Therapeutic efficacy of artemether-lumefantrine and molecular markers of antimalarial drug resistance in Benin, 2022

From June to December 2022, a therapeutic efficacy study of Benin's first-line antimalarial, artemether-lumefantrine (AL), was conducted in three sites (Allada, Bohicon, and Parakou) to evaluate its therapeutic efficacy. Children aged 6-59 months with uncomplicated malaria were treated with AL and followed for 28 days to assess their clinical and parasitological response to treatment. Genotyping at three markers (msp1, msp2 and the PolyA microsatellite) and match counting using the WHO three-out-of-three algorithm were used to distinguish recrudescences from new infections. A two-out-of-three algorithm was also utilized as a sensitivity analysis. PCR uncorrected and corrected efficacy results at day 28 were calculated. Within the 28-day follow up period, there were 6 early treatment failures: 2 in Allada and 4 in Parakou. There were 15 late treatment failures: 3 in Allada, 4 in Bohicon, and 8 in Parakou, yielding uncorrected Kaplan-Meier treatment efficacies of 95.6% (95% CI 92-99), 94.0% (95% CI 88-100), and 89.6% (95% CI 84-95), respectively. After PCR correction, day 28 Kaplan-Meier efficacy was 97.4% (95% CI 96-100%)] in Allada, 98.5% (95% CI 96-100%) in Bohicon, and 94.8% (95% CI 91-99%)] in Parakou. Low day 3 slide positivity in Allada (1%), Bohicon (3%), and Parakou (2%) suggest no evidence of artemisinin resistance. Thirty paired (15 pairs of day zero and day of failure) samples from patients who failed treatment and 284 individual samples from non-failure patients without recurrent parasitemia were sequenced individually. No validated or candidate Pfk13 mutations associated with artemisinin resistance were detected. While the Pfdhps K540E mutation-a key marker of high-level sulfadoxine-pyrimethamine (SP) resistance-was also absent, other polymorphisms such as the Pfmdr1 Y184F and Pfdhps A437G mutations were common (ranging from 94% in Parakou to 100% in Allada). While Pfmdr1 Y184F may reflect selection under AL pressure, the high prevalence of Pfdhps A437G mutations likely reflects historical and ongoing SP exposure. Overall, AL demonstrated high therapeutic efficacy across all three sites in Benin at the time of evaluation.