DAO 101:105-114 (2012)  -  DOI: https://doi.org/10.3354/dao02503

Genetically similar VHSV isolates are differentially virulent in olive flounder Paralichthys olivaceus

Mi Young Cho1,*, Unn Hwa Lee2,*, Chang Hoon Moon3, Jong Deuk Bang1, Bo Young Jee1, Seung Ju Cha1, Jin Woo Kim1, Myoung Ae Park4, Jeong Wan Do4,**, Jeong Woo Park2,**

1Aquatic Life Disease Control Division, National Fisheries Research and Development Institute, Busan 619-705, South Korea
2Department of Biological Sciences, University of Ulsan, Ulsan 680-749, South Korea
3Biomedical Research Center, Ulsan University Hospital, University of Ulsan College of Medicine, Ulsan 682-060, South Korea
4Division of Pathology, National Fisheries Research and Development Institute, Busan 619-705, South Korea
*These authors contributed equally to this work
**Corresponding authors. Email: ;

ABSTRACT: Two viral hemorrhagic septicemia virus (VHSV) isolates, VHSV-KR-CJA and VHSV-KR-YGH, were isolated from viral hemorrhagic septicemia disease outbreaks in flounder farms in South Korea. The VHSV-KR-CJA isolate was isolated from a flounder farm with high mortality (80%), while the VHSV-KR-YGH isolate was isolated from a flounder farm with low mortality (15%), suggesting that these isolates differ in virulence. The virulence of these isolates was evaluated in juvenile flounder via intraperitoneal injection. Consistent with their virulence in the field, mortality data revealed that the VHSV-KR-CJA isolate was highly pathogenic (cumulative mortality of 80%), while the VHSV-KR-YGH isolate was less pathogenic in flounder (cumulative mortality of 20%). To characterize the genotypes of these viruses, the full open reading frames (ORFs) encoding nucleoprotein N, phosphoprotein P, matrix protein M, glycoprotein G, nonstructural viral protein NV, and polymerase L of these viruses were sequenced and analyzed. Sequence analysis revealed that both isolates are genetically very similar (identical amino acid sequences for P, M, NV, and L and >99.7 and 99.8% amino acid sequence identity for N and G, respectively). Phylogenetic analysis indicated that both of these viruses belong to the Genotype IVa group, suggesting that they originated from a common ancestral virus. The low pathogenicity VHSV strain may potentially evolve to become a more pathogenic strain through only a few nucleotide substitutions. Further functional analyses of mutations in VHSV genes are necessary to identify factors that determine VHSV pathogenicity in flounder.


KEY WORDS: Viral hemorrhagic septicemia virus · VHSV · Virulence · Flounder


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Cite this article as: Cho MY, Lee UH, Moon CH, Bang JD and others (2012) Genetically similar VHSV isolates are differentially virulent in olive flounder Paralichthys olivaceus. Dis Aquat Org 101:105-114. https://doi.org/10.3354/dao02503

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