Abstract
A disease showing erosive and ulcerative cutaneous lesions occurred in Japanese eels Anguilla japinica, reared in warm-water ponds in the spring of 1992. In this study, virological investigation, histological and electron microscopic observations were performed in both naturally and experimentally infected eels. A herpesvirus was isolated from the skin lesions and EK-1 cells inoculated with the isolated virus formed polynulcear giant cells at 25°C within 2 days after inoculation. The isolate was neutralized with an anti-Herpesvirus anguillae serum. Electron microscopy revealed enveloped virions with a diameter of 200nm in the cytoplasmic vesicle and nucleocapsids with a diameter ranging 114-115nm in nuclei of infected EK-1 cells. In experimental infections, the isolate did not have lethal effect on eels during rearing period of 14 days at 25°C. However cutaneous lesions were produced at the inoculated sites. Histologically, the cutaneous lesions of naturally as well as experimentally infected fish, showed similar signs : fibrocytes in the dermis were infected and necrotized, accompanied with necrotic changes of melanocytes and subsequent infiltration of inflammatory cells. The fibrocytic necrosis and the infiltration of inflammatory cells extended into the subcutaneous adipose tissue and lateral musculature.
