Isolation of a new virus from chinook salmon (Oncorhynchus tshawytscha) in Oregon U.S.A

A new virus has been isolated from adult chinook salmon (Oncorhynchus tshawytscha) in the state of Oregon, U.S.A. The virus was recovered from pooled kidney and spleen tissue samples using CHSE-214 cells. Cytopathic effect (CPE) required 28 days to develop on primary isolation. The virus replicated in CHSE-214, CHH-1, KO-6, CSE-119 and FHM cells. It had an optimal growth temperature of 18°C and no virus was produced at 24°C or above. The virus was stable in minimal essential medium (MEM) at pH 3-11 and replication was not affected in cells incubated with MEM containing 50μg/ml iododeoxyuridine. Infectious virus was recovered from fractions of a CsCl gradient having a density of 1.20 g/cc. The agent was sensitive to chloroform and caused hemagglutination with erythrocytes from several species of fish, mammals and birds. Electron microscopy revealed enveloped particles 125-250 nm in diameter containing a coiled nucleocapsid. Electron micrographs of freon-treated preparations showed the extracted nucleocapsid to be a helix 18 nm in diameter and up to 1000 nm in length. Based on morphology and biochemical features, the virus appears to be a member of the Paramyxoviridae.