Viremia-associated ana-aki-byo, a new viral disease in color carp Cyprinus carpio in Japan

A new virus disease that displays dermal ulceration and high mortality has been occurring since 1996 in color carp Cyprinus carpio reared in warm water in Japan. In histological examinations, initial erosive lesions displayed necrosis, hemorrhage and fibrin deposition in the dermal loose connective tissue and were accompanied by the partial destruction of the epidermis. Developed ulcerative lesions involved the lateral musculature with bacterial invasions. In visceral organs, necrotic cells were observed in the hematopoietic tissue, the spleen and the intestinal tissues as well as in cardiac muscle fibers which showed no signs of bacterial invasion. Electron microscopy revealed corona-like virus particles in these necrotic cells. The necrotic cells of the hematopoietic tissue and the spleen were accompanied by the formation of tubular structures and crystalline inclusions. The putative virus was isolated and cultured in epithelioma papillosum cyprini (EPC) cells. Carp experimentally inoculated with the cultured virus showed virus transmission, and the same pathological signs of the disease and mortalities as in natural infections.