Korean and Japanese isolates of viral hemorrhagic septicemia virus from olive flounder are pathogenic to rainbow trout fry

Abstract

We evaluated the pathogenicity of Korean and Japanese isolates of viral hemorrhagic septicemia virus (VHSV: genotype IVa) from olive flounder Paralichthys olivaceus using rainbow trout Oncorhynchus mykiss fry. The cumulative mortalities of fish challenged with FYeosu05 (Korean) and Obama25 (Japanese) isolates at 10 6.5 TCID 50/fish were 64 and 48%, respectively. No mortality was observed among the fish challenged with either of the isolates at 10 5.5 TCID 50/fish, or in mock-challenged fish. The affected fish exhibited darkening of the body, an expanded abdomen, pale gills, an enlarged spleen, and diffuse necrosis in the splenic and interstitial hematopoietic tissues. We re-isolated VHSV from all mortalities using cell culture and confirmed their presence by reverse transcription loop-mediated isothermal amplification (RT-LAMP). We thus concluded that Asian VHSV isolates from olive flounder are pathogenic to rainbow trout fry, although with low virulence.