Some aspects of the pathogenesis and pathomorphology of leprosy

The results of bacteriological and histological examinations of the organs of mice infected in the footpad with human leprosy bacilli by the Shepard method are summarized. The periods of observation ranged from a few days to 2 years. The disease developed in mice as a chronic infection with a lengthy "incubation" period of 3-4 months or more without symptoms. Usually about 2 years after inoculation, or in some cases after a shorter interval, the disease became generalized. Different types of tissue reaction occurred: simple inflammatory infiltration, tuberculoid granuloma, and leproma-like granuloma, similar to the clinical types of leprosy in man. When the infection became general, cells resembling lepra cells formed in the internal organs and at the site of infection. These cells contained massive intracellular aggregations of mycobacteria and compact globi with lipids and a vacuolized protoplasm, similar in origin and morphology to the lepra cells in human lesions. Changes were found in the neuroreceptor apparatus of the skin of the mice, with groups of leprosy bacilli in the endoneurium, the Schwann cells, and the perineural spaces. The length of the experiments and the histological examination of material from the sacrificed mice at different stages of the infective process revealed biological parallels with human leprosy and threw light on a number of aspects of the pathogenesis of leprosy.