Bacteriological follow-up of a primary molecular dapsone-resistant Mycobacterium leprae at CNDL, Niamey, Niger

Abstract Despite the proven efficacy multidrug therapy (MDT), drug resistance continues to be reported globally. In Niger, the historical period of long-term dapsone monotherapy may explain the emergence and persistence of these resistant strains, challenging the success of leprosy control programs. To address this challenge, this study focuses a long-term bacteriological monitoring. Specially, we report a case of a primary molecular dapsone-resistant strain identified at the Centre National Dermato-Lèpre (CNDL) in Niamey, the national center for leprosy. A two-year surveillance study screened 24 patients with multibacillary (MB) leprosy presenting a bacteriological index (BI) ≥ 2+. Genetic resistance mutations in rpoB , folP1 , and gyrA genes (conferring resistance to rifampicin, dapsone, and fluoroquinolones, respectively) were investigated using multiplex PCR followed by the GenoType LepraeDR test. One patient with primary molecular resistance to dapsone representing a prevalence of 4.16% within the cohort was identified and monitored during a 12-month MDT regimen. Bacteriological follow-up evaluated both the BI and the morphological index (MI) at baseline and at the end of treatment. Following 12 months of MDT, the patient showed a decrease of 1.33 points in the BI. The MI dropped drastically from 69% to 1%, indicating near-complete clearing of viable bacilli. These results confirm the therapeutic efficacy of standard MDT against dapsone-resistance Mycobacterium leprae strains. However, the residual 1% MI suggests the persistence of viable mutated bacilli. Strict, long-term monitoring of this patient remains crucial to prevent clinical relapse and contain the transmission of drug-resistant leprosy in Niger.