Tuberculosis as Zoonosis

Tuberculosis (TB) in humans caused by Mycobacterium tuberculosis is still a threatening disease worldwide. In domestic animals' cases, the pathogen is usually Mycobacterium bovis, however, other M. tuberculosis complex (MTC) lineages are sometimes observed. Especially, in Asian elephant cases, the major TB pathogen is the human type, M. tuberculosis. In Nepal, we analyzed several elephant MTC isolates and found that they were M. tuberculosis possessing Nepalese isolate specific features suggesting the animals were infected by their handlers. Bovine TB control is a serious problem in many countries including some developed countries. The failure of its control is mainly caused by the wide host range of M. bovis. Once the bacteria adopt to wild mammalian species, the eradication becomes very difficult. However, in most of the developing countries, detailed surveys on bovine TB have not been carried out, although they have noticed the existence of the disease. In Bangladesh and Nepal, we analyzed MTC isolates obtained from cattle and wild animals, namely, two monkeys, a deer, an antelope and a rhino, and found all of them were belonging to a newly identified MTC subspecies, M. orygis. Their genetic diversity suggested the introduction of the pathogen was not a recent event in those areas. TB lesions were observed in lungs in all the cases suggesting air-borne transmission of the pathogen. Several human TB cases by M. orygis have been reported and most of them were from South Asia. Thus, TB cases in animals in South Asia might be caused by M. orygis, rather by M. bovis. Treatment regimens are different among MTC subspecies, thus, the identification of the species is important. Since the pathogen of animal TB in South Asia might be different from other areas and the pathogen, M. orygis, seems to have a wide host range, continuous surveys seem to be necessary to know the situation. To monitor the possible emerging disease in humans, the development of easy, rapid and low-cost screening methods is important.