Pathology of naturally occurring paratuberculosis in water buffaloes (Bubalus bubalis).

Gross and histologic lesions of paratuberculosis were studied in water buffaloes. Small intestines and associated mesenteric lymph nodes of 405 water buffaloes were examined. Of these, 20 animals having visible changes of intestinal thickening, mucosal corrugations, and enlargement of mesenteric lymph nodes exhibited histologic alteration characteristics of mild to moderate granulomatous inflammation. The histologic lesions observed in these animals were classified into 3 grades on the basis of type of cellular infiltration, granuloma formation, and presence of acid-fast bacilli. Grade-1 lesions observed in 8 animals were marked by the presence of scattered epithelioid macrophages amid large number of lymphocytes in the intestinal villi and in the paracortical regions of the associated mesenteric lymph nodes. Another 8 animals classified under grade-2 revealed microgranulomas, infiltration with a larger number of epithelioid macrophages besides lymphocytes in the intestinal villi, and granulomas in the mesenteric lymph nodes. Grade-3 lesions observed in 4 animals were characterized by the presence of epithelioid granulomas and giant cells in the intestines and the mesenteric lymph nodes. The Ziehl-Neelsen's stained tissue sections revealed acid-fast bacilli in grade-3 and -2 animals and acid-fast granular debris in grade-1 animals. Among these 20 buffaloes, 14 (70%) were positive in the IS900 specific polymerase chain reaction and 6 (30%) were positive in the bacterial culture.