Influenzavirus B is a genus in the virus family Orthomyxoviridae. The only species in this genus is called "Influenza B virus".
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.
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 lower than type A. However, influenza B mutates enough that lasting immunity is not possible. For example at the U.S.'s Food and Drug Administration's (FDA) Center for Biologics Evaluation and Research's Vaccines and Related Biological Products Advisory Committee's 101st meeting of February 16, 2005, an extensive discussion and vote was held concerning next year's flu vaccine virus selection including which influenza B strain to use in the formulation of the flu vaccine:
"For Influenza B, the question was asked: are there new strains present? And the answer was yes, and in 2004, the majority of the viruses were similar to a strain called B/Shanghai/361/2002, which is from the so-called B/Yamagata/1688 hemagglutinin lineage. That lineage was not the one that was being used in the vaccine that was current last year. In a minority of the strains that were found during the epidemiological studies were similar to the strain that was in the vaccine for last year, which was B/Hong Kong/330/2001, which belongs to the HA lineage that we represent with the strain B/Victoria/287. In answer to the question were these new viruses spreading, the answer, of course, is definitely yes. The Fujian-like viruses had become widespread around the world and were predominant everywhere, and these B/Shanghai-like strains at the time we were holding this meeting in February were predominant not only in North America and the United States, but also in Asia and Europe."
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.
Nucleic acid 
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.
Sources and notes 
- ^ Osterhaus AD, Rimmelzwaan GF, Martina BE, Bestebroer TM, Fouchier RA (2000). "Influenza B virus in seals". Science 288 (5468): 1051–3. doi:10.1126/science.288.5468.1051. PMID 10807575.
- ^ Hay AJ, Gregory V, Douglas AR, Lin YP (2001). "The evolution of human influenza viruses". Philos. Trans. R. Soc. Lond., B, Biol. Sci. 356 (1416): 1861–70. doi:10.1098/rstb.2001.0999. PMC 1088562. PMID 11779385.
- ^ Matsuzaki Y, Sugawara K, Takashita E, Muraki Y, Hongo S, Katsushima N, Mizuta K, Nishimura H (2004). "Genetic diversity of influenza B virus: the frequent reassortment and cocirculation of the genetically distinct reassortant viruses in a community". J. Med. Virol. 74 (1): 132–40. doi:10.1002/jmv.20156. PMID 15258979.
- ^ Lindstrom SE, Hiromoto Y, Nishimura H, Saito T, Nerome R, Nerome K (1999). "Comparative Analysis of Evolutionary Mechanisms of the Hemagglutinin and Three Internal Protein Genes of Influenza B Virus: Multiple Cocirculating Lineages and Frequent Reassortment of the NP, M, and NS Genes". J. Virol. 73 (5): 4413–26. PMC 104222. PMID 10196339.
- ^ Yamashita M, Krystal M, Fitch WM, Palese P (1988). "Influenza B virus evolution: co-circulating lineages and comparison of evolutionary pattern with those of influenza A and C viruses". Virology 163 (1): 112–22. doi:10.1016/0042-6822(88)90238-3. PMID 3267218.
- ^ Nobusawa E, Sato K (April 2006). "Comparison of the Mutation Rates of Human Influenza A and B Viruses". J Virol 80 (7): 3675–8. doi:10.1128/JVI.80.7.3675-3678.2006. PMC 1440390. PMID 16537638.
- ^ Transcript of U.S. FDA Center for Biologics Evaluation and Research Vaccines and Related Biological Products Advisory Committee's 101st meeting of February 16, 2005. origin.www.fda.gov DOC format Google provided HTML format
- ^ a b Büchen-Osmond, C. (Ed) (2006). "ICTVdB Virus Description - 00.046.0.04. Influenzavirus B". ICTVdB - The Universal Virus Database, version 4. Columbia University, New York, USA. Retrieved 2007-09-15.
External links