Family: Rhabdoviridae

Genus: Betanemrhavirus

Distinguishing features

Viruses assigned to the genus Betanemrhavirus form a distinct monophyletic group based on well-supported Maximum Likelihood or Maximum Clade Credibility trees inferred from complete L sequences. Members of the genus have been detected in roundworms (Nematoda). They are distant phylogenetically from nematode viruses assigned to the genus Alphanemrhavirus.

Virion

Morphology

Viruses assigned to the genus have not yet been visualized by electron microscopy.

Nucleic acid

Betanemrhavirus genomes consist of a single molecule of negative-sense, single-stranded RNA of approximately 13.3–13.8 kb (Shi et al., 2016).

Proteins

Betanemrhavirus N, P, M, G and L proteins share sequence homology and/or structural characteristics with the cognate proteins of other rhabdoviruses. Betanemrhavirus G proteins are class I transmembrane glycoproteins. Alignment with the G protein of vesicular stomatitis Indiana virus (VSIV; species Vesiculovirus indiana) indicates likely conservation of 10 of the 12 conserved cysteine residues that are typical of animal rhabdovirus G proteins (Walker and Kongsuwan 1999, Roche et al., 2006). Only disulphide bridge C_IX-C_XI does not appear to be conserved in the betanemrhaviruses. Conservation of eight additional cysteine residues in only the betanemrhavirus ectodomains suggests there may be four additional disulphide bridges that are not present in VSIV.

Genome organisation and replication

Betanemrhavirus genomes include the five genes (N, P, M, G and L) encoding the structural proteins and an additional orthologous gene (U1) between the P and M genes (Figure 1.Betanemrhavirus). In Hubei rhabdo-like virus 9, there is also a unique additional gene (U2) between the M and G genes.

Figure 1.Betanemrhavirus. Schematic representation of betanemrhavirus genomes shown in reverse (positive-sense) polarity. The five long open reading frames (ORFs) in the N, P, M, G and L genes are shown (open arrows). ORF U1 (orange) in each virus and ORF U2 (light blue) in Hubei rhabdo-like virus 9 are also shown.

Biology

Shayang ascaridia galli virus 2 (species Betanemrhavirus shayang) was detected in a pool of roundworms (Ascaridia galli and Ascaris suum) sampled in Hubei Province, China, in 2014 (Shi et al., 2016). Hubei rhabdo-like virus 9 (species Betanemrhavirus hubei) also was detected in a pool of large pig roundworms (A. suum) sampled in Hubei Province, China, in 2014 (Shi et al., 2016). No isolates are currently available for either of these viruses.

Species demarcation criteria

Viruses assigned to different species within the genus have several of the following characteristics: A) minimum amino acid sequence divergence of 10% in N proteins; B) minimum amino acid sequence divergence of 10% in the L proteins; C) minimum amino acid sequence divergence of 15% in G proteins; D) significant differences in genome organisation as evidenced by numbers and locations of ORFs; E) can be distinguished in virus neutralisation tests; and F) occupy different ecological niches as evidenced by differences in invertebrate hosts.