Dosage and site of entry influence growth and dissemination of Mycobacterium leprae in T900r mice

The role of dosage of Mycobacterium leprae and the environment of the inoculated site, in producing leprosy lesions in immunologically-suppressed, highly-susceptible T900r mice, was investigated. Various doses of M. leprae, i.e., 10⁷, 10⁶, 10⁵, 10⁴, were inoculated into both flanks and footpads of two different groups of mice. The sites of inoculation were biopsied for histopathological examination and for M. leprae counts at the end of 6, 8 and 12 months. M. leprae multiplied at the infected site and disseminated to other parts of the body at all concentrations in the mice that were infected in the footpad with a temperature of 31°C. In animals inoculated at the flanks with a temperature of 37°C, multiplication was recorded only when the dosage of M. leprae was high and there was no dissemination of the organism in any of them. The temperature at the site of entry and the dose of infecting M. leprae may play an important role in the development of leprosy in susceptible individuals exposed to M. leprae.