Comparative study of experimental mycobacteriosis between snakehead fish (Chana striata) and frog (Rana tigrina)

摘要

In many of the culture areas in Thailand, snakehead fish suffer mortality from septicemic mycobacterium infections (Chinabut et. RAID., 1990). The contaminated drainage from fish farms may spread into the environment and potentially cause problems to frog hatcheries and growout farms. A total of 80 fish and 160 frogs were intramuscularly injected with a pure cultured virulent strain of M. marinum, isolated from the kidney of a diseased snakehead fish with clinical signs of mycobacteriosis. The inoculated animals were observed daily for the appearance of clinical signs of infection and were sacrificed routinely for the pathological study. After 15 days of injection, the infected fish showed emaciation, lack of coordination, erosion of fins, scale loss and severe ulceration, whereas the infected frogs did not show any gross pathological lesions throughout the experiment. Gray-white miliary tubercles were observed in the spleen, kidney and liver of the infected fish whereas these tubercles were never found in any organs of infected frogs. Histologically, the granulomatous inflammation was observed both in fish and frogs. Granulomas found in the visceral organs, dermis and injected areas of fish and in the injected areas of frogs revealed the composition of epithelioid and phagocytic cells surrounded by whorls of fibroblastic cells. Central caseous necrosis was observed only in fish granulomas. Two different cell types were noticed in frog skin in the early period of the experiment. The dark elongated nuclear cells resembling mammalian Langerhans cells were observed in the suprabasal epidermis, and the stellate shaped dendritic cells were observed both in the dermis and hypodermis. Both cell types are reported with reference to delayed-hypersensitivity in humans.