Pathogen Oncorhynchus masou virus: OMV
Taxonomy Herpesviridae
Hosts Salmonid fishes including masu salmon (Oncorhynchus masou) and coho salmon (O. kisutch).
Disease name Viral rerioral basal cell epithelioma
Infection site Mouth
Clinical signs Epithelial tumors are formed around the jaw (Fig. 1).
Virology The pathogen is a DNA virus having a hexagonal capsid (ca. 100 nm in diameter) and an envelope (220-240 nm). It shows distinctive CPE i.e. marked syncytium formation when incubated with the cell derived from salmonid fish. The suitable temperature for proliferation is 10-15.C. and it is inactivated more than 20 C. (Yoshimizu, 2004).
Pathology Though diseased fish exhibits tumors (basal cell carcinoma) around the head and jaw, the disease is not fatal.
Health hazard Since this virus is not infectious to human, it is harmless in food hygiene.
Diagnosis Presumptive diagnosis can be performed by the clinical signs. It is needed for definitive diagnosis to check the CPE and confirm the identification by a serological or PCR method after virus isolation.
Other information This disease is known as the first case which a fish tumor is experimentally produced for the first time. Recently, the disease hardly occurred since quarantine management is thoroughly practised.

Yoshimizu, M (2004): Viral diseases Infectious and parasitic diseases of fish and shellfish. (ed. by Wakabayashi, H. and K. Muroga), Koseisha Koseikaku, pp.29-128. (In Japanese)

(Photo by T. Awakura)

Fig. 1. Epithelioma caused by OMV