Bovine variants of Mycobacterium tuberculosis isolated in Liverpool during the period 1969 to 1983: an epidemiological survey.

Between 1969 and 1983 inclusive, the bovine variants of Mycobacterium tuberculosis (M. bovis and M. africanum) were isolated from 75 patients with tuberculosis. This represented 2.9 per cent of all significant mycobacteria identified at the Liverpool Public Health Laboratory during this period. The clinical and radiological features of infection did not differ from those found with M. tuberculosis. There was an association between M. bovis infection, extrapulmonary disease and lifelong United Kingdom residency, and between M. africanum infection, pulmonary disease and immigrant status. Correlations between the present incidence of reactivated M. bovis disease and past prevalence of bovine tuberculosis in man and cattle, and between the isolation rate of M. africanum and the size of the immigrant community served by the laboratory, were also demonstrated. All the patients with M. bovis infection were considered to have a reactivated or slowly progressive primary infection. It is proposed that M. bovis only accounts for a small proportion of isolates from adults with tuberculosis because the organism displays a low tendency to reactivate.