Malaria transmission dynamics, vector diversity, and insecticide resistance profiles in two health districts of southern Benin.

BACKGROUND

Malaria transmission in Benin is heterogeneous, influenced by ecological settings and environmental changes affecting Plasmodium spp. prevalence, vector species composition, and insecticide resistance. Comprehensive local data on transmission dynamics remain limited, particularly in southern Benin. This study assessed malaria transmission, vector diversity, and insecticide resistance in two health districts to support the National Malaria Control Programme in designing targeted and effective vector control strategies.

METHODS

A repeated cross-sectional study was conducted in two health districts in southern Benin (Ouidah-Kpomasse-Tori Bossito (OKT) and Adjohoun-Bonou-Dangbo (ABD) districts). In OKT, blood samples were collected from August 2021 to August 2022, while in ABD sampling was conducted from July to November 2024. Human participants were screened for Plasmodium infections using microscopy and rapid diagnostic tests. Adult Anopheles mosquitoes were collected in both districts during rainy and dry seasons using human landing catches. Mosquitoes were morphologically and molecularly identified and screened for Plasmodium spp. Insecticide resistance was assessed through detection of kdr (L1014F) and ace-1 (G119S) mutations, and bioassays with pyrethroids (alpha-cypermethrin and deltamethrin) and synergists (PBO).

RESULTS

A total of 1,962 participants were enrolled (OKT 1,577; ABD 385). Overall Plasmodium prevalence was 28.2% in OKT and 21.0% in ABD, with higher prevalence during the rainy season compared to the dry season in OKT (37.0% vs. 20.9%, p < 0.0001). Anopheles gambiae s.l. was the predominant species complex, with seasonal shifts in species composition determined molecularly; An. gambiae s.s. dominating in the rainy season (80.0% in OKT, 54% in ABD), while An. coluzzii predominated in the dry season (92.5% in OKT, 98.3% in ABD). High frequencies of kdr L1014F mutations were detected (0.62-0.93), whereas ace-1 resistance remained low (≤0.13). Plasmodium infection in mosquitoes was rare (<2%), and blood meals showed strong anthropophagy (97.8%). PBO bioassays indicated partial restoration of susceptibility to deltamethrin and alpha-cypermethrin.

CONCLUSIONS

Malaria transmission in southern Benin remains sustained by high seasonal prevalence in humans, intense human-vector contact, and widespread pyrethroid resistance in vectors. Seasonal and spatial heterogeneity in vector species composition and resistance profiles highlight the need for adaptive, locally tailored control strategies, including monitoring and management of insecticide resistance.

CLINICAL TRIAL REGISTRATION: Not applicable.