page_title: Orthomyxoviridae
section_title: Structure
hierarchical_section_title: Orthomyxoviridae / Structure
caption_attribution_description: English: Schematic structure of influenza A virus (IAV). The envelope of the IAV particle, which is derived from the host cell plasma membrane, contains three trans-membrane proteins; two surface glycoproteins designated as hemagglutinin (HA) and neuraminidase (NA) and the proton channel matrix protein 2 (M2). The matrix protein 1 (M1) underlies the inner surface of the viral envelope and associates with NEP and viral ribonucleoprotein complexes (vRNPs). The eight vRNPs comprise eight negative-strand RNA segments associated with the nucleoprotein (NP) and three RdRp polymerase subunits (PA, PB1, PB2).
context_page_description: Orthomyxoviridae 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 birds, humans, 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.
  The four genera of Influenza virus that infect vertebrates, which are identified by antigenic differences in their nucleoprotein and matrix protein, are as follows:
  Alphainfluenzavirus infects humans, other mammals, and birds, and causes all flu pandemics
  Betainfluenzavirus infects humans and seals
  Deltainfluenzavirus infects pigs and cattle
  Gammainfluenzavirus infects humans, pigs, and dogs.
context_section_description: The influenzavirus virion is pleomorphic; the viral envelope can occur in spherical and filamentous forms. In general, the virus's morphology is ellipsoidal with particles 80 to 120 nm in diameter, or filamentous with particles 80 to 120 nm in diameter and up to 20 µm long. There are some 500 distinct spike-like surface projections in the envelope each projecting 10 to 14 nm from the surface with varying surface densities. The major glycoprotein (HA) spike is interposed irregularly by clusters of neuraminidase (NA) spikes, with a ratio of HA to NA of about 4.5 to 1.
  The viral envelop composed of a lipid bilayer membrane in which the glycoprotein spikes are anchored encloses the nucleocapsids; nucleoproteins of different size classes with a loop at each end; the arrangement within the virion is uncertain. The ribonuclear proteins are filamentous and fall in the range of 50 to 130 nm long and 9 to 15 nm in diameter. They have a helical symmetry.
caption: Influenza A virus structure
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