza A vaccine for humans has been developed, and many countries have stockpiled it to allow a quick administration to the population in the event of an avian influenza pandemic. Avian influenza is sometimes called avian flu, and colloquially, bird flu. In 2011, researchers reported the discovery of an antibody effective against all types of the influenza A virus.

Read more about Influenza A Virus:  Variants and Subtypes, Annual Flu, Structure and Genetics, In Non-humans, Human Influenza Virus

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Influenza A Virus - Human Influenza Virus - Evolution
... See also Punctuated equilibrium Taubenberger says "All influenza A pandemics since, and indeed almost all cases of influenza A worldwide (excepting human infections from avian viruses such as H5N1 and H7N7), have ... are composed of key genes from the 1918 virus, updated by subsequently incorporated avian influenza genes that code for novel surface proteins, making the ... Researchers from the National Institutes of Health used data from the Influenza Genome Sequencing Project and concluded that during the ten-year period examined, most of the time the hemagglutinin gene ...

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