Residual malaria transmission in central-western Senegal: role and bionomics of the local populations of Anopheles arabiensis and Anopheles melas

Abstract

Abstract Background Understanding the behavior and ecology of local malaria vectors is essential for the effectiveness of the commonly used vector-targeted malaria control tools in areas of low malaria transmission. This study was conducted to determine species composition, biting behavior and infectivity of the major Anophelesvectors of Plasmodium falciparum in low transmission settings in central western Senegal. Methods Adult mosquitoes were collected using human landing catches (HLCs) during two consecutive nights and Pyrethrum Spray Catches (PSCs) in 30 to 40 randomly selected rooms, from July 2017 to December 2018 in three villages. Anopheline mosquitoes were morphologically identified using conventional keys; their reproductive status assessed by ovary dissections, and a sub-sample of An. gambiae s.l. were identified to species level using polymerase chain reaction (PCR). Plasmodium sporozoite infections were detected using real-time quantitative PCR (qPCR). Results During this study 3684 Anopheles were collected of which 97% were An. gambiae s.l., 0.6% were Anopheles funestus and 2.4% were Anopheles pharoensis. Molecular identification of 1877 An. gambiae s.l. revealed a predominance of An. arabiensis (68.7%), followed by An. melas (28.8%) and An. coluzzii (2.1%). The overall human biting rate of An. gambiae s.l. was highest in the inland site of Keur Martin with 4.92 bites per person per night, while it was similar in the deltaic site, Diofior (0.51) and the coastal site, Mbine Coly (0.67). Parity rates were similar in An. arabiensis (45%) and An. melas (42%). Sporozoite infections were detected in both An. arabiensis and An. melas with the respective infection rates of 1.39% (N=8) and 0.41% (N=1). Conclusion Results suggest that low residual malaria in central western Senegal is transmitted by An. arabiensis and An. melas. Consequently, both vectors will need to be targeted as part of malaria elimination efforts in this area of Senegal.