Family: Nyamiviridae
Genus: Nyavirus
Distinguishing features
The genus Nyavirus includes six species. Based on the genomic structure and phylogeny, the members of these species, San Jacinto virus (SJCV), Sierra Nevada virus (SNVV), Sekira virus (SEKRV), Jeremy Point virus (JPV), Nyamanini virus (NYMV), and Midway virus (MIDWV) are closely related (Mihindukulasuriya et al., 2009, Rogers et al., 2014, Walker et al., 2019, Kobayashi et al., 2021). L protein amino acid sequence identities among these nyaviruses are 62.4–82.4%, while genome sequence identities range from 66.4–67.4%.
Virion
Morphology
Sierra Nevada virus particles are enveloped and spherical with a diameter of 100–130 nm (Figure 1.Nyamiviridae).San Jacinto virus-infected Vero E6 cells release large spherical (320–800 nm) or pleomorphic and elongated particles (350 × 540 nm to 280 ×1120 nm and 3280 × 1275 nm).
Nucleic acid
Non-segmented, negative-sense RNA.
Proteins
Nyavirus genomes encode up to six structural proteins. Among them, the nucleocapsid protein (N), glycoprotein (G), and large protein (L) are identified on the basis of sequence similarity and structural properties shared with mononegavirus homologues. The functions of the other encoded proteins are largely unknown but may be those of matrix and polymerase cofactor proteins (Mihindukulasuriya et al., 2009). SJCV has an additional unique small ORF P6 between the G and L ORFs. The SEKRV genome appears to have only 4 ORFs, lacking the M and G genes (Kobayashi et al., 2021) whereas the JPV genome contains 8 ORFs.
Genome organization and replication
Nyavirus negative-sense RNA genomes range from 11.6–13.3 kb (Figure 2.Nyamiviridae). Nyaviruses have non-segmented genomes with 4 to 8 ORFs that encode the structural proteins and putative accessory proteins (Mihindukulasuriya et al., 2009, Rogers et al., 2014, Kobayashi et al., 2021). Knowledge of nyavirus replication is limited. Nyamanini virus replicates in the nucleus of infected cells (Herrel et al., 2012).
Biology
Although NYMV and MIDWV have been isolated from birds of different species and their ticks, it is unclear whether SNVV can also infect birds. SJCV was isolated from the brains of dead birds.
Antigenicity
SNVV is antigenically distinct from MIDWV and NYMV when tested in complement fixation tests, whereas MIDWV and NYMV are serologically related (Mihindukulasuriya et al., 2009, Rogers et al., 2014).
Species demarcation criteria
Species are demarcated based upon their members’ phylogenetic relationships and host.