Abstract
The spotted knifejaw (Oplegnathus punctatus) is an emerging economical aquaculture species in China in recent years. In the present study, we characterized an iridovirus-like disease outbreak in spotted knifejaw aquaculture industry in Shandong Province (SKIV-SD), China. SKIV-SD induced severe cytopathic effect (CPE) in spotted knifejaw brain (SKB) cells as the infection proceeded. Moreover, electron microscopic observation showed the abundant hexagonal virus particles of ~140 nm in diameter in the cytoplasm of infected SKB cells. After challenge with SKIV-SD, the cumulative mortality rate was up to 100% at 9 days post-infection. And the diseased spotted knifejaw displayed pathognomonic microscopic lesions, demonstrated by basophilic cytoplasmic inclusions in spleen and kidney which was a general sign of megalocytivirus infection. Using Illumina NovaSeq system, we assembled the sequence data, and annotated the full genome of SKIV-SD, which was composed of 111,198 bp and contained 116 ORFs. Phylogenetic analyses based on 4 iridovirus core genes, including major capsid protein (MCP), myristylated membrane protein (MMP), DNA polymerase and ribonuclease III genes indicated that SKIV-SD shared the nearest relationship to infectious spleen and kidney necrosis virus (ISKNV). Moreover, the genome co-linearity analysis indicated that the gene orders and gene spacing of 25 iridovirus core genes were conserved between SKIV-SD and ISKNV. Together, our data speculated that SKIV-SD, an ISKNV-type megalocytivirus, was a lethal viral pathogen to cultured spotted knifejaw.
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