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.
All virus in this genus are tick borne.
The genus is divided into a number (at least nine) serogroups. The Hughes and Sakhalin serogroups appear to be sister groups.
Crimean-Congo hemorrhagic fever
Dera Ghazi Khan
Nairobi sheep disease
Within each serogroup are a number of related viruses:
Crimean-Congo hemorrhagic fever serogroup:
Dera Ghazi Khan serogroup:
- Farallon virus
- Hughes virus
- Puffin Island virus
- Punte Salinas virus
- Raza virus
- Soldado virus
- Zirqa virus
Nairobi sheep disease serogroup:
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. The large segment is about 11000–14400 nucleotides long (11–14.4 kb) and it encodes the viral polymerase. 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. The small segment is about 1,700–2,100 nucleotides long (1.7–2.1 kb) and it encodes the nucleocapsid protein.
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. Both the 5’ and 3’ end have conserved regions of 9 nucleotides in length. The sequences are 5’end UCUCAAAGA and 3’end AGAGUUUCU.
The virions for viruses in this genus have a spherical shape. 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. The ribonucleocapsid is filamentous and has a length of about 200-300 nm and a width of about 2–2.5 nm.
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. They aid in attachment to the host receptor in replication.
Nairoviruses attach to the host receptors by their Gn-Gc glycoprotein dimer. The virus is then endocytosed into the host cell via a vesicle. The ribonucleocapsid segments are released into the cytoplasm commencing transcription. Transcription and replication occur in the cell and the newly synthesized virions are released by budding.
Transmission & Distribution
Phylogenetic analysis has shown that these viruses fall into two major monophyletic groups the hard (Ixodidae) and soft (Argasidae) tick vectored groups. Fossil and phylogenetic data places the hard tick-soft tick divergence between and . This suggests that the Nairoviruses have been associated with these ticks for over 100 million years.
The hard bodied tick serogroups are
- Crimean-Congo hemorrhagic fever
- Nairobi sheep disease
The soft bodied tick serogroups are
- Dera Ghazi Khan
The vectors for the Kasokero and Thiafora serogroups are not currently known.
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
- 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.
- 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>.
- "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