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

Structure

The

virions A virion (plural, ''viria'' or ''virions'') is an inert virus particle capable of invading a cell. Upon entering the cell, the virion disassembles and the genetic material from the virus takes control of the cell infrastructure, thus enabling th ...

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, having 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.

Genome

Nairovirus genomes are negative sense, single-stranded RNA. The complete

genome A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as ...

is about 17,100–22,800

nucleotide Nucleotides are Organic compound, organic molecules composed of a nitrogenous base, a pentose sugar and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both o ...

s 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

glycoprotein Glycoproteins are proteins which contain oligosaccharide (sugar) chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known a ...

s 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 A capsid is the protein shell of a virus, enclosing its genetic material. It consists of several oligomeric (repeating) structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or ma ...

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 In molecular biology, circular ribonucleic acid (or circRNA) is a type of single-stranded RNA which, unlike linear RNA, forms a covalently closed continuous loop. In circular RNA, the 3' and 5' ends normally present in an RNA molecule have been ...

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

Replication

Nairoviruses attach to the host receptor 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 The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...

, commencing transcription. Transcription and replication occur within the cell, and the newly synthesized virions are released by

budding Budding or blastogenesis is a type of asexual reproduction in which a new organism develops from an outgrowth or bud due to cell division at one particular site. For example, the small bulb-like projection coming out from the yeast cell is kno ...

Transmission and distribution

Members of this viral genus infect many different

vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

hosts, and are transmitted via ticks. Members of the genus ''Nairovirus'' may be found the world over, wherever their

arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

vectors and vertebrate hosts are found together.

Taxonomy

The genus contains the following species, listed by scientific name and followed by the exemplar virus of the species: * ''Orthonairovirus abuhammadense'', Abū Ḥammād virus * ''Orthonairovirus abuminaense'', Abū Mīnā virus * ''Orthonairovirus amblyommae'', Kupe virus * ''Orthonairovirus antuense'', Antú virus * ''Orthonairovirus artashatense'', Artashat virus * ''Orthonairovirus australiaense'', Vinegar Hill virus * ''Orthonairovirus avalonense'', Avalon virus * ''Orthonairovirus bandiaense'', Bandia virus * ''Orthonairovirus buranaense'', Burana virus * ''Orthonairovirus bushkeyense'', Farallon virus * ''Orthonairovirus chimense'', Chim virus * ''Orthonairovirus clomorense'', Clo Mor virus * ''Orthonairovirus crocidurae'', Wufeng Crocidura attenuata orthonairovirus 1 * ''Orthonairovirus dermacentoris'', Pacific Coast tick nairovirus * ''Orthonairovirus dugbeense'', Dugbe virus * ''Orthonairovirus erveense'', Erve virus * ''Orthonairovirus esteroense'', Estero Real virus * ''Orthonairovirus gossasense'', Gossas virus * ''Orthonairovirus gubboense'', Gubbo nairovirus * ''Orthonairovirus haemorrhagiae'', Crimean-Congo hemorrhagic fever virus * ''Orthonairovirus hazaraense'',

Hazara virus In 1954 the Hazara virus, one of the 34 tick-borne viruses of the genus '' Orthonairovirus'', was discovered in Pakistan in the ''Ixodes'' tick native to that region. Today this virus is studied in mice in an attempt to develop treatments for the ...

* ''Orthonairovirus huangpiense'', Huángpí tick virus 1 * ''Orthonairovirus issykkulense'', Issyk-kul virus * ''Orthonairovirus japonicum'', Tofla virus * ''Orthonairovirus kasokeroense'', Kasokero virus * ''Orthonairovirus keterehense'', Keterah virus * ''Orthonairovirus khani'', Dera Ghazi Khan virus * ''Orthonairovirus lambarenense'', Lamusara virus * ''Orthonairovirus lusakaense'', Leopards Hill virus * ''Orthonairovirus macquariense'', Taggert virus * ''Orthonairovirus manidae'', Pangolin orthonairovirus * ''Orthonairovirus meihuashanense'', Méihua Mountain virus * ''Orthonairovirus meramense'', Meram virus * ''Orthonairovirus nairobiense'', Nairobi sheep disease virus * ''Orthonairovirus parahaemorrhagiae'', Aigai virus * ''Orthonairovirus peruense'', Punta Salinas virus * ''Orthonairovirus qalyubense'', Qalyub virus * ''Orthonairovirus randallense'', Sapphire II virus * ''Orthonairovirus sakhalinense'', Sakhalin virus * ''Orthonairovirus sinense'', Orthonairovirus sp. strain YS * ''Orthonairovirus soldadoense'', Soldado virus * ''Orthonairovirus songlingense'', Sōnglǐng virus * ''Orthonairovirus sulinaense'', Sulina virus * ''Orthonairovirus sunci'', Cencurut virus * ''Orthonairovirus tachengense'', Tǎchéng tick virus 1 * ''Orthonairovirus thiaforaense'', Thiafora virus * ''Orthonairovirus tomdiense'', Tamdy virus * ''Orthonairovirus tunisense'', Tunis virus * ''Orthonairovirus wenzhouense'', Wēnzhōu tick virus * ''Orthonairovirus yezoense'', Yezo virus * ''Orthonairovirus yogueense'', Yogue virus * ''Orthonairovirus zirkuense'', Zirqa virus

Clinical importance

Members of this viral genus which infect humans include 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. Kasokero virus and Erve virus are likely also pathogenic for humans.

Evolution

Phylogenetic analysis has shown that these viruses fall into two major monophyletic groups, the hard (''

Ixodidae The Ixodidae are the family of hard ticks or scale ticks, one of the three families of ticks, consisting of 771 species, . They are known as 'hard ticks' because they have a scutum or hard shield, which the other major family of ticks, the 'sof ...

'') and soft (''

Argasidae The Argasidae are the family of soft ticks, one of the three families of ticks. The family contains 193 species, although the composition of the genera is less certain, and more study is needed before the genera can become stable. The currently a ...

'') 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. Additionally, nairoviruses vectored by ticks of the genera '' Argas'', ''Carios'' and ''

Ornithodoros ''Ornithodoros'' is a genus in the soft-bodied tick family, Argasidae. It is distinguished from other genera in the family by the absence of a lateral 'suture' line. It is the largest genus within Argasidae, consisting of approximately 130 specie ...

'' 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.

References

External links

ICTV Report: ''Nairoviridae''

{{Taxonbar, from=Q29001085 Nairoviridae Virus genera