Development of an effective DNA vaccine against ayu atypical cellular gill disease using draft genome information of the causative agent, Plecoglossus altivelis poxvirus

Atypical cellular gill disease (ACGD) in ayu (Plecoglossus altivelis) caused by P. altivelis poxvirus (PaPV) infection has led to significant economic losses in Japanese aquaculture. The propagation of PaPV has not yet been successfully achieved in cultured cells. In this study, we sequenced a draft genome of PaPV and developed an effective vaccine against the disease based on this genomic information. The draft genome of PaPV, obtained from a diseased fish in 2016, was constructed using sequence data from an Illumina MiSeq analysis. The genome comprised 376,224 bp, including a 14,355 bp inverted terminal repeat at both ends, with a G + C content of 28.3 % and 353 predicted open reading frames (ORFs). Phylogenetic analysis using 13 core genes conserved across Poxviridae revealed that PaPV clusters with other fish poxviruses, including carp edema virus and salmon gill poxvirus, within the subfamily Chordopoxvirinae. The protective efficacy of a formalin-killed virus vaccine and DNA vaccines targeting ORF226 (vaccinia virus L1R homolog) and ORF227 (vaccinia virus D13L homolog) was evaluated. The DNA vaccine targeting ORF227 provided a high survival rate following virus challenge, whereas the formalin-killed vaccine resulted in lower survival. Gene expression analysis suggests that the effective DNA vaccine against ACGD likely induces cell-mediated immunity in the gills.