Bovine tuberculosis: a potential public health risk in Nepal

[PHP Nepal Vol 3 Issue 3 Mar 2013] | According to the 2012 Global Tuberculosis Report of World Health Organization (WHO), there were an estimated 8.7 million new cases of Tuberculosis (TB) and 1.4 million deaths in the world in 2011. Geographically, the burden of TB is highest in Asia and Africa and almost 60% of cases are in the South East Asia and Western Pacific regions. As per the annual report (2010/11) of National Tuberculosis Control Program (NTP), in Nepal, 35,964 cases of tuberculosis were registered from mid July 2010 to mid July 2011.

Similarly, between 5,000 to 7,000 deaths occurs in the country each year due to TB. Though progress has been made towards global targets for reductions of tuberculosis cases and deaths, the burden still remains enormous due to TB/HIV co-infection and drug resistant TB.

Mycobacterium tuberculosis is the most common cause of human TB but certain proportion of cases is due to Mycobacterium bovis (a bacterium responsible for bovine TB). Infection of bovine TB (bTB) occurs mainly through consumption of contaminated, unpasteurized milk or dairy products. Infection can also occur from direct wound contact as in case of slaughtering of buffalo and cattle or by inhaling the bacteria in air exhaled by infected animals or also through consumption of meat products contaminated by M. bovis. TB caused by M. bovis is clinically indistinguishable from TB caused by M. tuberculosis which also includes fever, night sweats, and weight loss. M. bovis also causes TB that can affect the lungs, lymph nodes, and other parts of the body. As per the Nwanta et. al. (2010) review, the contribution of M. bovis accounted for 3.1% of all forms of human tuberculosis; 2.1% of pulmonary; and 9.4% of non-pulmonary forms in and the burden is likely to be higher in developing countries like Nepal. 

As per the Joshi et. al. (2012) report, the overall prevalence of bTB in buffalo and cattle were respectively 9.08% and 5.78% in Nepal. Since livestock is the indispensable part of our agricultural system, buffalo and cattle are often kept in very close vicinity or in the same dwelling owing to the lack of land or a shed for shelter. This increases the chance of spread of M. bovis. In a recent study by Pandey et. al. (2012), in Chitwan district, bTB prevalence in cattle and buffalo was found to be 15%. The study was carried out among the buffalo and cattle raised by tuberculosis clients who were under DOTS treatment. Raw milk consuming habit was also demonstrated in some of those TB infected farm family members. This raises suspicion over how TB was acquired – perhaps from animals or from else? 

In industrialized countries, animal TB control and elimination programs, together with milk pasteurization, have drastically reduced the incidence of TB disease caused by M. bovis in both cattle and humans. However, pasteurized milk and milk products consumption are not common among Nepalese especially among those living in rural areas. Besides, buffalo and cattle suffering from bTB are also slaughtered and sold in the market as we don’t have enough ante mortem and post mortem examination facilities. In addition, there are limited laboratory facilities in Nepal to determine the M. bovis contribution in human tuberculosis. Lack of awareness about bTB is the other issue. The situation is even aggravated by the limited reporting of bTB in animal populations, close human-animal interaction and lack of sufficient prevention practices surrounding animal tuberculosis.

In these circumstances, periodic screening of animals, provision of diagnostic laboratory facilities, enforcement of Animal Slaughterhouse Act and Meat Inspection Act (1999), proper coordination among human and animal health sectors and more importantly public awareness campaigns are recommended for better understanding and reducing the risk of acquiring bovine tuberculosis by humans.

Dr. Santosh Dhakal is a veterinary officer at National Zoonoses and Food Hygiene Research Centre in Kathmandu, Nepal.

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