Orthobunyavirus


Orthobunyavirus is a genus of the Peribunyaviridae family in the order Bunyavirales. There are currently ~170 viruses recognised in this genus. These have been assembled into 88 species and 20 serogroups.
The name Orthobunyavirus derives from Bunyamwera, Uganda, where the original type species Bunyamwera orthobunyavirus was first discovered, along with the prefix orthos meaning 'straight.'
The type species is Bunyamwera orthobunyavirus.

Epidemiology

The genus is most diverse in Africa, Australia and Oceania, but occurs almost worldwide. Most orthobunyavirus species are transmitted by gnats and cause diseases of cattle. The California encephalitis virus, the La Crosse virus and the Jamestown Canyon virus are North American species that cause encephalitis in humans.

Virology

Vectors

The primary vectors of Orthobunyaviruses are hematophagous insects of the Culicidae family, including members from a number of mosquito genera and biting midges. Although transmission by ticks and bed bugs may also occur. Viral vector preference is generally strict, with only a one or very small number of vectors transmitting a specific virus in the region, even where multiple viruses and vectors overlap. Organisms related to the preferential vector may be able to carry a virus but not competently transmit it.
The vector arthropod acquires the virus while taking a blood meal from an infected host. In mosquitoes, replication of orthobunyaviruses is enhanced by immune modulation that occurs as a result of blood protein digestion producing GABA and the activation of GABAergic signalling. Infection is transmitted to a new host via viral particles in vector saliva. Orthobunyavirus infection in arthropod cells is not fully understood, but is generally non-cytopathological and deleterious effects are minimal. Infected mosquitoes may experience an increase in fitness. Transorvarial transmission has been observed among mosquitoes infected with orthobunyaviruses of the California serogroup Like mosquitoes, only female culicoid midges feed on blood; they prefer indoor feeding particularly during rain.

Sylvatic Cycle Hosts

In the slyvatic cycle, viruses are transmitted between mammalian hosts by the arthropod vector. A diverse range of mammals have been identified or implicated as hosts or reservoirs of orthobunyaviruses including: non-human primates, sloths, wild and domestic birds, marmosets, rodents, and large mammals such as deer, moose, and elk.

Infection

Infection begins with the bite of an infected competent vector organism. Viral entry proceeds by receptor-mediated endocytosis, but which receptors unknown. Although, Heparan sulfate and DC-SIGN have been identified as viral entry components in some orthobunyaviruses. Gn/Gc heterodimers on the viral surface are responsible for target cell recognition, with Gc is considered the primary attachment protein, although Gn has been suggested as the attachment protein for LACV in arthropod cells. Acidification of the endosome triggers a conformational change in the Gc fusion peptide, uncoating the ribonuclearprotein as it is released into the cytoplasm.
Upon release into the cytoplasm, primary transcription begins with an endonuclease domain on L protein engaging in a process known as "cap-snatching." During cap-snatching, 10-18 nucleotides of 5' 7-methylguanylate primers are cleaved from host mRNAs and attached to prime the 5' end of the viral RNAs. Like all negative-sense RNA viruses, orthobunyaviruses require ongoing, concurrent translation by the host cell to produce full-length viral mRNAs, consequently the 3' end of orthobunyavirus mRNAs lack polyadenylation. Notably they are also missing the signal for polyadenylation; instead the 3' ends are thought to form a stem-loop structure. Antigenomes used as templates for replication of the viral genome are produced by L protein RdRp without the need for primers. Both negative-sense genomes and positive-sense antigenomes are associated with N proteins at all times during the replication cycle. Thus, N and L are the minimum proteins required for transcription and replication
The M genome segment codes for the Gn-NSm-Gc polyprotein on a single open-reading frame which is cotranslationally cleaved by internal signal peptides and host signal peptidase. The free glycoproteins Gc and Gn insert into the membrane of the endoplasmic reticulum and form heterodimers. A Golgi retention signal on Gn, permits transport of the heterodimers to the Golgi apparatus, where glycosylation occurs. The presence of the viral glycoproteins modifies the Golgi membrane to enable budding of RNPs into a Golgi derived tubular viral factory. As segmented viruses, orthobuynaviruses require precise packaging of one of each of the three genomic segments into the final virion to produce a mature, infectious particle. Packaging appears to be directed by signals contained entirely within UTR sequences. The packaged genomes acquire a lipid membrane as they bud into the viral factories, are then transported to the host cell plasma membrane and released via exocytosis. A final gylcoprotein modification upon release produces a mature, infectious particle.

Evolution

Orthobunyaviruses evolve partly by a key mechanism known as genomic reassortment, which also occurs in other segmented viruses. When viruses of the same group co-infect a host cell, mixtures and novel combinations of the S, M, and L segments can be produced, increasing diversity. The most common reassortment events are with the L and S segments.

Serogroups

The taxonomy remains somewhat fluid as relatively few viral genomes in this genus have been sequenced. Several of the viruses listed have been shown to be recombinants of other viruses and may be reclassified.
18 serogroups have been recognized on the basis of the results of cross-hemagglutination inhibition and antibody neutralization relationships. Another - Wyeomyia - has since been recognised. Several viruses have not yet been classified into one of the serogroups.
The Simbu serogroup is the largest and contains at least 25 members. There are at least 13 members in the Group C serogroup.
Medically important viruses belong to the Bwamba, Bunyamwera, California, Group C and Simbu serogroups.

Anopheles A serogroup



Chatanga virus

Inkoo virus

Jamestown Canyon virus

Jerry Slough virus

Keystone virus

Khatanga virus

La Crosse virus

Lumbo virus

Melao virus

Morro Bay virus

San Angelo virus

Serra do Navio virus

Snowshoe hare virus

South River virus

Tahyna virus

Trivittatus virus

Capim serogroup



Benevides virus

Capim virus

Gamboa serogroup

Bruconha virus

Ossa virus
Caraparu complex
Madrid complex
Oriboca complex
Ananindeua virus

Bertioga virus

Bimiti virus

Cananeia virus

Catu virus

Gan Gan virus

Guama virus

Guaratuba virus

Itimirim virus

Mahogany hammock virus

Mirim virus

Timboteua virus

Trubanaman virus

Koongol serogroup

Koongol virus

Wongal virus

Mapputta serogroup

Buffalo Creek virus

Mapputta virus

Maprik virus

Murrumbidgee virus

Salt Ash virus

Minatitlan serogroup

Minatitlan virus

Palestina virus

Nyando serogroup

Eretmapodites virus

Nyamdo virus

Olifanstlei serogroup

Botambi virus

Olifanstlei virus

Patois serogroup



Babahoyo virus

Pahayokee virus

Patois virus

Shark River virus

Zegla virus

Simbu serogroup

Iquitos virus

Jatobal virus

Leanyer virus

Mermet virus

Oya virus

Thimiri virus
Akabane serocomplex
Oropouche serocomplex
Sathuperi serocomplex
Shamonda serocomplex
Shuni serocomplex
Simbu complex
Bahig virus

Batama virus

Matruh virus

Tete virus

Tsuruse virus

Weldona virus

Turlock serogroup

Kedah virus

Lednice virus

M'Poko virus

Turlock virus

Umbre virus

Wyeomyia serogroup



Cachoeira Porteira virus

Iaco virus

Macaua virus

Sororoca virus

Taiassui virus

Tucunduba virus

Wyeomyia virus

Unclassified

Batama virus

Bellavista virus

Belmont virus

Enseada virus

Estero Real virus

Herbert virus

Jonchet virus

Jurona virus

Kaeng Khei virus

Kibale virus

Kowanyama virus

Mojuí dos Campos virus

Ntwetwe virus

Taï virus

Tataguine virus

Triniti virus

Witwatersrand virus

Wolkberg virus

Yacaaba virus