Genomic and molecular epidemiological characterization of a novel piscine poxvirus in the red seabream, Pagrus major

Abstract

Since 2020, unexplained mortality has been recorded in a red seabream hatchery. Affected juveniles exhibit skin darkening and sleep-like symptoms, which occasionally cause mass mortality. In this study, we detected a novel poxvirus genome in diseased fish via next-generation sequencing. Transcriptome analysis of moribund individuals revealed multiple contigs with sequence homology to the salmon gill poxvirus, suggesting the presence of a related viral agent. Subsequent metagenomic analysis led to the assembly of a 308-kbp viral genome of a novel piscine poxvirus, designated Japanese seabream poxvirus (JSPV), containing 338 predicted open reading frames. DNA polymerase of JSPV shared 62 and 44 % amino acid identity with those of the salmon gill poxvirus and carp edema virus, respectively. Comparative genomic analysis of piscine poxviruses revealed that genome synteny was highly conserved in the central region. Subsequently, a PCR method was developed and I7L, which encodes the virion core cysteine protease, was successfully detected in all JSPV genogroups. Based on the partial sequence of I7L, JSPV was classified into two major genogroups: I and II. Genogroup I was further subdivided into genogroups Ia and Ib.