Family: Nairoviridae

Genus: Orthonairovirus

Distinguishing features

The consensus terminal nucleotide sequences of the L, M, and S genome segments are typically characterized by a genus-specific 5′ genomic segment terminus 5′-UCUCAAAGA-3′ and 3′ genomic segment terminus of 5′-UCUUUGAGA-3′ ; however several members of the Orthonairovirus genus have termini that differ by one nucleotide. Glycoprotein (GP) subunits G_N and G_C and non-structural proteins are encoded as a precursor polyprotein by the M RNA. Genetic reassortment has been demonstrated between viruses belonging to the same species but not between members of different species. Of the 15 species within this genus, viruses of all but two species (Hughes orthonairovirus and Sakhalin orthonairovirus) have been detected in mammals. Of those members with known vectors, the majority of viruses within this genus are transmitted by ticks to mammalian hosts or birds. Some viruses are transmitted transovarially in arthropods. 

Virion

See discussion under family description. 

Genome organization and replication

The orthonairovirus genome consists of three single-stranded, negative-sense RNA molecules, termed S (small), M (medium), and L (large). These RNAs encode three different proteins: S RNA encodes N, the M RNA encodes the viral glycoprotein precursor (GPC), and the L RNA encodes the large protein (L) with its RNA-directed RNA polymerase (RdRP) domain in the virus-complementary sense RNA (Figure 1. Orthonairovirus). 

Figure 1. Orthonairovirus.  Schematic representation of orthonairovirus genome organization.

For further details see discussion under family description. 

Biology

See discussion under family description. 

Derivation of names

Orthonairovirus: from the Ancient Greek ὀρθός (orthós), meaning upright or straight and Nairobi, from Nairobi (Kenya) where Nairobi sheep disease virus was first isolated, and virus, suffix for a genus. 

Species demarcation criteria

Demarcation of genera is based upon considerations of phylogeny, significant differences in member virus genome architecture, virion antigenicity, and virus ecology (e.g., host range, pathobiology, and transmission patterns. 

Phylogenetic relationships

Phylogenetic relationships across the genus have been estimated using maximum likelihood trees generated from complete and partial protein sequences (Figure 4. Nairoviridae). 

Member Species

The Member Species table enumerating important virus exemplars classified under each species of the genus is provided at the bottom of the page.

Related, unclassified viruses

Virus names and virus abbreviations are not official ICTV designations. 

⁺Not currently released. The Meram sequence are available in the sequence alignments on the Resources page. 

*Coding region sequences incomplete.