Genetic relatedness among Japanese, American and European isolates of viral hemorrhagic septicemia virus (VHSV) based on partial G and P genes

Viral hemorrhagic septicemia (VHS) is the most serious viral disease of farmed rainbow trout Oncorhynchus mykiss in continental European countries.The causative agent of VHS has a widespread distribution in a variety of freshwater and marine fishes (Mortensen et al. 1999, Smail 1999).The first isolation of marine VHSV was from Atlantic cod Gadus morhua in 1979 (Jensen et al. 1979, Vestergård-Jørgensen & Olesen 1987), and subsequently outbreaks were reported in sea-farmed rainbow trout in France (Castric & de Kinkelin 1980), and turbot Scophthalmus maximus in Germany and Scotland (Schlotfeldt et al. 1991, Ross et al. 1994).In addition, VHSV has been isolated from several wild marine fishes, such as cod and herring Clupea harengus (Mortensen et al. 1999).The first American VHSV was isolated from returning chinook salmon O. tshawytscha and coho salmon O. kisutch in western North America in 1988 (Brunson et al. 1989, Winton et al. 1989).The same type of VHSV strains were isolated from Pacific cod G. macrocephalus, Pacific herring C. harengus pallasi and other marine fishes (Meyers et al. 1992(Meyers et al. , 1994(Meyers et al. , 1999)).On the other hand, VHSV has never been isolated from fishes in East Asian countries although distribution of other fish pathogenic novirhabdoviruses such as infectious hematopoietic necrosis virus (IHNV) and hirame rhabdovirus (HIRRV) were reported (Kimura & Yoshimizu 1991, Nishizawa et al. 1991).In 1999, VHSV was first isolated in Japan from wild Japanese flounder Paralichthys olivaceus during a survey on the distribution of fish viruses in wild marine fishes (Takano et al. 2000(Takano et al. , 2001)).Recently, rhabdoviral infections occurred in farmed Japanese flounder in the Seto Inland Sea of Japan and the causative agent was identified as VHSV (Isshiki et al. 2001).VHSV, a member of the genus Novirhabdovirus of the family Rhabdoviridae, has a single molecule of linear, negative-sense ss-RNA (approximately 11.1 kb) with 6 genes in the order 3'-N-P-M-G-NV-L-5' (Walker et al. 2000).The phylogenetic analysis based on the nucleotide sequences of the partial G gene of VHSV isolates from marine and freshwater fishes revealed 3 genogroups, I, II and III (Benmansour et al. 1997, Stone et al. 1997).The American isolates of VHSV from marine fishes are assigned to the Genogroup I while