Histopathological Studies of Edwardsiellosis of the Japanese Eel (Anguilla japonica)—II

Suppurative hepatitis form

Abstract

Histopathological studies were made on 9 diseased eels with suppurative hepatitis caused by Edwardsiella tarda infection. Fish in advanced stages of the disease showed a reddening of fins and the body surface and a swelling of the liver region of the trunk. Anatomically abscesses were observed in the liver, some of which were followed by the ulcer formation
The primary, detectable histopathological change in the liver was the appearance of micro abscesses containing macrophages phagocytizing bacteria in the sinusoids. As the disease progressed enlarged abscesses which were composed of a large number of juvenile neutrophils and necrotized hepatic cells and were thought to develop from the above-mentioned primary foci became more noticeable. Extensive lesions accompanied by liquefaction of abscesses and bacterial multiplication were found to involve large blood-vessels and in such cases metastatic necrotic lesions were observed in various parts of the liver and the hepatic cells were in an intensive fatty degeneration. While healing lesions demarcated by precipitated fibrin and newly formed granulation tissues were often observed. Peripheral extensive lesions often developed into ulcers and suppurative lesions were found in the region of the body musculature adjacent to large ulcers of the liver. In the stage of the generalized infection metastatic lesions were observed in the heart, gills and body musculature, and the spleen and the hematopoietic tissue of the kidney showed a cellular proliferativeinfiltrative reaction, and a marked hyperplastic reaction of the hematopoietic cells, respectively.