Bovine tuberculosis resulting from infection with Mycobacterium orygis in a closed herd of Indian water buffalo (Bubalus bubalis)

Mycobacterium orygis (M. orygis), a member of the Mycobacterium tuberculosis complex, has emerged as an important cause of animal and human tuberculosis in South Asia. Despite the widespread prevalence of bovine tuberculosis (bTB) in India and the major role of over 100 million Indian water buffaloes in dairy production, the pathological and epidemiological features of M. orygis infection in buffaloes are largely unexplored. A closed herd of 279 female water buffaloes in Haryana, India, was screened for bTB by single intradermal cervical tuberculin skin (SCT) test, the comparative cervical tuberculin (CCT) test, and the interferon gamma release assay (IGRA). Detailed post-mortem examinations, cultural isolation, Polymerase Chain Reaction, and Whole Genome Sequencing were methodically performed on reactor buffaloes. The screening identified 26 animals as reactors by SCT. Of these, 20 were confirmed positive for bTB with both CCT and IGRA. Among the 15 reactor animals examined, gross pathological lesions suggestive of bTB were observed in 13 animals, while histopathological lesions in 14 animals. Molecular analyses confirmed the presence of MTBC in nine animals, with eight identified as M. orygis infections and one with mixed infection. Notably, two genetically distinct clusters of M. orygis suggestive multiple introductions into the herd. The study reveals significant pathological and microbiological complexities in bTB infections by M. orygis in Indian water buffaloes. It underscores a need for expanded research, improved surveillance, and introduction of targeted control measures to eliminate bTB in this major farmed animal species.