NUCLEOCAPSID GENE SEQUENCE OF A NORTH-AMERICAN ISOLATE OF VIRAL HEMORRHAGIC SEPTICEMIA VIRUS, A FISH RHABDOVIRUS

Viral haemorrhagic septicaemia is the most important viral disease of trout in Europe. The causative agent, viral haemorrhagic septicaemia virus (VHSV), a member of the lyssavirus genus of the rhabdoviridae family, was formerly believed to be confined to portions of the European continent; however in 1988, VHSV was isolated from adult chinook (Oncorhynchus tshawytscha) and coho (O. kisutch) salmon returning to two hatcheries in the northwestern part of the State of Washington, U.S.A. Initial fears were that the virus had been imported into North America, perhaps by aquaculture activities. The nucleotide and deduced amino acid sequences of the nucleocapsid (N) gene of one of the North American (Makah) isolates of VHSV were determined and compared with published sequences of a European reference strain of VHSV (07-71) and the Round Butte strain of infectious haematopoietic necrosis virus (IHNV), another salmonid fish rhabdovirus that is enzootic in western North America. The N gene of the Makah isolate of VHSV shared a similarity of 88.433% at the nucleotide level and 94.802% at the amino acid level with the N gene of the European strain of VHSV, and 62.121% amino acid similarity with the N protein of IHNV. Like the European reference isolate, the North American isolate of VHSV showed three domains in the N protein, the central one being the most conserved and the likely site of interaction with genomic RNA. This was also the region of highest similarity with the amino acid sequence of IHNV. The sequence that suggested that the Makah and 07-71 isolates were of independent origin.