Pulmonary tuberculosis in captive sloth bear (Melursus ursinus) due to Mycobacterium tuberculosis

An adult male captive sloth bear died after prolonged illness at Mahendra Chaudhary Zoological Park, Chhatbir, Punjab. The sloth bear, prior to death exhibited anorexia, progressive emaciation and signs of respiratory distress. Post-mortem examination revealed rough body coat, pale mucous membranes and debilitated body condition. Grossly, the lungs showed multicentric, poorly demarcated variable sized nodules which on sectioning revealed cavitations filled with semi-liquid pale-white material. Spleen, liver and kidneys were congested. Histopathological examination of the lung sections revealed diffuse granulomas comprised mainly of macrophages and alveoli were filled with liquefied caseum composed of mixed population of degenerated inflammatory cells. The duplicate sections of lungs were positive for acid-fast bacilli in Ziehl-Neelsen (ZN) staining. Immunohistochemical staining of the lungs sections with anti ESAT-6 and CFP-10 antibody revealed moderate to intense positive signals in the liquified caseum. M. tuberculosis was confirmed as the causative agent by 12.7 kb gene, 16S rRNA and MPB70 gene segment and region of difference (RD 4 and 9) based PCR along with the cultural isolation on L-J media. Tuberculosis (TB) in the animal was diagnosed with the help of ZN staining, histomorphological lesions, immunohistochemistry, PCR and cultural isolation of Mycobacterium tuberculosis. The present case report confirmed M. tuberculosis as the cause of TB in the sloth bear which is having histomorphological lesions very similar to the post primary TB in humans.