Abstract
In December 1992, a disease characterized by cutaneous erosion and ulceration occurred in Japanese eels, Anguilla japonica, during the post-harvest stocking in cages showered with well water (15deg;C). Since then, this disease sometimes occurs and causes mass mortalities during the stocking before shipping.This study evaluated histological changes, virological characteristics and pathogenicity of an isolated virus from ulcerative lesions.Inocula prepared from the skin lesions, kidney and spleen of naturally diseased eels produced cytopathic effects in EK-1 and EPC cells at 15deg;C. Electron micrographs of infected EPC cells revealed virus virions with the average size of 188×70 nm. Replication of the virus was not inhibited by IUdR, but it was sensitive to ether. Serological tests showed a similarity of this isolate to two eel rhabdoviruses, EVA and EVEX. The isolated rhabdovirus had pathogenicity to eels by an intracutaneous injection at a viral level of 107 TCID50. Moribund fish of experimental infection displayed cutaneous lesions accompanied with necrosis of the dermal fibrocytes, hemorrhage and inflammatory cellular infiltration.These symptoms were similar to those of the natural cases. Moreover, moribund fish showed diffuse necrosis of the hematopoietic tissue, renal tubules, splenic pulps and hepatic parenchyma.The presence of virions in the above necrotic lesions was clearly observed by electron microscopy. We propose to designate this disease as rhabdoviral dermatitis in Japanese eel.
