Family: Rhabdoviridae

Genus: Alphadrosrhavirus

Distinguishing features

Viruses assigned to the genus Alphadrosrhavirus 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 flies of various species (Drosophilidae). They are distant phylogenetically from rhabdoviruses of flies that have been assigned to the genus Sigmavirus.

Virion

Morphology

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

Nucleic acid

Alphadrosrhavirus genomes consist of a single molecule of negative-sense, single-stranded RNA of approximately 14.7–15.5 kb (Li et al., 2015).

Proteins

Alphadrosrhavirus N, P, M, G and L proteins share sequence homology and/or structural characteristics with the cognate proteins of other rhabdoviruses. Alphadrosrhavirus 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). Conservation of two additional cysteine residues in only the alphadrosrhavirus ectodomains suggests there may be an additional disulphide bridge that is not present in VSIV.

Genome organisation and replication

Alphadrosrhavirus genomes include the five genes (N, P, M, G and L) encoding the structural proteins (Figure 1 Alphadrosrhavirus). They also share the common characteristic of an additional gene between the G and L genes (U1 in Shayang fly virus 3 [SyFV3; species Alphadrosrhavirus shayang] and U2 in Wuhan house fly virus 2 [WhHFV2; species Alphadrosrhavirus hubei]) in which there are two overlapping ORFs. Each of these ORFs (U1a and U1b in SYFV3; U2a and U2b in WhHFV2) encodes a small hydrophobic protein with a strongly predicted transmembrane domain. In WhHFV2, there is also an additional gene (U1) between the P gene and M gene containing a single ORF. Small alternative or overlapping ORFs also occur in the P genes of each virus but it is not known if they are expressed.

Figure 1 Alphadrosrhavirus. Schematic representation of alphadrosrhavirus 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). Shayang fly virus 3 ORF U1a/U1b and Wuhan house fly virus 2 U2a/U2b (dark blue/yellow), encode orthologous sets of accessory proteins. ORF U1 in WhHFV2 (purple) encodes a unique protein. Small alternative reading frames in the P genes (light blue and mid blue) are also shown.

Biology

SyFV-3 was discovered in a pool of oriental latrine flies (Chrysomya megacephala) collected in Hubei Province, China, in 2012 (Li et al., 2015). WhHFV-2 was discovered by high throughput sequencing in a pool of houseflies (Musca domestica) collected in Hubei Province, China, in 2013 (Li et al., 2015). 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.

Biology

SyFV-3 was discovered in a pool of oriental latrine flies (Chrysomya megacephala) collected in Hubei Province, China, in 2012 (Li et al., 2015). WhHFV-2 was discovered by high throughput sequencing in a pool of houseflies (Musca domestica) collected in Hubei Province, China, in 2013 (Li et al., 2015). 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.

Related, unclassified viruses

Virus names and virus abbreviations are not official ICTV designations.

* Coding region sequence incomplete