Mycobacteriosis is the oldest known infectious disease of reptiles that is caused by bacteria of the genus Mycobacterium. This genus comprises over 100 species of bacteria, including the obligate pathogenic, potentially pathogenic mycobacteria and environmental saprophytic mycobacteria. There are some reports on the incidence of mycobacterial infections in different types of turtles in the world. Only two studies have been conducted on mycobacterial infections of some ornamental fishes in Iran. To the authors, knowledge, there is no study on the mycobacteriosis of Caspian turtles in the country. The aim of this study was to describe macroscopic and microscopic lesions of the disease for the first time in Iran. The livers of two Caspian turtles which were collected from southern basin of the Caspian Sea in Mazandaran province were referred to Department of Pathology, Faculty of Veterinary Medicine, Ferdowsi University of Mashhad due to presence of focal hepatic lesions. After recording of gross characteristics, for histopathological study, tissue samples were taken from the lesions, fixed in buffered formalin solution and processed through routine paraffin embedding technique. They were cut at 5 μm and stained by hematoxylin and eosin and Ziehl-Neelsen methods. Macroscopically, a large number of white foci with different sizes were observed in the affected livers. Histopathological examinations revealed focal granulomatous inflammation throughout the livers of both turtles. There were macrophages in the central parts of the lesions and lymphocytes and plasma cells in the periphery of them. The central areas of some nodules had caseous necrosis that was surrounded with multiple giant cells. A lot of mycobacterial rods were observed in the some central necrotic regions by Ziehl-Neelsen staining method. The results of this study showed that Mycobacterial spp. can cause mycobacteriosis and associated liver lesions in Caspian turtles and should pay attention to this disease as important health problem in this species.

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