Nairovirus

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Nairovirus
Virus classification
Group: Group V ((-)ssRNA)
Order: Unassigned
Family: Bunyaviridae
Genus: Nairovirus
Type species
Dugbe virus
Species

Abu Hammad virus
Abu Mina virus
Artashat virus
Avalon virus
Bandia virus
Burana virus
Caspiy virus
Chim virus
Clo Mor virus
Crimean-Congo hemorrhagic fever virus
Dera Ghazi Khan virus
Dugbe virus
Erve virus
Farallon virus
Ganjam virus
Geran virus
Gossas virus
Hazara virus
Hughes virus
Issyk-Kul virus
Kasokero virus
Keterah virus
Kupe virus
Leopards Hill virus
Nairobi sheep disease virus
Paramushir virus
Puffin Island virus
Punte Salinas virus
Qalyub virus
Raza virus
Sakhalin virus
Soldado virus
Tamdy virus
Thiafora virus
Tillamok virus
Tofla virus
Yogue virus
Zirqa 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[edit]

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[edit]

The genus is divided into a number (at least nine) serogroups. The Hughes and Sakhalin serogroups appear to be sister groups.

Serogroups[edit]

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:

Abu Hammad virus
Abu Mina virus

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[edit]

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[edit]

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[edit]

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[edit]

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[edit]

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[edit]

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[edit]

  1. ^ a b c d 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.
  2. ^ Clerx, John PM, Jordi Casals, and David HL Bishop. "Structural Characteristics of Nairoviruses (Genus Nairovirus, Bunyaviridae)." Journal of General Virology 55 (1981): 165–78.
  3. ^ a b c d e f g h i 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>.
  4. ^ a b c d e f g "Nairovirus." Nairovirus. Viral Zone. <http://www.expasy.ch/viralzone/all_by_species/251.html>.
  5. ^ 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

External links[edit]