Abstract:Pathological study on Scophthalmus maximus affected by an iridovirus in China revealed that the most prominent and consistent characteristics of this disease were the basophil enlargement of cells, mainly in the spleen, and also in the kidney, intestine, liver, gill, heart and skin. There were various pathological changes to the tissues associated with iridovirus. The spleen suffered the marked pathological changes with the heavy necrosis of hematopoietic tissue. In addition, necrosis of hematopoietic tissue in kidney, haemorrhage and oedema in submucosa of intestine, hydropic degeneration of hepatic cells, local necrosis of cardiac muscle and hemorrhage with inflammatory exudation in dermis were also observed. Electron microscopy showed that numerous viral particles were present in the enlarged cells. The viral particles were distributed in the cytoplasm, tissue interstice and lument of blood vessel. Cells infected by the virus presented obvious cytopathological changes. The mitochondria and endoplasmic reticulum fragmented and dissolved in the swollen cytoplasm. The haemorrhage in subcutaneous tissue with virus infection was responsible for the reddish appearance of diseased turbot. Anaemia caused by the virus infection was the main cause of death in affected fish and organ failure as a result of tissue necrosis also accelerated the death of diseased fish.
