Application of polymerase chain reaction for the detection of Mycobacterium leprae DNA in specimens from treated leprosy patients.

In this study of leprosy patients apparently cured by dapsone monotherapy, the polymerase chain reaction (PCR), one of the most reliable and sensitive DNA-based assays, was used for the specific detection of Mycobacterium leprae DNA. Sputum and slit-skin samples from 44 such patients at Baba Baghi Leprosy Sanatorium in Iran were examined. Primers for a 530-base-pair fragment of the gene encoding the 36-kDa antigen of M. leprae were used for the study. The PCR results were compared with microscopy for acid-fast bacilli. Of the 44 sputum samples, 2 were positive by PCR (4.5%) and of the 44 slit-skin swabs taken from the same patients, 10 were PCR positive (22.7%). Only one patient was PCR positive for both sputum and slit-skin specimens (2.3%). No positive results were found by acid-fast microscopy. In total, 11 of 44 (25%) patients in this study were found to be PCR positive for M. leprae, and it was thought probable that this indicated the presence of live organisms. Particularly interesting was the statistically significant association of positive results from slit-skin swabs with paucibacillary rather than multibacillary leprosy. It is suggested that whereas relapse or immunological reaction in paucibacillary disease may result from surviving organisms, in multibacillary leprosy this may be due to re-infection.