Abstract
Among survivors of experimental infection of herpesvirus OMV which was considered to be a new viral pathogen of salmonids producing hepatic necrosis and significant mortality, more than 60% developed tumors. The perioral maxillary and mandibular region are the most frequent site of tumor formation. In decreasing order of frequency, tumors were also found on the caudal fin, gill-cover, eye, and kidney.
Histopathologically the tumors were composed of abundantly proliferative, well differentiated epithelial cells supported by fine connective tissue stroma.
Although virus particles were not observed in tumor cells, OMV isolation was successful from a tumor tissue sample that appeared necrotic on day 275 postinfection and from primary cultures of a tumor tissue from another fish sampled 296 days postinfection.
From the evidence thus far obtained, OMV is considered to be a new pathogenic and oncogenic salmon virus.
It is the first oncogenic agent to be isolated from fish.
