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Orthonairovirus

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Orthonairovirus
Crimean-Congo hemorrhagic fever virus virion and genome
Virus classification Edit this classification
(unranked): Virus
Realm: Riboviria
Kingdom: Orthornavirae
Phylum: Negarnaviricota
Class: Bunyaviricetes
Order: Hareavirales
Family: Nairoviridae
Genus: Orthonairovirus

Orthonairovirus is a genus of viruses in the family Nairoviridae of the order Hareavirales which includes viruses with circular, negative-sense single stranded RNA.[1] The name is derived from the Nairobi sheep disease which affects the gastrointestinal tracts of sheep and goats.[1] All viruses in this genus are tick-borne viruses with human or other vertebrate hosts.[2]

Structure

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The virions for viruses in this genus have a spherical shape.[3] 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.[1] The ribonucleocapsid is filamentous, having a length of about 200-300 nm and a width of about 2–2.5 nm.[1] 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.[1] They aid in attachment to the host receptor in replication.

Genome

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Crimean-Congo hemorrhagic fever 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.[2] The large segment is about 11000–14400 nucleotides long (11–14.4 kb), and it encodes the viral polymerase.[1][3] 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.[1][3] The small segment is about 1,700–2,100 nucleotides long (1.7–2.1 kb), and it encodes the nucleocapsid protein.[2]<[1][3]

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.[1] Both the 5’ and 3’ ends have conserved regions, 9 nucleotides in length. The sequences are, 5’end: UCUCAAAGA, and 3’end: AGAGUUUCU.[1]

Replication

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Nairovirus life cycle

Nairoviruses attach to the host receptor by their Gn-Gc glycoprotein dimer.[3] The virus is then endocytosed into the host cell via a vesicle. The ribonucleocapsid segments are released into the cytoplasm, commencing transcription.[3] Transcription and replication occur within the cell, and the newly synthesized virions are released by budding.

Transmission and distribution

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Members of this viral genus infect many different vertebrate hosts, and are transmitted via ticks.[1]

Members of the genus Nairovirus may be found the world over, wherever their arthropod vectors and vertebrate hosts are found together.[3]

Taxonomy

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The genus contains the following species, listed by scientific name and followed by the exemplar virus of the species:[4][5]

Clinical importance

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Members of this viral genus which infect humans include[6] Crimean–Congo hemorrhagic fever, Dugbe virus, Nairobi sheep disease virus, Songling virus, Yezo virus, Tacheng tick virus, Beiji orthonairovirus and Wetland virus. Except for the first they cause relatively mild disease.[6]

Kasokero virus[7] and Erve virus are likely also pathogenic for humans.[8]

Evolution

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Phylogenetic analysis has shown that these viruses fall into two major monophyletic groups, the hard (Ixodidae) and soft (Argasidae) tick-vectored groups.[9] 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, nairoviruses 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 tick vectors for the Kasokero and Thiafora serogroups are not currently known.

See also

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References

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  1. ^ a b c d e f g h i j k Kuhn JH, Alkhovsky SV, Avšič-Županc T, Bergeron É, Burt F, Ergünay K, et al. (April 2024). "ICTV Virus Taxonomy Profile: Nairoviridae 2024". The Journal of General Virology. 105 (4). doi:10.1099/jgv.0.001974. PMC 11094370. PMID 38687001.
  2. ^ a b c Crabtree MB, Sang R, Miller BR (February 2009). "Kupe virus, a new virus in the family bunyaviridae, genus nairovirus, kenya". Emerging Infectious Diseases. 15 (2): 147–154. doi:10.3201/eid1502.080851. PMC 2657624. PMID 19193256.
  3. ^ a b c d e f g "Nairovirus". Viral Zone. Swiss-Prot group of the SIB Swiss Institute of Bioinformatics.
  4. ^ "Virus Taxonomy: 2024 Release". International Committee on Taxonomy of Viruses. Retrieved 18 March 2025.
  5. ^ "Species List: Nairoviridae". International Committee on Taxonomy of Viruses. Retrieved 18 March 2025.
  6. ^ a b Zhang XA, Ma YD, Zhang YF, Hu ZY, Zhang JT, Han S, et al. (September 2024). "A New Orthonairovirus Associated with Human Febrile Illness". The New England Journal of Medicine. 391 (9): 821–831. doi:10.1056/NEJMoa2313722. PMID 39231344.
  7. ^ Schuh AJ, Amman BR, Patel K, Sealy TK, Swanepoel R, Towner JS (December 2020). "Human-Pathogenic Kasokero Virus in Field-Collected Ticks". Emerging Infectious Diseases. 26 (12): 2944–2950. doi:10.3201/eid2612.202411. PMC 7706932. PMID 33219649.
  8. ^ Ma J, Lv XL, Zhang X, Han SZ, Wang ZD, Li L, et al. (March 2021). "Identification of a new orthonairovirus associated with human febrile illness in China". Nature Medicine. 27 (3): 434–439. doi:10.1038/s41591-020-01228-y. PMID 33603240.
  9. ^ Honig JE, Osborne JC, Nichol ST (January 2004). "The high genetic variation of viruses of the genus Nairovirus reflects the diversity of their predominant tick hosts". Virology. 318 (1): 10–16. doi:10.1016/j.virol.2003.09.021. PMID 14972529.
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