Oncogenicity of fish herpesvirus and protective immune mechanisms of fish

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Biological, serological and genetical relationships of three salmonid herpesviruses (strain H-83, Oncorhynchus masou virus (OMV) and Herpesvirus salmonis) were investigated.The strain H-83 was pathogenic to masu salmon and rainbow trout fry, however, yearing fish were not sensitive. The fish produced virus-neutralizing antibody with low titers, and the expression of secondary immune response was observed.Coho salmon fry infected with OMV developed tumors in and around the oral cavity. The results of virus re-isolation indicated that the liver was the target organ of OMV infection.Cross enzyme-linked immunosorbent assay and cross neutralization test revealed that strain H-83 and OMV were serologically similar but different from H.salmonis.DNA-DNA hybridization test also suggested the presence of many more homologous DNA sequences between strain H-83 and OMV DNAs than between them and H. salmonis.Restriction endonuclease cleavage pattern of strain H-83 DNA was similar to that of OMV but distinct from that of H. salmonis. After passages of the viruses for more than 33 times in vitro, some fragments appeared or disappeared, however, no DNA fragment of H. salmonis changed during the passages. The former two viruses showed a decrease in virulence in fry after passages.