Influenzavirus B is a genus in the virus

Virus

A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...

 family Orthomyxoviridae

Orthomyxoviridae

The Orthomyxoviridae are a family of RNA viruses that includes five genera: Influenzavirus A, Influenzavirus B, Influenzavirus C, Isavirus and Thogotovirus. A sixth has recently been described...

. The only species in this genus is called "Influenza B virus".

Influenza B viruses are only known to infect human

Human

Humans are the only living species in the Homo genus...

s and seal

Pinniped

Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae .-Overview: Pinnipeds are typically sleek-bodied and barrel-shaped...

s, giving them influenza

Influenza

Influenza, commonly referred to as the flu, is an infectious disease caused by RNA viruses of the family Orthomyxoviridae , that affects birds and mammals...

. This limited host range is apparently responsible for the lack of Influenzavirus B-caused influenza pandemics in contrast with those caused by the morphologically similar Influenzavirus A

Influenzavirus A

Influenza A virus causes influenza in birds and some mammals and is the only species of Influenzavirus A. Influenzavirus A is a genus of the Orthomyxoviridae family of viruses. Strains of all subtypes of influenza A virus have been isolated from wild birds, although disease is uncommon...

 as both mutate by both genetic drift

Genetic drift

Genetic drift or allelic drift is the change in the frequency of a gene variant in a population due to random sampling.The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces...

 and reassortment

Reassortment

Reassortment is the mixing of the genetic material of a species into new combinations in different individuals. Several different processes contribute to reassortment, including assortment of chromosomes, and chromosomal crossover. It is particularly used when two similar viruses that are infecting...

.

Further diminishing the impact of this virus "in man, influenza B viruses evolve slower than A viruses and faster than C viruses

Influenzavirus C

Influenzavirus C is a genus in the virus family Orthomyxoviridae, which includes those viruses which cause influenza. The only species in this genus is called "Influenza C virus".Influenza C viruses are known to infect humans and pigs, giving them influenza...

". 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.

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

's Food and Drug Administration

Food and Drug Administration

The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...

's (FDA) Center for Biologics Evaluation and Research

Center for Biologics Evaluation and Research

The Center for Biologics Evaluation and Research is one of six main centers for the U.S. Food and Drug Administration , which is a part of the U.S. Department of Health and Human Services. The current Director of CBER is Dr. Karen Midthun, M.D...

'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."

Morphology

The Influenza B virus capsid

Capsid

A capsid is the protein shell of a virus. It consists of several oligomeric structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may not correspond to individual proteins, are called capsomeres. The capsid encloses the genetic...

 is enveloped while its virion consists of an envelope, a matrix protein, a nucleoprotein complex, a nucleocapsid, and a polymerase

Polymerase

A polymerase is an enzyme whose central function is associated with polymers of nucleic acids such as RNA and DNA.The primary function of a polymerase is the polymerization of new DNA or RNA against an existing DNA or RNA template in the processes of replication and transcription...

 complex. It is sometimes spherical and sometimes filamentous. Its 500 or so surface projections are made of hemagglutinin and neuraminidase

Neuraminidase

Neuraminidase enzymes are glycoside hydrolase enzymes that cleave the glycosidic linkages of neuraminic acids. Neuraminidase enzymes are a large family, found in a range of organisms. The most commonly known neuraminidase is the viral neuraminidase, a drug target for the prevention of the spread...

.

Nucleic Acid

The Influenza B virus genome is 14648 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.

External links

• Influenza Research Database Database of influenza genomic sequences and related information.
• Viralzone: Influenzavirus B