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Orthomyxoviridae (ὀρθός, orthós, Greek for "straight"; μύξα, mýxa, Greek for "mucus")[1] is a family of negative-sense RNA viruses. It includes seven genera: Alphainfluenzavirus, Betainfluenzavirus, Deltainfluenzavirus, Gammainfluenzavirus, Isavirus, Thogotovirus, and Quaranjavirus. The first four genera contain viruses that cause influenza in vertebrates, including humans, birds (see also avian influenza), and other mammals. Isaviruses infect salmon; the thogotoviruses are arboviruses, infecting vertebrates and invertebrates, such as ticks and mosquitoes.[2][3][4] The Quaranjaviruses are also arboviruses, infecting arthropods as well as birds.

The four genera of Influenza virus that infect vertebrates, which are identified by antigenic differences in their nucleoprotein and matrix protein, are as follows:

This is a genus that was classified in 2016, the members of which were first isolated in 2011.[48] This genus appears to be most closely related to Influenza C, from which it diverged several hundred years ago.[49] There are at least two extant strains of this genus.[50] The main hosts appear to be cattle, but the virus has been known to infect pigs as well.

Viability and disinfection

Mammalian influenza viruses tend to be labile, but can survive several hours in mucus.[51] Avian influenza virus can survive for 100 days in distilled water at room temperature, and 200 days at 17 °C (63 °F). The avian virus is inactivated more quickly in manure, but can survive for up to 2 weeks in feces on cages. Avian influenza viruses can survive indefinitely when frozen.[51] Influenza viruses are susceptible to bleach, 70% ethanol, aldehydes, oxidizing agents, and quaternary ammonium compounds. They are inactivated by heat of 133 °F (56 °C) for minimum of 60 minutes, as well as by low pH <2.[51]

Vaccination and prophylaxisVaccines and drugs are available for the prophylaxis and treatment of influenza virus infections. Vaccines are composed of either inactivated or live attenuated virions of the H1N1 and H3N2 human influenza A viruses, as well as those of influenza B viruses. Because the antigenicities of the wild viruses evolve, vaccines are reformulated annually by updating the seed strains.

When the antigenicities of the seed strains and wild viruses do not match, vaccines fail to protect the vaccinees. In addition, even when they do match, escape mutants are often generated.

Drugs available for the treatment of influenza include Amantadine and Rimantadine, which inhibit the uncoating of virions by interfering with M2, and Oseltamivir (marketed under the brand name Tamiflu), Zanamivir, and Peramivir, which inhibit the release of virions from infected cells by interfering with NA. However, escape mutants are often generated for the former drug and less frequently for the latter drug.[52]

See also