Nairovirus
| Nairovirus | |
|---|---|
| Virus classification | |
| Group: | Group V ((-)ssRNA) |
| Order: | Unassigned |
| Family: | Bunyaviridae |
| Genus: | Nairovirus |
| Type species | |
| Dugbe virus | |
| Species | |
|
Abu Hammad virus | |
Nairovirus is a genus in the family Bunyaviridae that include viruses with circular, negative-sense single stranded RNA. It got its name from the Nairobi sheep disease that affects the gastrointestinal tracts of sheep and goats. Viruses in this genus are tick-borne viruses that can have human or animal hosts.[1]
Taxonomy
The Nairobi sheep disease virus (NSD) is the prototype virus of the genus.[1][2]
This virus is found in East and Central Africa and causes acute hemorrhagic gastroenteritis in sheep and goats.
All virus in this genus are tick borne.
Serogroups
The genus is divided into a number (at least nine) serogroups. The Hughes and Sakhalin serogroups appear to be sister groups.
Serogroups
Crimean-Congo hemorrhagic fever
Dera Ghazi Khan
Hughes
Kasokero
Nairobi sheep disease
Qalyub
Sakhalin
Tamdy
Thiafora
Within each serogroup are a number of related viruses:
Crimean-Congo hemorrhagic fever serogroup:
- Crimean-Congo hemorrhagic fever virus
- Hazara virus
- Tofla virus
Dera Ghazi Khan serogroup:
Hughes serogroup:
- Farallon virus
- Hughes virus
- Puffin Island virus
- Punte Salinas virus
- Raza virus
- Soldado virus
- Zirqa virus
Kasokero serogroup
- Kasokero virus
- Yogue virus
Nairobi sheep disease serogroup:
- Dugbe virus
- Ganjam virus
- Kupe virus
- Nairobi sheep disease virus
Qalyub serogroup:
- Bandia virus
- Chim virus
- Geran virus
- Qalyub virus
Sakhalin serogroup:
- Avalon virus
- Paramushir virus
- Sakhalin virus
- Tillamok virus
Tamdy serogroup
- Burana virus
- Tamdy virus
Thiafora serogroup:
- Erve virus
- Thiafora virus
Genome
Nairovirus genomes are negative sense, single-stranded RNA. The complete genome is about 17,100–22,800 nucleotides long and is divided into three segments: large, medium, and small.[1] The large segment is about 11000–14400 nucleotides long (11–14.4 kb) and it encodes the viral polymerase.[3][4] The medium segment is about 4,400–6,300 nucleotides long (4.4–6.3 kb) and it encodes for glycoproteins G¬n and Gc.[3][4] The small segment is about 1,700–2,100 nucleotides long (1.7–2.1 kb) and it encodes the nucleocapsid protein.[1][3][4]
The genome has terminally redundant sequences with the sequences being repeated at both ends. The terminal nucleotides are base-paired forming non-covalently closed, circular RNA.[3] Both the 5’ and 3’ end have conserved regions of 9 nucleotides in length. The sequences are 5’end UCUCAAAGA and 3’end AGAGUUUCU.[3]
Virion
The virions for viruses in this genus have a spherical shape.[4] They range in size from about 80–120 nm in diameter with 50% of their weight attributed to proteins and 20–30% of their weight attributed to lipids.[3] The ribonucleocapsid is filamentous and has a length of about 200-300 nm and a width of about 2–2.5 nm.[3]
These nucleocapsids are surrounded by a single envelope that has projections made of glycoproteins protruding from its surface. These projections evenly cover the surface of the virion and are about 5–10 nm long.[3] They aid in attachment to the host receptor in replication.
Replication
Nairoviruses attach to the host receptors by their Gn-Gc glycoprotein dimer.[4] The virus is then endocytosed into the host cell via a vesicle. The ribonucleocapsid segments are released into the cytoplasm commencing transcription.[4] Transcription and replication occur in the cell and the newly synthesized virions are released by budding.
Transmission & Distribution
This virus infects many different vertebrate hosts and is transmitted via insects such as ticks and flies.[3]
There are no geographical localizations of this virus. It is widespread. However, the Crimean-Congo hemorrhagic fever virus is localized to Africa, Asia and Europe.[4]
Evolution
Phylogenetic analysis has shown that these viruses fall into two major monophyletic groups the hard (Ixodidae) and soft (Argasidae) tick vectored groups.[5] Fossil and phylogenetic data places the hard tick-soft tick divergence between 120 million years ago and 92 million years ago. This suggests that the Nairoviruses have been associated with these ticks for over 100 million years.
Additionally viruses vectored by ticks of the genera Argas, Carios and Ornithodoros form three separate monophyletic lineages again supporting the suggestion of host-virus cospeciation.
The hard bodied tick serogroups are
- Crimean-Congo hemorrhagic fever
- Nairobi sheep disease
- Sakhalin
- Tamdy
The soft bodied tick serogroups are
- Hughes
- Dera Ghazi Khan
- Qalyub
The vectors for the Kasokero and Thiafora serogroups are not currently known.
Clinical importance
Only three viruses in this genus to date have been recognised as human pathogens:
- Crimean-Congo hemorrhagic fever virus
- Dugbe virus
- Nairobi sheep disease virus.
A fourth— Erve virus —may also be pathogenic for humans.
Another - Kasokero virus - can infect humans.
Notes and references
- 1 2 3 4 Crabtree, Mary B., Rosemary Sang, and Barry R. Miller. "Kupe Virus, a New Virus in the Family Bunyaviridae, Genus Nairovirus, Kenya." Emerging Infectious Diseases 15 (2009): 147–54.
- ↑ Clerx, John PM, Jordi Casals, and David HL Bishop. "Structural Characteristics of Nairoviruses (Genus Nairovirus, Bunyaviridae)." Journal of General Virology 55 (1981): 165–78.
- 1 2 3 4 5 6 7 8 9 Büchen-Osmond, Cornelia. "00.011.0.03. Nairovirus." ICTVdb Virus Descriptions. 25 Apr. 2006. International Committee on Taxonomy of Viruses. 17 Apr. 2009 <http://phene.cpmc.columbia.edu/ICTVdB/00.011.0.03.htm>.
- 1 2 3 4 5 6 7 "Nairovirus." Nairovirus. Viral Zone. <http://www.expasy.ch/viralzone/all_by_species/251.html>.
- ↑ Honig JE, Osborne JC, Nichol ST (2004) The high genetic variation of viruses of the genus Nairovirus reflects the diversity of their predominant tick hosts. Virology 318(1):10-16