Family: Rhabdoviridae

Genus: Alphaplatrhavirus

Distinguishing features

Viruses assigned to the genus Alphaplatrhavirus 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 flatworms (phylum Platyhelminthes), fecal samples or vertebrate visceral tissue samples. They are distinct phylogenetically from rhabdoviruses assigned to the genera Betaplatrhavirus and Gammaplatrhavirus..

Virion

Morphology

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

Nucleic acid

Alphaplatrhavirus genomes consist of a single molecule of negative-sense, single-stranded RNA and range from approximately 11.4–15.6 kb (Bodewes et al., 2014, Shi et al., 2018, Dheilly et al., 2022, Chen et al., 2023).

Proteins

Alphaplatrhavirus N, P, M, G and L proteins appear to be homologous with corresponding proteins of other rhabdoviruses. Alphaplartrhavirus G proteins are class I transmembrane glycoproteins. Alignment of platrhavirus G proteins with that of vesicular stomatitis Indiana virus (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), and 4–6 additional conserved cysteine residues that are likely to form 2–3 more disulphide bridges in the folded protein. Alphaplatrhaviruses usually encode one or more additional proteins, one of which may have the structural characteristucs of a class I viroporin.

Genome organisation and replication

Alphaplatrhavirus genomes include the five genes (N, P, M, G and L) encoding the structural proteins and there is usually at least one additional gene between the G and L genes (Figure 1 Alphaplatrhavirus). Alternative long ORFs may occur in N, P, M, or one of the additional genes between G and L, but it is not known if they are expressed in infected cells (Figure 1 Alphaplatrhavirus).

Figure 1 Alphaplatrhavirus. Schematic representation of alphaplatrhavirus genomes 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). Additional and alternative ORFs are shown in grey with those encoding predicted class I viroporins shown in yellow.

Biology

Alphaplatrhaviruses have been detected by metagenomic sequencing of platyhelminths that parasitise invertebrate and vertebrate hosts (Dheilly et al., 2022). These include cestode worms (Triaenophorus nodulosus and Schistocephalus solidus) and trematode worms (Microphallus sp.2 LB-2020, Sphaeridiotrema pseudoglobulus, Schistosoma turkestanicum, Metorchis orientalis and Dicrocoelium dendriticum). Fox fecal rhabdovirus (species Platrhavirus vulpes) was detected by metagenomic sequencing of feces from a fox (Vulpes vulpes) collected in Spain (Bodewes et al., 2014). Other alphaplatrhaviruses have been detected by metatranscriptomic sequencing of various visceral organs of bats, shrews and fish (Shi et al., 2018, Chen et al., 2023). No isolates are currently available for any of these viruses. Available evidence suggests that those alphaplatrhaviruses detected in vertebrates are likely due to platyhelminth infestation.

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 arthropod and/ or vertebrate hosts.