Granulomatous hepatitis in cattle caused by Mycobacterium avium subsp. paratuberculosis

Samples from intestines, liver, and lymph nodes were collected from a dairy steer with clinical suspicion of paratuberculosis. The samples were processed for histologic examination with hematoxylin-eosin and Zihel-Neelsen (ZN) staining for the detection of acid-fast bacilli (AFB), and submitted to immunohistochemistry (IHC). Macroscopic changes were observed in the small intestines, with thickening and corrugation of the mucosa. The main microscopic changes were found in small intestines, lymph vessels in the mesentery, and mesenteric lymph nodes characterized by enteritis, lymphangiectasia, and lymphadenitis. Liver presented with granulomatous hepatitis, an uncommon histopathological feature for paratuberculosis. The clinical features associated with positive culture of Mycobacterium avium subsp. paratuberculosis and detection of AFB by ZN and IHC in the cytoplasm of macrophages (epithelioid) in the intestinal mucosa and submucosa, lymph nodes, and liver were important to confirm the diagnosis of paratuberculosis.