LEPROSY AND TUBERCULOSIS - THE EPIDEMIOLOGIC CONSEQUENCES OF CROSS-IMMUNITY

Objectives. This study tested the hypothesis, first proposed by Chauss inand, that individual-level immunity acquired from exposure to tuberc ulosis may have contributed to the disappearance of leprosy from weste rn Europe. Methods. The epidemiological consequences of cross-immunity were assessed by the formulation of a mathematical model of the trans mission dynamics of tuberculosis and leprosy. Results. The conditions under which Mycobacterium tuberculosis could have eradicated Mycobacte rium um leprae were derived in terms of the basic reproductive fates o f the two infections and the degree of cross-immunity. Conclusions. If the degree of cross-immunity between two diseases within an individua l is known, then the epidemiological consequences of this cross-immuni ty can be assessed with transmission modeling. The results of this ana lysis, in combination with previous estimates of the basic reproductiv e rate of tuberculosis and degree of cross-immunity, imply that tuberc ulosis could have contributed to the decline of leprosy if the basic r eproductive rate of leprosy was low.