Orthomyxoviridae

The family of viruses that contains the 3 genera of influenza viruses, types A and B, C, and “Thogoto-like viruses.” Virions are roughly spherical or filamentous, and the former (the more common form) are 80–120 mm in diameter and ether-sensitive; envelopes are studded with surface projections; nucleocapsids are of helical symmetry, 6–9 nm in diameter, and contain single-stranded, segmented RNA. The nucleoprotein antigen of each type of virus is common to all strains of the type but is distinct from those of the other types; the mosaic of surface antigens varies from strain to strain. Nucleocapsids seem to be formed in the nuclei of infected cells, hemagglutinin, and neuraminidase in the cytoplasm; virus maturation occurs during budding of the cell membrane. Influenza virus types A and B are subject to mutation resulting in epidemics. Influenza virus C differs from types A and B ( e.g., lacks neuraminidase) and belongs to a separate genus. SEE ALSO: Influenza virus.

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Or·tho·myxo·vi·ri·dae .ȯr-thō-.mik-sə-'vir-ə-.dē n pl a family of single-stranded RNA viruses that have a spherical or filamentous virion with numerous surface glycoprotein projections, a helical nucleocapsid, and a genome consisting of six to eight segments of RNA and that include the viruses causing influenza A, influenza B, and influenza C and a genus (Thogotovirus) of tick-borne viruses that occas. infect humans

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Or·tho·myxo·vi·ri·dae (or″tho-mik″so-virґĭ-de) [ortho- + myxo- + virus + -idae] the influenzaviruses: a family of RNA viruses having a pleomorphic virion that may be roughly spherical and 80–120 nm in diameter or filamentous and up to several microns long, consisting of a lipid bilayer envelope with large peplomers, surrounding a helical nucleocapsid. The genome consists of seven (influenza C virus) or eight (influenza A virus and influenza B virus) molecules of linear negative-sense single-stranded RNA (total MW approximately 5 Ч 10⁶, total size 10.0–13.6 kb). Viruses contain seven to nine major polypeptides, including a transcriptase and a neuramidase, and are sensitive to lipid solvents, radiation, and disinfectants. Replication occurs in the nucleus and cytoplasm, and assembly is by budding on the plasma membrane. Genera include Influenzavirus A, Influenzavirus B, Influenzavirus C, and the Thogoto-like viruses.