The predominate portals of entry or exit of M. leprae are still unclear. Recent studies emphasizing nasal carriage and mucosal immunity reflect interesting hypotheses but are not (yet?) convincing in themselves. If the presence of M. leprae in nasal cavities reflects transient carriage (the nose acting as an air filter), the data could also be consistent with skin as a portal of entry. Large, carefully conducted, long term studies will be required to solve this issue.
Does chemotherapy reduce transmission?
Though it is logical to infer that effective chemotherapy must reduce the risk of infection with M. leprae, and consequent incidence of leprosy disease, at least to some extent, it is extremely difficult to demonstrate such an effect convincingly. Leprosy incidence, is obviously strongly influenced by environmental or behavioral correlates of socio-economic development. Given that individuals may be infectious for long periods prior to diagnosis and treatment, the effect of even a good treatment program on the overall leprosy incidence may be small. The issue of MDT's impact on leprosy incidence, though of obvious political importance, may well be beyond the reach of convincing epidemiological evidence.
Vaccines in leprosy
The variability of BCG's efficacy between populations remains unexplained. The fact that BCG's effect in tuberculosis shows analogous variability enhances the importance of this issue for public health impact, and hence for research. The efficacy of BCG appears to decline with time. There are no data on whether BCG has any influence greater than 20 years after administration, either against leprosy or against tuberculosis. Since BCG has been given at birth in most countries for the past 20-30 years, it is now possible to study the influence of BCG in infancy on adult disease incidence. The evidence from Venezuela, Malawi and Burma that repeated BCG enhances its protective effect against leprosy increases the potential importance of such studies. The ongoing trial of a second dose of BCG among school children in Brazil will provide important data on this very practical intervention.
Research into the immunology of leprosy and into leprosy vaccines should be linked to the major international research effort devoted to tuberculosis. Comparisons between the two infections/diseases will provide useful insights. Leprosy should be included as an outcome in any future trial of a tuberculosis vaccine. The current interest in post-exposure vaccines against tuberculosis could also have implications for potential leprosy interventions either in high risk populations or in therapeutic context.
Participants：
Paul Fine, Chair, R. Truman. Rapporteur, G. Bjune, K. V. Desikan, A. Diallo, V.K. Edward, M.D. Gupte, J.D. Habbema, S. Izumi, C.K. Job, C.M. Martelli, A. Meima, R. G. Reddy.
P. Fine, London School of Hygiene & Tropical Medicine, London, U.K.
