Role of Anopheles funestus in sustaining residual malaria transmission in central Senegal

Abstract Background Anopheles funestus is one of the major malaria vectors in sub-Saharan Africa. In Senegal, it is found across nearly all biogeographical areas, often replacing An. gambiae s.l. and sustaining malaria transmission during the dry season. Despite its recognized role as a major vector, the specific contribution of An. funestus to malaria transmission in many malaria-endemic areas remains underexplored. This study aims to assess the contribution of An. funestus in malaria transmission in two health districts in Central Senegal. Methods Adult mosquitoes were collected from July 2018 to November 2019 in the health districts of Nioro (Ndramé Ndimb) and Ndoffane (Tawa Mboudaye) using Human Landing Catches (HLCs) and Pyrethrum Spray Catches (PSCs). Anopheline specimens were identified morphologically using standard dichotomous keys, with species confirmation performed by polymerase chain reaction (PCR). Plasmodium falciparum infection and blood meals sources were determined using Enzyme-Linked Immunosorbent Assay (ELISA) techniques. Results A total of 6,932 Anopheles mosquitoes were collected. Of these, 73.7% (5,108/6,932) were identified as An. funestus , which was the predominant species at both study sites, with 1,364 specimens collected in Nioro and 3,744 in Ndoffane. Molecular analysis confirmed that An. funestus sensu stricto (s.s) was the only member of the An. funestus group recorded. In Ndramé Ndimb, the mean human biting rate and indoor resting density were 2.8 bites per person per night (b/p/n) and 9.0 females per room (f/r), respectively, compared to 12.4 b/p/n and 19.1 f/r in Tawa Mboudaye. The P. falciparum circumsporozoite rate was 0.3% in both villages, resulting in estimated entomological inoculation rates (EIRs) of 0.008 and 0.038 infected bites per person per night in Ndramé Ndimb and Tawa Mboudaye, respectively. The human blood index was relatively low, with only 22.3% (324/1,452) of An. funestus specimens found to have fed on humans. Conclusions This study highlights the predominance of An. funestus and its important role in sustaining residual malaria transmission in central Senegal, even where overall transmission intensity remains low.