Identification of viral hemorrhagic septicemia virus isolated from Pacific cod Gadus macrocephalus in Prince William Sound, Alaska, USA

Abstract

Ulcerative skin tissues from 2 Pacific cod Gadus macrocephalus caught in Prince William Sound, Alaska, USA, were examined for virus by Fish Pathology staff within the F.R.E.D. Division of the Alaska Department of Fish and Game. Six days after inoculation of Epithelioma papulosum cyprini (EPC) cells at 14 degree C, diffuse rounding and lifting of cells from the monolayers suggestive of cytopathic effect became visible in the lower sample dilutions. Ultrastructural examinations of affected EPC cells showed rhabdovirus particles within cytoplasmic vacuoles and on the cell surface membranes. Virus isolates from both cod were subsequently confirmed as viral hemorrhagic septicemia virus (VHSV) by serum neutralization and immunoblot assay. This is the first VHSV isolated from Pacific cod, which represents a new host species for the virus. Histologically, cod skin ulcers appeared to be caused by a foreign-body-type inflammatory response to foci of protozoa resembling X cells that also had plasmodial stages. Whether the rhabdovirus was incidental to the skin lesion or played a role in its etiology remains to be determined. The possible relationship between this virus and the recent occurrences of VHSV in anadromous salmonids from Washington State, USA, is discussed.