''Picobirnavirus'' is a genus of

double-stranded RNA viruses Double-stranded RNA viruses (dsRNA viruses) are a polyphyletic group of viruses that have double-stranded genomes made of ribonucleic acid. The double-stranded genome is used to transcribe a positive-strand RNA by the viral RNA-dependent RNA pol ...

. It is the only genus in the family ''Picobirnaviridae''. Although

amniotes Amniotes are a clade of tetrapod vertebrates that comprises sauropsids (including all reptiles and birds, and extinct parareptiles and non-avian dinosaurs) and synapsids (including pelycosaurs and therapsids such as mammals). They are distingu ...

, especially mammals, were thought to serve as hosts, it has been recently suggested that these viruses might infect bacteria and possibly some other invertebrates. There are three species in this genus. Associated symptoms include

gastroenteritis Gastroenteritis, also known as infectious diarrhea and gastro, is an inflammation of the gastrointestinal tract including the stomach and intestine. Symptoms may include diarrhea, vomiting, and abdominal pain. Fever, lack of energy, and dehydra ...

in animals and humans, though the disease association is unclear.

Etymology

Picobirnavirus is a small (''pico'',

Spanish Spanish might refer to: * Items from or related to Spain: **Spaniards are a nation and ethnic group indigenous to Spain **Spanish language, spoken in Spain and many Latin American countries **Spanish cuisine Other places * Spanish, Ontario, Cana ...

for ''small''), bisegmented (''bi'',

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

for ''two''), double-stranded RNA virus. Picobirnaviruses were initially considered to be birna-like viruses, and the name was derived from birnavirus (bisegmented RNA), but the virions are much smaller (diameter 35 nm vs. 65 nm). Picobirnaviruses were first detected in humans and black-footed pigmy rice rats in 1988.

Structure

Viruses in the genus are non-enveloped, with icosahedral geometries, and T=3 symmetry. The diameter is around 35–40 nm.

Genome

The

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 ge ...

is linear, bipartite, and composed of double-stranded

RNA Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...

. It includes a ''segment 1'' which is 2.2–2.7

kilobase A base pair (bp) is a fundamental unit of double-stranded nucleic acids consisting of two nucleobases bound to each other by hydrogen bonds. They form the building blocks of the DNA double helix and contribute to the folded structure of both DNA ...

s (kb) in length and a ''segment 2'' which is 1.2–1.9 kb in length. The genome codes for three to four proteins. The capsid protein gene is encoded by the second open reading frame of the larger genomic segment 1. Picobirnaviruses are divided into two genogroups on the basis of the sequence of ''segment 2''. The

RNA-dependent RNA polymerase RNA-dependent RNA polymerase (RdRp) or RNA replicase is an enzyme that catalyzes the replication of RNA from an RNA template. Specifically, it catalyzes synthesis of the RNA strand complementary to a given RNA template. This is in contrast to t ...

(RdRp) is encoded by ''segment 2''. The group viruses have been isolated from humans and other mammals, as well as birds and

squamates Squamata (, Latin ''squamatus'', 'scaly, having scales') is the largest order of reptiles, comprising lizards, snakes, and amphisbaenians (worm lizards), which are collectively known as squamates or scaled reptiles. With over 10,900 species, i ...

Life cycle

Picobirnaviruses target intestine tissue. Entry into the host cell is achieved by penetration into the host cell. Once in the host cell, viral replication is cytoplasmic. Replication follows the double-stranded RNA virus replication model. Double-stranded RNA virus transcription is the method of transcription. The viruses are released from the cell by budding. Mammals serve as the natural host. Transmission routes are fecal-oral.

Taxonomy

Picobirnaviruses were initially thought to belong to the family ''

Birnaviridae ''Birnaviridae'' is a family of double-stranded RNA viruses. Salmonid fish, birds and insects serve as natural hosts. There are currently 11 species in this family, divided among seven genera. Diseases associated with this family include infec ...

'', but later were confirmed to differ with respect to host, virion size, capsid, RNA-dependent RNA polymerase, genome size, and organization. The family ''Picobirnaviridae'' is now classified distinctly and composed of one genus ''Picobirnavirus'', which has three species: *'' Beihai picobirnavirus'' *'' Equine picobirnavirus'' *''Human picobirnavirus''

References

External links

* * *
Taxonomic proposal for picobirnaviridae at the ICTV

ICTV Report: ''Picobirnaviridae''
{{Taxonbar, from=Q7191036 Double-stranded RNA viruses Riboviria Virus genera