Phylogenetic analysis and duplex RT-PCR detection of viral hemorrhagic septicemia virus in olive flounder (Paralichthys olivaceus) from Korea

Abstract

Viral hemorrhagic septicemia is a serious disease that can assume epidemic proportions in cultivated olive flounders in Korea. The causal agent of this disease is viral hemorrhagic septicemia virus (VHSV), and it leads to vast economic losses in the olive flounder aquaculture industry. Therefore, the rapid and accurate detection of VHSV is paramount. At present, the manual of the World Organization for Animal Health's Office International des Epizooties (OIE) for pathogen detection is being followed for VHSV detection in Korea. However, in that manual, the primers for VHSV detection are based on the European VHSV genotype Ia. In this study, we identified 5 VHSV strains from olive flounders in Korea, and the nucleotide and amino acid sequences of VHSV genes (N, P, M, and G) were compared to investigate the genetic variation of VHSV genotypes. As expected, VHSV isolates from Korea were highly related to genotype IVa, clearly differing from the 3 European genotypes. In addition, the N gene showed low genetic variation and therefore might be considered a useful marker for VHSV detection, regardless of genotype. In contrast, the other VHSV genes (P, M, and G) had different nucleotides within genotypes. They might be suitable for designing specific primers for distinguishing between various VHSV genotypes. Duplex RT-PCR using the newly designed primers successfully detected all VHSV isolates and validated the genotype (I and IV) without sequence analysis. According to the results, all the VHSV isolates were successfully detected, and their genotypes were validated by duplex RT-PCR using the newly designed primers. Collectively, our findings suggest that duplex PCR is a convenient and appropriate method for the diagnosis of VHSV isolates in Korean aquaculture systems.