Distribution of salmonid herpesvirus was known in USA and Japan. Herpesviruses isolated in USA were classified to serotype 1 (SaHV-1) and in Japan were serotype 2 (SaHV-2). The reference strain of SaHV-1 is Herpesvirus salmonis and SaHV-2 is Oncorhynchus masou virus (OMV) strain OO-7812. OMV disease (OMVD) causes oncogenic and skin ulcer conditions. The main susceptible fish species are kokanee salmon (Oncorhynchus nerka), masu salmon (O. masou), coho salmon (O. kisutch) and rainbow trout (O. mykiss). Economic losses caused by this virus were recognized among kokanee salmon, coho salmon and rainbow trout. At the beginning of the 1980s, OMV was distributed widely in the northern part of Japan. Since 1988, OMV was isolated from coho salmon and since 1991 this virus was found in rainbow trout. Recently, re-appearing OMVD has become a major problem in pond culture of rainbow trout in the central part of Japan. OMV is sensitive to ultraviolet irradiation and iodophore treatment. Although detection of OMV in carrier fish is difficult using polymerase chain reaction (PCR) and OMV replicates and appears in ovarian fluid at mature stage, it can be controlled by disinfection. OMVD was successfully controlled by disinfection of all facilities and eggs with iodophore just after fertilization and again at early-eyed stage
