Experimental murine leprosy: growth of Mycobacterium lepraemurium in C3H and C57/BL mice after footpad inoculation.

Forty-three female C57/BL and C3H mice were inoculated with 2.7 X 10(6) Mycobacterium lepraemurium into each hind footpad. The foot thickness and the number of acid-fast bacilli in the footpad and popliteal and inquinal lymph nodes were recorded. In addition the morphological index and the mean bacillary length were determined in the footpad and in the popliteal lymph node. The bacilli multiplied in both strains during the first 4 weeks after inoculation. After that time no further increase in acid-fast bacilli was observed in the C57/BL strain; the bacilli became elongated and the morphological index decreased. These changes were preceded by a local swelling of the footpad due to the onset of an immune reaction. Thus, under the present conditions, C57/BL mice were able to resist experimental infection with M. lepraemurium by developing an immune response. In C3H mice no indication of an immune reaction was detected, and the bacilli continued to multiply throughout the observation period. The mouse footpad model seems to provide an excellent basis for the use of experimental murine leprosy to study immunity to mycobacterial infections. Certain aspects of the present model are discussed in relation to the mouse footpad model as used in the study of M. leprae infection in mice.