• A negative-strand linear single-strand RNA virus with an 8 segment genome. Virions are enveloped and usually spherical or pleomorphic, 80-120 nm in diameter. Subtyping is based on the antigenic properties of the hemagglutinin and neuraminidase proteins. Influenza type A viruses can infect people, birds, pigs, horses, and other animals, but wild birds are the natural hosts for these viruses.
  NCI Thesaurus
  U.S. National Cancer Institute, 2021
• Any viral organism that can be assigned to the species Influenza A virus.
  CDISC Terminology
  Clinical Data Interchange Standards Consortium (CDISC), 2021
• One of three types of virus that cause the illness called influenza (flu). The influenza A virus can infect people, birds, pigs, horses, and other animals. It is the main cause of most influenza epidemics.
  NCI Dictionary of Cancer Terms
  U.S. National Cancer Institute, 2021
• The type species of the genus INFLUENZAVIRUS A that causes influenza and other diseases in humans and animals. Antigenic variation occurs frequently between strains, allowing classification into subtypes and variants. Transmission is usually by aerosol (human and most non-aquatic hosts) or waterborne (ducks). Infected birds shed the virus in their saliva, nasal secretions, and feces.
  NLM Medical Subject Headings
  U.S. National Library of Medicine, 2021