Plasmodium falciparum sporozoite loads in Anopheles gambiae s.l. across agro-ecological zones of Benin: a cross-sectional field study

Malaria transmission depends critically on the vectorial competence of Anopheles mosquitoes, which is partly reflected by the quantity of infectious Plasmodium falciparum forms harboured in the salivary glands. Whether agro-ecological heterogeneity and vector species identity modulate this parasite burden remains poorly characterized in Benin. Anopheles gambiae s.l. were collected by Human Landing Catch across 12 localities spanning 7 agro-ecological zones in Benin during August–October 2022. Species were identified by SINE-PCR. P. falciparum infection was assessed by circumsporozoite protein (CSP) ELISA, and sporozoite load was quantified in positive head–thorax preparations by real-time PCR targeting the plasmepsin gene (NZYTech kit, ref. MD 02411). Statistical comparisons across agro-ecological zones (within each species) used the Kruskal–Wallis test, and the two-species comparison used the Mann–Whitney U test, in R v4.4.1. A total of 1,355 individuals were molecularly analyzed for species identification. Of 3,021 mosquitoes collected, these 1,355 yielded 858 An. coluzzii (63.32%), 489 An. gambiae (36.09%), and 8 An. arabiensis (0.59%). The overall sporozoite index was 5.98% (95% CI 4.8–7.4%), ranging from 0% in Cotonou and Parakou to 16.19% in Boukoumbé. No significant inter-zonal variation in sporozoite load was detected in either An. coluzzii (Kruskal–Wallis: H = 5.79, df = 3, p = 0.122) or An. gambiae ( H = 3.25, df = 2, p = 0.197). However, An. coluzzii carried a significantly higher sporozoite burden than An. gambiae (Mann–Whitney U = 381, p < 0.001). Broad agro-ecological zone categories were not associated with detectable differences in individual P. falciparum sporozoite load in the principal malaria vectors of Benin. Anopheles coluzzii carried a significantly higher sporozoite burden than An. gambiae , indicating species-level differences in parasite permissiveness that merit further investigation.