Efficacy of Mycobacterium bovis BCG vaccination in mice undergoing prior pulmonary infection with atypical mycobacteria.

The efficacy of Mycobacterium bovis BCG immunization in mice with established pulmonary infections caused by atypical mycobacteria was studied. In all four strains of Mycobacterium tested (M. kansasii, M. simiae, M. avium, and M. scrofulaceum), intravenous inoculation with 10(6) BCG had no discernible effect upon the course of atypical mycobacterial infection within the lungs; despite this, however, all BCG-vaccinated groups of mice were fully resistant to a subsequent acute aerogenic challenge with M. tuberculosis H37Rv, regardless of the presence of the pulmonary atypical mycobacterial infections. Furthermore, animals infected with M. kansasii, M. simiae, or M. avium but not vaccinated with BCG expressed considerable antituberculous resistance within the lungs, resulting in significant prolonged survival of these animals. The relevance of these findings to the expression of antituberculous resistance in human populations in areas in which atypical mycobacteria are endemic and the failure of these findings to support the hypothesis that prior contact with atypical mycobacteria might in some way jeopardize or interfere with the efficacy of subsequent BCG vaccination are discussed.