1989 Volume 24 Issue 1 Pages 17-21
Epizootics and histopathology of BKD (Bacterial kidney disease) due to Renibacterium salmoninarum which occurred in sea-cultured coho salmon (Oncorhynchus kisutch), in northern coastal water of Miyagi Prefecture, were described. The death due to the disease was recorded from Jan. to July, 1987.Fish dying from BKD were collected from the floating net pens in May, 1987.
As the external clinical signs of BKD, skin ulcers, necrosis of the trunk muscle and thickness of the epicardium were recognized, but numerous white granulomatous lesions in the kidney could not be seen clearly. Histopathological examination showed that mononuclear cells which phagocyted the bacteria infiltrated into various organs, and inflammatory lession compressed the parenchymall tissue. But granulomatous inflammation could not be seen in organs other than the liver. The bacteria were electro microscopically found in lysosome of macrophage-like cells. However, no bacteria could be found in parenchymalcells.
As a result, the infectious mechanism was thought as follows : The bacteria first infected the injured skin to make lesions in muscle and penetrated into the blood vessel with macrophage-like cells, and finally reached the various organs. The cause of death was considered to be the decline of the systemic condition and particularly heart failure due to bacterial infection. But, furthermore, the detailed route of the infection should be studied in a future.
