Host-parasite relationships in experimental airborne tuberculosis. VI. Influence of vaccination with Bacille Calmette-Guérin on the onset and/or extent of hematogenous dissemination of virulent Mycobacterium tuberculosis to the lungs.

Guinea pigs vaccinated with bacille Calmette-Guérin (BCG) and unvaccinated guinea pigs were challenged by the respiratory route six weeks or six months after vaccination and sacrificed at various intervals after challenge. The six lobes of the lung were cultured separately, and the percentage of culture-positive lobes was calculated, as well as the log10 number of virulent bacilli recovered. The latter was subjected to an analysis of variance, which compared the fate of bacilli in the four largest lobes with the fate of those in the two smallest lobes. The results indicated no difference between the six-week and six-month intervals between vaccination and challenge. In the longer intervals between challenge and sacrifice, small numbers of secondary lesions could be seen on the lobes of the BCG-vaccinated animals. It was concluded that vaccination with BCG retarded the onset and/or reduced the extent of hematogenous dissemination of virulent mycobacteria to the lungs.