Approaches to studying the transmission of Mycobacterium leprae.

A collaborative study has been undertaken to establish the relationship between infection by Mycobacterium leprae and the development of immunity in a community in which multidrug therapy (MDT) has been used for more than 10 years, to elucidate the pathogenesis of infection in leprosy, and to develop and test an intervention strategy based on chemotherapy for interruption of transmission of the organism in the community. The first phase of the study included the establishment of laboratory facilities and pilot work in India. In the course of the second phase, the entire populations of three villages in India and one in Ethiopia have been surveyed, nasal swabs were obtained for detection of M. leprae DNA by means of the polymerase chain reaction (PCR), specimens of saliva were obtained for measurement of levels of anti-M. leprae IgA antibodies, and follow-up surveys have been carried out. A double-blind trial of chemotherapy among subjects whose PCR was positive is proposed, to determine if the course of the infection can be influenced by treatment. The performance of large numbers of PCR tests in endemic countries has required the development of rigorous internal and external quality control procedures. These have shown that many batches (as many as 50%) fail to meet quality control criteria, and must be retested. Despite this, development of these methods, and their application to field studies should provide tools for studying the transmission of M. leprae, and direct methods of testing innovative interventions.