Orthomyxoviridae (ὀρθός, orthós, Greek for "straight"; μύξα, mýxa, Greek for "mucus") 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. The Quaranjaviruses are also arboviruses, infecting arthropods as well as birds.
This is a genus that was classified in 2016, the members of which were first isolated in 2011. This genus appears to be most closely related to Influenza C, from which it diverged several hundred years ago. There are at least two extant strains of this genus. The main hosts appear to be cattle, but the virus has been known to infect pigs as well.
Mammalian influenza viruses tend to be labile, but can survive several hours in mucus. 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. 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.
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.