Zoonotic aspects of Mycobacterium bovis infection.

The bovine tuberculosis eradication campaigns in many industrially developed countries have led to a huge reduction in the incidence of human tuberculosis caused by Mycobacterium bovis. Overt disease in man may, however, manifest decades after the initial infection and the occurrence of such disease raises several important questions. In particular, it is important to determine whether man-to-man transmission occurs, thereby rendering man a continuing reservoir of infection, and whether, if this is the case, man develops infectious forms of tuberculosis that enable M. bovis to be transmitted back to cattle. Epidemiological studies in South East England indicate that human tuberculosis due to M. bovis is rare and that the incidence is declining. In contrast to earlier days, the lung is now involved in many cases, raising the possibility of transmission of bacilli to other human beings and to cattle by the aerogenous route. No direct evidence of man-to-man transmission of overt disease was found but it is possible that inapparent primary pulmonary infections are occurring and these may proceed to overt post-primary disease in the future. The genito-urinary tract is now the most prevalent site of non-pulmonary lesions and there is firm evidence that this form of tuberculosis poses a hazard to cattle. Though uncommon, human tuberculosis due to M. bovis is still a public health problem of concern to both the medical and veterinary professions and there is a need to maintain careful bacteriological surveillance.