Some Aspects of the Epidemiology of Leprosy

Soon after Hansen's discovery of M. leprae and Koch's discovery of M. tuberculosis a relationship between the two diseases was considered. In 1924, Sir Leonard Rogers (19) , in a Croonian Lecture on lepros1 researches, stated: "It is now well established that native races in Central Africa, Oceania and America, among whom some of the highest leprosy rates are found, have very low percentages of positive tuberculin reactions." This statement . was illustrated by a table showing leprosy rates and percentages of positive reactions to tuberculin (von Pirquet). Rogers concluded that mild tuberculosis may give some protection against leprosy and that tuberculosis might be one factor in the extinction of leprosy in Europe. Very little attention has been paid to this remarkable observation. BCG vaccination was tried as a treatment for leprosy, but interest rapidly disappeared after it seemed evident that BCG vaccination was ineffective and that it might provoke leprosy reactions. In 1941 the hypothesis of an antagonism between leprosy and tuberculosis was revived by Chaussinand (~. 5). His evidence, although mainly circumstantial, has stimulated other workers to further studies on the subject. In the next twenty years many papers on the immunologic relationship between the two diseases were published. It was shown that the prevalence of positive lepromin reactors is higher in tuberculin-positive than in tuberculin-negative individuals and that a very high percentage of negative lepromin reactions can be converted into positive by BCG vaccination. This suggests an increase of resistance to M. leprae by tuberculosis infection or by BCG vaccination. Other investigators, however, failed to