New prospects for the study of leprosy in the laboratory.

Although Mycobacterium leprae was identified earlier than Myco. tuberculosis, it has still not been cultured in vitro and only in 1960 was an infection obtained in laboratory animals. However, important advances have been made in the field of experimental leprosy in the last decade due to the development of new techniques and models for studying Myco. leprae in vivo, thus overcoming the limitations imposed by a non-cultivable mycobacterium. Quantitative techniques using Myco. lepraemurium provided the first model for developing an indirect method for distinguishing dead (non-infectious) from living (infectious) bacilli, based on morphological differences in organisms stained by the Ziehl-Neelsen method. However, the most important advances resulted from the limited and localized growth of Myco. leprae when inoculated into the foot pads of mice and, later, the more substantial and generalized multiplication of Myco. leprae in immunologically deficient mice (thymectomized and irradiated with a dose of 900 r). Moreover, in the immunologically deficient animals, the infection eventually resulted in a disease replicating that of lepromatous type leprosy in man, including the involvement of peripheral nerves.The results from these studies and the future prospects for the study of leprosy in the laboratory are reviewed in this article.