In many industrially developed countries cases of human tuberculosis due to M. bovis appeared to be due to reactivation of infection acquired before the completion of bovine tuberculosis eradication programmes. It seemed likely that this form of human tuberculosis would become increasingly rare. With the advent of the human immunodeficiency virus (HIV) pandemic, however, it seemed that this trend could be reversing. Although many questions remain, it appears that M. bovisis less virulent than <i>M. tuberculosis </i> in humans; if apparent differences in virulence are the result of differing susceptibility to the host defence mechanisms, the immunosuppression induced by HIV infection could well annul these differences.
In view of the possibility of a major health problem worldwide, more epidemiological information was urgently sought on the incidence and distribution of infection and disease due to M. bovis in the human and animal population. Early results demonstrated three worrying features of HIV-related tuberculosis due to M. bovis: human-to-human transmission leading to overt disease definitely occurs; the interval between infection and overt disease is short; and multi-drug resistant disease may be generated and disseminated. Such reports raise serious implications for global control of tuberculosis, particularly for communities economically dependent upon cattle and in frequent close contact with them.
For these reasons, more information on the occurrence and distribution of tuberculosis in cattle and other animals worldwide, and on the occurrence, extent and mode of interspecies transmission of disease in pastoralist communities with a high prevalence of HIV infection, is needed. Accumulation of data would, however, be valueless unless it led to practical control measures. A better understanding of the epidemiology of M. bovis infection and disease in developing countries could lead to the design and adoption of area-specific public health measures. The eradication of cattle tuberculosis, so successful in several developed countries, by the test and slaughter policy would be prohibitively expensive in most developing nations (and prevented by religious beliefs in countries such as India). Thus, protection of cattle and other farm animals by vaccination would be an appropriate alternative. This approach fell into general disfavour following the apparent failure of a large BCG vaccination trial of cattle in Malawi, and because such vaccination leads to tuberculin conversion, compromising the key diagnostic skin test. Nevertheless, the advent of more effective vaccines could lead to a radically new approach to this additional threat to human health.
Cosivi, O.; Daborn, C.; Grange, J.M. HIV-related tuberculosis due to IMycobacterium bovisI. European Respiratory Journal (1994) 7 (9) 1564-1566. [DOI: 10.1183/09031936.94.07091564]