Viruses assigned to the genus Scophrhavirus comprise one of the five genera of rhabdoviruses that infect finfish, the other genera being Perhabdovirus, Siniperhavirus, Sprivivirus and Novirhabdovirus. Viruses assigned to the genus Scophrhavirus form a distinct monophyletic group based on well-supported Maximum Likelihood or Maximum Clade Credibility trees inferred from complete L sequences. They are most closely related to perhabdoviruses, siniperhaviruses and cetarhaviruses (infecting cetaceans).
Scophthalmus maximus rhabdovirus (SMRV; species Scophrhavirus maximus) virions have bullet-shaped morphology and reported to measure 80–100 nm in length and 40–60 nm in diameter (Zhang et al., 2007).
N, P, M, G and L share significant sequence homology with the homologous proteins of other rhabdoviruses.
Genome organisation and replication
Scophrhavirus genomes include five genes in the order 3′-N-P-M-G-L-5′ encoding a nucleoprotein, polymerase-associated protein, matrix protein, glycoprotein and RNA-directed RNA polymerase, respectively (Figure 1.Scophrhavirus). The SMRV genome also features an alternative ORF in the P gene (Px) commencing upstream of the P ORF and encoding a putative basic protein of 14.1 kDa (Zhu et al., 2011). The SMRV genome contains a leader region of 66 nt preceding the transcription initiation of the N gene, and a trailer of 67 nt following the transcription termination of the L gene (Zhu et al., 2011). The transcriptional initiation and the termination/polyadenylation signals are conserved for all genes, 3′-UUGU and 3′-AUAC(U)7, respectively, but the non-transcribed intergenic regions are variable. There is inverse complementarity between the 3′-leader and 5′-trailer sequences.
|Figure 1.Scophrhavirus. Schematic representation of scophrhavirus genomes shown in reverse (positive-sense) polarity. N, P, M, G and L represent ORFs encoding the structural proteins. There is an alternative ORF (Px) in the SMRV P gene (grey).|
SMRV was isolated from marine turbot fish (Scophthalmus maximus) with signs of lethal haemorrhagic disease collected from Shandong Province, China (Zhang et al., 2007). The virus also causes a similar haemorrhagic disease and mortalities in experimentally infected freshwater grass carp (Ctenopharyngodon idella). Wuhan redfin culter dimarhabdovirus (species Scophrhavirus chanodychthys) was detected in redfin culter (Chanodichthys erythropterus) collected in Hubei Province, China (Shi et al., 2018).
Polyclonal mouse antiserum to SMRV cross-reacts in immunoblots with the N protein of spring viraemia of carp virus (genus Sprivvirus) (Zhang et al., 2007).
Species demarcation criteria
Viruses assigned to different species within the genus Scophrhavirus have several of the following characteristics: A) minimum amino acid sequence divergence of 10% in N proteins; B) minimum sequence divergence of 10% in the L proteins; C) minimum amino acid sequence divergence of 15% in G proteins; D) can be distinguished in virus neutralisation tests; and E) occupy different ecological niches as evidenced by differences in vertebrate hosts.