A one-tube nested polymerase chain reaction (PCR) method for the diagnosis of paucibacillary leprosy was developed using the repetitive RLEP sequence as a target. Detection of the PCR products was simplified by the adaptation of a colorimetric method. The test was specific for Mycobacterium leprae, and the sensitivity of the assay was 1 fg of purified genomic M. leprae DNA (less than one genome). Complete concordance was seen between the development of color and resolution on agarose gels. The results of frozen skin sections from untreated patients showed that the assay could detect 100% of multibacillary samples [bacterial index (BI) of 2 or more] and 69% and 70% of the samples with Bis of 1 and 0, respectively. The use of one-tube nested PCR in assessing the effectiveness of multidrug therapy (MDT) in leprosy also was determined. The simplified colorimetric assay was found to be sensitive, rapid and specific, and is suitable for use in routing diagnostic laboratories.
