Differential contribution of Anopheles coustani and Anopheles arabiensis to the transmission of Plasmodium falciparum and Plasmodium vivax in two neighboring villages of Madagascar

Abstract

BackgroundMalaria is still a heavy public health concern in Madagascar. Few studies combining parasitology and entomology have been recently conducted despite the need for such information to design proper vector control measures. In a region of moderate to intense transmission of both Plasmodium falciparum and Plasmodium vivax, we conducted a combined parasitology and entomology survey in two nearby villages, across a malaria transmission season from December 2016 to April 2017.\n\nMethodology/Principal findingsCommunity-based surveys were conducted in the two close by villages at three time points during a single malaria transmission season. Plasmodium carriage in the human populations was determined by Rapid Diagnostic Tests (RDTs), microscopy and real-time PCR. Anthropophilic mosquitoes were captured by human landing captures and presence of Plasmodium sporozoites was assessed by robust Real Time PCR. Overall human malaria prevalence was 8.0% by RDT, 4.8% by microscopy and 11.9% by PCR, mainly due to P. falciparum detected in 92.2% of the PCR positive samples and Plasmodium vivax (5.7%). No significant differences in Plasmodium human carriage was observed between the 2 villages at any time point. Of the 1553 anopheline mosquitoes tested, 13 were found carrying Plasmodium sporozoites, the majority of them being captured outdoor. The mosquito sporozoite indices were not significantly different between the two villages. However, our entomological analysis revealed that Anopheles coustani was the main vector in one village, being responsible of 25.5 infective bites during the whole survey, whereas it was Anopheles arabiensis in the other village with 15 infective bites. In addition, we found a significant higher number of endophagic An. coustani and An. arabiensis in one village compared to the other.\n\nConclusions/SignificanceDespite similar human malaria prevalence in two close by villages, the entomological survey demonstrated the contribution of two different mosquito species in each village, and importantly the role of a suspected secondary malaria vector, An. coustani, as the main vector in one village. This, along with its higher endophagic rate in that village, highlights the importance of combining parasitology and entomology surveys for better targeting the actual local malaria vector. Such study should contribute to the malaria pre-elimination goal established under the 2018-2022 National Malaria Strategic Plan.\n\nAuthor SummaryMalaria is still a major health concern in many countries in sub-Saharan Africa such as Madagascar. In this study, we determined the contribution of malaria vectors in the transmission of Plasmodium parasites in two nearby villages in an area of moderate to high malaria transmission in Madagascar. We collected, during a single malaria transmission season, parasitological data in the human population and entomological data in the mosquito population, in order to evaluate Plasmodium carriage in these two populations. The results showed that despite similarity in human malaria prevalence and in vector species diversity in each village, the contribution of vectors was different between the two villages. An. arabiensis was the major vector in Ambohitromby while it was An. coustani that played this role in Miarinarivo. Importantly, this study is the first that clearly demonstrates that An. coustani could act as a major local vector in Madagascar. Such study should help deploying adapted malaria vector control and contributing to the malaria pre-elimination goal established under the 2018-2022 National Malaria Strategic Plan.