Lack of a sustained protection against murine leprosy in C3H mice vaccinated with extracts of Mycobacterium lepraemurium in admixture with Mycobacterium bovis (BCG).

Inbred C3H mice were vaccinated intradermally with a single dose of live BCG, whole extracts of mechanically disrupted Mycobacterium lepraemurium (MLM), or a mixture of both these agents. Four weeks later, they were infected in one hind foot pad with freshly harvested MLM. Vaccination with BCG-containing preparations significantly reduced the multiplication of MLM in the infected foot pad and the bacillary dissemination to the draining popliteal lymph node and the spleen, while vaccination with MLM extracts solely limited the growth of MLM in the foot pad. MLM antigens in admixture with BCG did not offer a better protection than BCG alone. The protective effect was observed near the 15th week after the infection. At 30 weeks post-infection, no significant difference in bacillary counts was noted between the vaccinated and unvaccinated mice. In addition, the mean survival time of vaccinated mice did not significantly differ from that of control mice. Thus, in the C3H mouse, vaccination was able to limit temporarily the growth and dissemination of MLM, but these effects were unable to stop the fatal progression of murine leprosy.