Pathological and molecular characterization of Mycobacterium tuberculosis complex in necropsied tissues of sambar deer (Rusa unicolor) and nilgai (Boselaphus tragocamelus) from Assam state, India.

Bovine tuberculosis is a chronic bacterial disease primarily caused by Mycobacterium bovis, a member of the Mycobacterium tuberculosis complex (MTBC), with significant zoonotic implications. This study aimed to detect MTBC in wildlife species, specifically nilgai (Boselaphus tragocamelus) and sambar deer (Rusa unicolor), using gross pathology, histopathology, acid-fast staining, and molecular confirmation. Necropsied tissue samples were collected during post-mortem examination of a nilgai and a sambar deer from the Assam State Zoo, Guwahati, India. Macroscopically, multiple granulomatous tubercles of varying sizes were observed in the lungs and liver, with creamy white caseous material marked upon sectioning. Ziehl-Neelsen staining of the tissue smears from granulomatous lesions confirmed the presence of acid-fast bacilli. Microscopic examination of tuberculosis granulomas revealed a central necrotic mass surrounded by inflammatory cell infiltration, including Langerhans-type giant cells. Molecular confirmation of MTBC infection was achieved by amplifying hsp65 and IS1081 in tissue samples, further validated by Basic Local Alignment Search Tool for nucleotide analysis following Sanger dideoxy sequencing. In conclusion, this study confirmed the presence of tuberculosis in these wildlife species through an integrated approach combining pathology, microbiology, and molecular diagnostics, highlighting the need to understand pathogen entry into the herd and prevent potential spillover.