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''Influenza B virus'' is the only species in the genus ''Betainfluenzavirus'' in the
virus A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsk ...
family ''
Orthomyxoviridae ''Orthomyxoviridae'' (from Greek ὀρθός, ''orthós'' 'straight' + μύξα, ''mýxa'' 'mucus') is a family of negative-sense RNA viruses. It includes seven genera: ''Alphainfluenzavirus'', ''Betainfluenzavirus'', '' Gammainfluenzavirus'', ...
''. Influenza B virus is known only to infect
human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, cultu ...
s and
seals Seals may refer to: * Pinniped, a diverse group of semi-aquatic marine mammals, many of which are commonly called seals, particularly: ** Earless seal, or "true seal" ** Fur seal * Seal (emblem), a device to impress an emblem, used as a means of a ...
. This limited host range is apparently responsible for the lack of associated
influenza Influenza, commonly known as "the flu", is an infectious disease caused by influenza viruses. Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. These symptom ...
pandemic A pandemic () is an epidemic of an infectious disease that has spread across a large region, for instance multiple continents or worldwide, affecting a substantial number of individuals. A widespread endemic disease with a stable number of in ...
s in contrast with those caused by the morphologically similar
influenza A virus '' A virus'' (''IAV'') causes influenza in birds and some mammals, and is the only species of the genus ''Alphainfluenzavirus'' of the virus family ''Orthomyxoviridae''. Strains of all subtypes of influenza A virus have been isolated from wild ...
as both mutate by both
antigenic drift Antigenic drift is a kind of genetic variation in viruses, arising from the accumulation of mutations in the virus genes that code for virus-surface proteins that host antibodies recognize. This results in a new strain of virus particles that is ...
and
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 particul ...
. There are two known circulating lineages of Influenza B virus based on the antigenic properties of the surface glycoprotein
hemagglutinin In molecular biology, hemagglutinins (or ''haemagglutinin'' in British English) (from the Greek , 'blood' + Latin , 'glue') are receptor-binding membrane fusion glycoproteins produced by viruses in the '' Paramyxoviridae'' family. Hemagglutinins a ...
. The lineages are termed B/Yamagata/16/88-like and B/Victoria/2/87-like viruses. The quadrivalent influenza vaccine licensed by the
CDC The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georg ...
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 humans, 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. Nevertheless, it is accepted that Influenza B virus could cause significant
morbidity A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not immediately due to any external injury. Diseases are often known to be medical conditions that a ...
and mortality worldwide, and significantly impacts adolescents and schoolchildren. The B/Yamagata lineage might have become extinct in 2020/2021 due to
COVID-19 pandemic The COVID-19 pandemic, also known as the coronavirus pandemic, is an ongoing global pandemic of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The novel virus was first identi ...
measures.


Morphology

The Influenza B virus
capsid A capsid is the protein shell of a virus, enclosing its genetic material. It consists of several oligomeric (repeating) structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or ma ...
is enveloped while its
virion A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsky's ...
consists of an envelope, a matrix protein, a nucleoprotein complex, a
nucleocapsid A capsid is the protein shell of a virus, enclosing its genetic material. It consists of several oligomeric (repeating) structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may ...
, and a
polymerase A polymerase is an enzyme ( EC 2.7.7.6/7/19/48/49) that synthesizes long chains of polymers or nucleic acids. DNA polymerase and RNA polymerase are used to assemble DNA and RNA molecules, respectively, by copying a DNA template strand using ba ...
complex. It is sometimes spherical and sometimes filamentous. Its 500 or so surface projections are made of hemagglutinin and
neuraminidase Exo-α-sialidase (EC 3.2.1.18, sialidase, neuraminidase; systematic name acetylneuraminyl hydrolase) is a glycoside hydrolase that cleaves the glycosidic linkages of neuraminic acids: : Hydrolysis of α-(2→3)-, α-(2→6)-, α-(2→8)- glyc ...
.


Genome structure and genetics

The Influenza B virus
genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ...
is 14,548
nucleotide Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecu ...
s 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 An envelope is a common packaging item, usually made of thin, flat material. It is designed to contain a flat object, such as a letter or card. Traditional envelopes are made from sheets of paper cut to one of three shapes: a rhombus, a ...
. The subtypes of influenza A virus are estimated to have diverged 2,000 years ago. Influenza viruses A and B are estimated to have diverged from a single ancestor around 4,000 years ago, while the ancestor of influenza viruses A and B and the ancestor of influenza virus C are estimated to have diverged from a
common ancestor Common descent is a concept in evolutionary biology applicable when one species is the ancestor of two or more species later in time. All living beings are in fact descendants of a unique ancestor commonly referred to as the last universal comm ...
around 8,000 years ago.
Metatranscriptomics Metatranscriptomics is the science that studies gene expression of microbes within natural environments, i.e., the metatranscriptome. It also allows to obtain whole gene expression profiling of complex microbial communities. While metagenomics foc ...
studies have also identified closely related "Influenza B-like" viruses such as the Wuhan spiny eel influenza virus and also "Influenza-B like" viruses in a number of vertebrate species such as salamanders and fish.


Vaccine

In 1936, Thomas Francis Jr. discovered the ferret influenza B virus. Also in 1936, Macfarlane Burnet made the discovery that influenza virus may be cultured in hen embryonated eggs. This prompted research into the properties of the virus and the creation and application of inactivated vaccines in the late 1930s and early 1940s. Inactivated vaccines' usefulness as a preventative measure was proven in the 1950s. Later, 2003 saw the approval of the first live, attenuated influenza vaccine. Looking into influenza B specifically, Thomas Francis Jr. isolated influenza B virus in 1936. However, it was not until 1940 when influenza B viruses were discovered. In 1942, a new bivalent vaccine was developed that protected against both the H1N1 strain of influenza A and the newly discovered influenza B virus. In today’s current world, even while some technology has advanced and flu vaccines now cover both strains of influenza A and B, the science is still based on findings from almost a century ago. The viruses included in flu vaccines are changed each year to match the strains of flu that are most likely to make people sick that year since flu viruses can develop swiftly and new mutations have appeared each year, like H1N1. Even though there are two different lineages of influenza B viruses that circulate during most seasons, flu vaccinations were long meant to protect against three different flu viruses: the influenza A(H1N1), influenza A(H3N2), and one influenza B virus. The second lineage of the B virus was since added to provide greater defense against circulating flu viruses. Two influenza A viruses and two influenza B viruses are among the four flu viruses that a quadrivalent vaccine is intended to protect against. All flu vaccines in the United States today are quadrivalent. The four main types of Type A and B influenza viruses that are most likely to spread and make people sick during the upcoming flu season are the targets of seasonal influenza (flu) vaccines. All of the available flu vaccinations in the United States offer protection against the influenza A(H1), A(H3), B/Yamagata, and B/Victoria lineage viruses. Each of these four vaccine virus components is chosen based on the following criteria: which flu viruses are infecting people ahead of the upcoming flu season, how widely they are spreading, how well the vaccines from the previous flu season may protect against those flu viruses, and the vaccine viruses' capacity to offer cross-protection. For the 2022-2023 flu season, there are three flu vaccines that are preferentially recommended for people 65 years and older; various influenza (flu) vaccinations are authorized for use in people of various age groups. On March 3, 2022, the FDA's Vaccines and Related Biological Products Advisory Committee (VRBPAC) convened in Silver Spring, Maryland, to choose the influenza viruses that will make up the influenza vaccine for the 2022–2023 influenza season in the United States. The committee proposed using A(H1N1)pdm09, A(H3N2), and B/Austria/1359417/2021-like viruses for trivalent influenza vaccines to be utilized in the U.S. for the 2022–2023 influenza season.


Influenza B Throughout the Decades: Its Discovery and Development

In 1940, an acute respiratory illness outbreak in Northern America led to the discovery of influenza B virus (IBV), which was later discovered to not have any antigenic cross-reactivity with influenza A virus (IAV). Based on calculations of the rate of amino acid substitutions in HA proteins, it was estimated that IBV and IAV diverged from one another around 4000 years ago. However, the mechanisms of replication and transcription, as well as the functionality of the majority of viral proteins, appear to be largely conserved, with some unusual differences. Although IBV has occasionally been found in seals and pigs, its primary host species is the human. IBVs can also spread epidemics throughout the world, but they receive less attention than IAVs do due to their less prevalent nature, both in infecting hosts and in the symptoms that result from infection. IBVs used to be unclassified, but since the 1980s, they have been divided into the B/Yamagata and B/Victoria lineages. IBVs have further divisions known as clades and sub-clades, just like IAVs do. Hemagglutinin (HA) and neuraminidase (NA) are two virus surface antigens that are constantly changing. Antigenic drift or antigenic shift are two possible influenza viral changes. Small changes in the HA and NA of influenza viruses caused by antigenic drift result in the creation of novel strains that the immune system of humans might not be able to identify. These emerging strains are the influenza virus's evolutionary responses to a potent immunological response across the population. The main cause of influenza recurrence is antigenic drift, which makes it essential to reevaluate and update the influenza vaccine's ingredient list every year. Annual influenza outbreaks are caused by antigenic drift and declining immunity, when the residual defenses from prior exposures to related viruses are incomplete. Antigenic drift occurs in Influenza A, B, and C. Hemagglutination-inhibition experiments using ferret serum after infection allowed the identification of two very different antigenic influenza type B variants in the years 1988 – 1989. These viruses shared antigens with either B/Yamagata/16/88, a variation that was discovered in Japan in May 1988, or B/Victoria/2/87, the most recent reference strain. The B/Victoria/2/87 virus shared antigens with all influenza B viruses discovered in the United States during an outbreak in the winter of 1988 – 1989. In Japan, influenza B virus reinfection was investigated virologically in 1985 – 1991 and epidemiologically in 1979 – 1991 in children. Four influenza B virus outbreaks that each included antigenic drift occurred during the course of this study. Between the epidemics in 1987 – 1988 and 1989 – 1990, there was a significant genetic and antigenic change in the viruses. Depending on the influenza seasons, the minimum rate of reinfection with influenza B virus for the entire period was between 2 and 25%. Haemagglutination inhibition assays were used to examine the antigens of the influenza B virus primary and reinfection strains that were isolated from 18 children between the years of 1985 and 1990, which encompassed three epidemic periods. The findings revealed that reinfection occurred with the viruses recovered during the 1984 – 1985 and 1987 – 1988 influenza seasons, which belonged to the same lineage and were antigenically close. Today, reinfection continues as increased influenza activity was reported in the United States in November 2022 due to the winter weather.


References


External links


Influenza Research Database
Database of influenza genomic sequences and related information.

* {{Taxonbar, from=Q1089532, from2=Q51916573, from3=Q17330082 Orthomyxoviridae Influenza de:Influenzavirus#Influenza-B-Subtypen