page_title: Orthomyxoviridae
section_title: Influenza B
hierarchical_section_title: Orthomyxoviridae / Types / Influenza B
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: Influenza B virus is almost exclusively a human pathogen, and is less common than influenza A. The only other animal known to be susceptible to influenza B infection is the seal. This type of influenza mutates at a rate 2–3 times lower than type A and consequently is less genetically diverse, with only one influenza B serotype. As a result of this lack of antigenic diversity, a degree of immunity to influenza B is usually acquired at an early age. However, influenza B mutates enough that lasting immunity is not possible. This reduced rate of antigenic change, combined with its limited host range (inhibiting cross species antigenic shift), ensures that pandemics of influenza B do not occur.
caption: Host range of influenza viruses
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