Host-parasite relationships in experimental airborne tuberculosis. VII. Fate of Mycobacterium tuberculosis in primary lung lesions and in primary lesion-free lung tissue infected as a result of bacillemia.

Evidence suggests that in humans tuberculous disease usually arises at apical or subapical sites in the lungs seeded as a consequence of an early bacillemic phase of the infection. This study examined the fate of bacilli transported via the bloodstream to metastatic sites in the lungs of guinea pigs after aerosol infection with approximately two viable virulent Mycobacterium tuberculosis. The results revealed that, even after logarithmic-phase multiplication of bacilli in primary lesions had been terminated, bacilli seeded via the bloodstream to metastatic sites in the lung were able to multiply. These observations, made in an animal model that mimics the conditions under which tuberculosis develops in human subjects, challenge the relevance of systemic macrophage activation in experimental airborne tuberculosis in guinea pigs.