Molecular Assays Evaluated for Leprosy

The increased reliability and efficiency of quantitative polymerase chain reaction (qPCR) assays make them candidates for diagnosing leprosy.

The specificity and sensitivity of different qPCR assays for the chronic infectious disease caused by Mycobacterium leprae needs to be evaluated as a range of clinical samples could bias the molecular results.


Scientists at the Instituto Oswaldo Cruz (Rio de Janeiro, Brazil) used qPCR assays to amplify different M. leprae gene targets and compared them for leprosy differential diagnosis. The qPCR assays were performed on frozen skin biopsy samples from a total of 62 patients: 21 untreated multibacillary (MB), 26 untreated paucibacillary (PB) leprosy patients, as well as 10 patients suffering from other dermatological diseases and five healthy donors.

The four gene targets were superoxide dismutase (sodA), 16S ribosomal RNA (16S rRNA), the protective antigen Ag 85B and M. leprae repetitive elements (RLEP). The qPCRs were assayed using a 7000 real-time PCR system and fluorescent accumulation data for skin biopsies specimens were analyzed by the ABI PRISM 7000 Sequence Detection System software (Applied Biosystems, Carlsbad, CA, USA; www.appliedbiosystems.com). The scientists found a decreasing sensitivity for Ag 85B (66.1%), 16S rRNA (62.9%), and sodA (59.7%) optimized assay classifiers, but with similar maximum specificity for leprosy diagnosis. Conversely, the RLEP assay showed to be the most sensitive (87.1%). Moreover, RLEP assay was positive for three samples of patients originally not diagnosed as having leprosy, but these patients developed leprosy 5 to 10 years after the collection of the biopsy.

In addition, four other samples of patients clinically classified as non-leprosy presented detectable chromosome counts in their samples by the RLEP assay suggesting that those patients had either leprosy that was misdiagnosed or a subclinical state of leprosy. Overall, these results are encouraging and suggest that RLEP assay could be useful as a sensitive diagnostic test to detect M. leprae infection before major clinical manifestations. Leprosy still affects 211,903 individuals per year worldwide and lead to permanent nerve injury that is generally associated with late diagnosis. The study was published in October 2011 in the Public Library of Science Neglected Tropical Disease.

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Instituto Oswaldo Cruz
Applied Biosystems