Novo marcador molecular para detecção e quantificação de Mycobacterium leprae por meio de PCR em tempo real

Abstract

Leprosy epidemiologic studies have been restricted to Mycobacterium leprae DNA detection in nasal and bucal swabs with scarce literature on the peripheral blood, probably due to the difficulty in finding bacilli in this type of sample. We present the first molecular epidemiology study using real time PCR (qPCR) for M. leprae detection and quantification on peripheral blood of 200 leprosy patients and 826 household contacts, associating them with others clinical and laboratorial parameters. The TaqMan® qPCR system was performed with two groups of primers and probes, aiming the following M. leprae genomic regions: 85B antigen and ML0024. The marker 85B presented a low specificity, probably due to the unspecific DNA amplification from other microorganisms, while the new marker ML0024 described in this study, was 100% M. leprae specific, with a positivity of 22% in leprosy patients, but variable in the different clinical forms, and with significant increase in the bacillary load of lepromatous leprosy patients blood in relation to the tuberculoid form. The detection in household contacts was 1.2%. The presence of M. leprae DNA in the blood of contacts that developed leprosy presented an odds ratio of 17.22-fold higher in favor of the disease occurrence in relation to the healthy contacts. The present study describes the ML0024 as the most sensitive and specific marker for M. leprae DNA detection, and it is the largest molecular epidemiologic study in the peripheral blood of leprosy patients and their contacts, with profound implications on the disease management. The M. leprae detection on the blood of contacts has imposed an alert for the possible bacilli transmission through the blood and the probability of these healthy carriers in transmitting the bacilli to populations of regions where leprosy has been eliminated.