Group Group V ((−)ssRNA) Scientific name Influenzavirus b: Rank Genus | Family Orthomyxoviridae Higher classification Orthomyxoviridae | |
Similar Influenza A virus subtype, Herpes B virus, Haemophilus | ||
Influenzavirus b
Influenzavirus B is a genus in the virus family Orthomyxoviridae. The only species in this genus is called Influenza B virus.
Contents
Influenza B viruses are only known to infect humans and seals, giving them influenza. This limited host and range is apparently responsible for the lack of Influenzavirus B-caused influenza pandemics in contrast with those caused by the morphologically similar Influenzavirus A as both mutate by both antigenic drift and reassortment. Currently there are two co-circulating lineages of the Influenza B virus based on the antigenic properties of the surface glycoprotein hemagglutinin. The lineages are termed B/Yamagata/16/88-like and B/Victoria/2/87-like viruses. The quadrivalent influenza vaccine licensed by the CDC is currently designed to protect against both co-circulating lineages and has been shown to have greater effectiveness in prevention of influenza caused by influenza B virus than the previous trivalent vaccine.
Further diminishing the impact of this virus "in man, influenza B viruses evolve slower than A viruses and faster than C viruses". Influenzavirus B mutates at a rate 2 to 3 times slower than type A. It is currently accepted that influenza B viruses cause significant morbidity and mortality worldwide, and significantly impacts adolescents and schoolchildren.
Morphology
The Influenza B virus capsid is enveloped while its virion consists of an envelope, a matrix protein, a nucleoprotein complex, a nucleocapsid, and a polymerase complex. It is sometimes spherical and sometimes filamentous. Its 500 or so surface projections are made of hemagglutinin and neuraminidase.
Genome structure
The Influenza B virus genome is 14548 nucleotides long and consists of eight segments of linear negative-sense, single-stranded RNA. The multipartite genome is encapsidated, each segment in a separate nucleocapsid, and the nucleocapsids are surrounded by one envelope.