Source:http://linkedlifedata.com/resource/umls/id/C0029348
NCI: A negative-strand linear single-strand RNA virus with an 8 segment genome. Virions are enveloped and usually spherical or pleomorphic, 50-120 nm in diameter. Influenza B viruses are usually found only in humans. Unlike influenza A viruses, these viruses are not classified according to subtype.,MSH: Species of the genus INFLUENZAVIRUS B that cause HUMAN INFLUENZA and other diseases primarily in humans. Antigenic variation is less extensive than in type A viruses (INFLUENZA A VIRUS) and consequently there is no basis for distinct subtypes or variants. Epidemics are less likely than with INFLUENZA A VIRUS and there have been no pandemics. Previously only found in humans, Influenza B virus has been isolated from seals which may constitute the animal reservoir from which humans are exposed.