Histopathological Studies on the Furunclosis of Amago—III

Percutaneous Infection

Abstract

Naturally diseased amago (Oncorhynchus rhodurus f. macrostomus) with swellings of cutaneous erosions or ulcers was histopathologically examined. The following histopathological observations were made. 1) An early stage of infected lesions in the loose connective tissue of the derm showing small bacterial colonies and marked serous-fibrinous exudation, 2) infected lesions in the dence connective tissue of the derm showing degeneration of the tissue and infiltration of mononulear cells, 3) other infected lesions extending through the adipose tissue to the musculature with drastic bacterial dissemination and multiplication in the interstitial tissue, with marked tissue destruction accompanied by hemorrhage and serous-fibrinous exudation, and with mononuclear infiltration and less conspicuous neutrophilic emigration, and 4) metastatic lesions ensuing in visceral organs with small or large bacterial colonies and tissue destruction.
From these histopathological observations, we concluded that with this type of diseased fish Aeromonas salmonicida entered the fish through the skin. Especially the lesion with swellings proved to be formed not by suppurative exudation but by the secondary liquefactive digestion of the tissue affected by bacterial infection, provided that the character of the fish nutrophilics was the same with that of the human ones. We also think that bacterial cells were generally disseminated as an infected lesion spread through the musculature and developed into a septicemic lesion, which further caused a secondary septicemia.