Bovine tuberculosis: a knotty problem?

Over the last decade HIV/AIDS has received much attention for its impact on sub-Saharan Africa but another disease receives far less press coverage and yet results in a much greater number of deaths each year. The disease in question? Tuberculosis.

credit: Dave Elsworth

Worldwide more than two million deaths occur each year as a result of tuberculosis and it is a particular problem in developing countries, especially in sub-Saharan Africa. Admittedly, HIV/AIDS has exacerbated the problem and, with the combined effect of increased drug resistance, more than 50,000 patients are diagnosed each year in Tanzania alone. However, two forms of the disease affect humans: pulmonary TB as well as bovine TB and it is not known how much the latter contributes to human infection. Indeed, until recently, the zoonotic role of bovine TB in developing countries received little attention. But, for the first time in Tanzania, veterinary and medical researchers have been brought together to collaborate on the impact of disease transfer from livestock to humans. And, although the project's focus was on Bovine Tuberculosis (Mycobacterium bovis) [BTB], the facilities and networks established in the country during the past few years can now be used to support research of other zoonotic diseases.

BTB is a key constraint to livestock production. Milk yields and draft power are reduced and infected carcasses are rejected for sale and consumption. In addition, the disease is not only a major cause of economic loss to farmers and butchers but it has a serious impact on export potential. However, most important is the risk of infection to humans, particularly for women and children who appear to be most susceptible to the disease.

A testing time

In 1996 the Government of Tanzania Veterinary Services identified the need to address the animal and human health problems that result from bovine TB, and a DFID-funded Animal Health* project was initiated to determine the prevalence of the disease and means of transfer from cattle to humans. Over the course of three years 10,000 cattle were tuberculin-tested by project vets in three districts in Arusha where the majority of farmers own only a few head of cattle. As a result of the testing, 14% of cattle were found to be infected with BTB, indicating that the disease is relatively widespread. On determination of the disease, the results were explained to farmers who were advised by veterinary officers to cull infected animals. Each farmer was also questioned about his livestock and management systems to determine any common practices, which would indicate any spread or transfer of the disease. Meat inspectors, who are always on hand to examine carcasses before sale to the public, were also trained to recognize TB nodules. If an infected animal was identified, samples were sent for testing.

To determine the prevalence of BTB in humans, samples were taken from people who did not respond to traditional TB therapy i.e. drugs used to treat pulmonary TB. In order to identify these patients, project staff used the leprosy and TB coordinators at district hospitals. Once samples were taken and BTB identified, patients were able to receive correct treatment. As with the farmers whose livestock were positively tested for BTB, questions were asked to determine factors which could indicate routes of transfer for the disease. The answers confirmed suspected causes: shared accommodation with livestock and consumption of unpasteurized milk or uncooked animal products.

Superior service

To get over the problem of samples being sent long distances from any market, abattoir or district hospital participating in the project, cold chain facilities were established. Districts without electricity were provided with kerosene freezers to store samples and a system established to allow for samples to be sent in cool boxes via public transport to the laboratories. However, to test samples of suspected BTB, diagnostic facilities had to be improved in order to allow for testing of potentially infectious material. Advice for re-designing existing facilities at the National Institute of Medical Research in Dar-es-Salaam was provided and staff trained in diagnostic testing and culture of mycobacteria. At the Department of Veterinary Medicine and Public Health at the Sokoine University of Agriculture, improvements in capability and available equipment have allowed the Department to become the first laboratory with molecular capabilities in Tanzania and a leading centre on mycobacterium in the region.

During the course of tuberculin-testing and questionnaire surveys, public health information on zoonotic diseases was disseminated informally to community leaders and householders. Annual progress meetings during the course of the project have enabled more people, including communities, to become involved and to be aware of the importance of zoonotic diseases in the region. With the facilities that now exist, and the improved collaboration of vets and medical researchers, it is hoped that sustained efforts to reduce the impact of other zoonotic diseases, such as rabies and brucellosis, can also be addressed.

Note: This DFID-funded Animal Health Project was led by the Moredun Research Institute in the UK in collaboration with the Department of Veterinary Medicine and Public Health, Sokoine University of Agriculture and the National Institute of Medical Research in Dar-es-Salaam

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