A Fish Nodavirus Isolated from Cultured Sevenband Groupe, Epinephelus septemfasciatus

양식 능성어로 부터 Fish Nodavirus 분리

Since 1989, mass mortality has repeatly occurred in cage-cultured sevenband grouper, Epinephelus septemfasciatus along the southern coast of Korea in the summer season and usually reached over 80% within a few months. Diseased fish showed the clinical signs of anorexia, dark coloration, loss of eqilibrium, spinal swimming behaviour, vertebral deformity and inflation of swim bladder. Histopathologically, necrosis and/or vacuolation of the nerve cells in the brain and retina were observed. We previously reported that the causative agent was filtrable. The causative agent was not culturable in various fish cells; RTG-2, CHSE-214, BF-2, EPC and FHM. However, electron microscopic observation revealed unenveloped icosahedral viral particles with about 30 nm in diameter in the cytoplasm of nerve cells of the brain. The characteristics of the virus was tested by an artificial infection with the filtrate of the homogenate of diseased fish. The pathogenicity of the virus was retained after treatment with ether or heat ($50^{\circ}C$, 30 min) but partly lost by pH 3 or 11 treatment. These results suggest that the causative agent are similar to the fish nodavirus. In order to compare the causative agent with a fish nodavirus, Striped Jack Nervous Necrosis Virus (SJNNV), a polymerase chain reaction (PCR) was performed with primers specific to SJNNV. As a result, about 430 by PCR products were detected from the brain and the eye of both naturally and artificially infected sevenband grouper. All these results represent that the mass mortality in the cultured sevenband grouper is caused by the infection of a nodavirus similar to SJNNV and this is the first report of a fish nodavirus from the cultured sevenband grouper in Korea.

1989년부터 남해안 일원 해상 가두리 양식장에서 사육중이던 능성어가 고수온기에 대량폐사하여 폐사율이 80%이었다. 발병한 병어는 채색흑화, 안구돌출, 평행감각 상실,회전운동과 몸통이 휘어지는 증상을 나타냈고, 조직학적으로는 뇌조직 및 안구망막의 신경세포가 공포 또는 괴사되었다. 병어로 부터 어류주화세포를 이용한 세포배양법으로 원인 바이러스는 분리되지 않았지만, 뇌 신경세포의 세포질에서 크기가 약 30 nm이며 외막(envelop)이 없는 다면체 모양의 바이러스 입자가 전가현미경적으로 관찰 되었다. 능성어로 부터 분리된 바이러스는 에테르나 열($50^{\circ}C$, 30분)처리에 의해 병원성이 실활되지 않았으나, 강산(pH 3)이나 강알카리(pH 11)에는 부분적으로 병원성이 실활되었다. 그리고 fish nodavirus인 Striped Jack Nervous Necrosis Virus(SJNNV)의 primer를 이용하여 인위감염 및 자연감염된 능성어를 대상으로 PCR을 한 결과 감염된 능성어의 뇌 및 안구조직에서 악 430 bp정도의 PCR 증폭산물이 검출되므로서 능성어를 폐사시키는 원인 바이러스는 SJNNV와 아주 유사한 nodavirus 였다.