Immunotherapy and immunoprophylaxis in leprosy

Abstract

The results reported demonstrate the efficacy of a mixture of BCG and M. leprae in inducing favorable immunological changes in low resistance forms of leprosy and in susceptible, possibly infected Mitsuda-negative contacts. The strategy to be employed in immunoprophylaxis would reserve the vaccine precisely for this limited high-risk population. The author proposes the following. To limit the application of the vaccine to epidemiologically-defined contacts. Studies in Venezuela have established an average number of 50 contacts for each case of active leprosy: To detect the susceptible persons within this group of contacts by means of a skin test with soluble antigen of M. leprae (SPA). The group of negative reactors defines those individuals who are the greatest risk of acquiring the disease, especially in multibacillary form. These criteria would substantially reduce the group to be vaccinated, so that attention could be focussed on the population of susceptible individuals. Thus a large-scale field study would be evaluated in terms of the difference in the incidence of new cases between the two relevant groups - vaccinated SPA negative contacts and unvaccinated negative contacts. The author considers the following conditions indispensable for the realization and evaluation of a field trial to determine the efficacy of preventive vaccination in leprosy: the selection of an area of high prevalence; definition of population groups at high risk within the area by epidemiological criteria (contacts); further identification of the susceptible population by means of immunological criteria (skin tests); and the availability of an adequate public health infrastructure in the area.