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1. Introduction
Malaria is a vector-borne disease, which requires three essential factors for its existence and transmission: Plasmodium parasites, mosquito vectors, and human hosts [1,2]. There are three specific species of Plasmodium affecting humans, which are Plasmodium falciparum (the most common and lethal parasite species in sub-Saharan Africa), Plasmodium vivax, and Plasmodium ovale, the common species to humans and gorillas. Plasmodium knowlesi, like Plasmodium malariae, generally affects primates and gorillas, with some examples of transmission to humans in Malaysia [3]. The two major parasites are P. falciparum in the Tropics and P. vivax in more temperate regions. There are various species of anopheles vectors which are competent for malaria transmission. The main malaria vectors in Africa and Senegal are Anopheles gambiae, Anopheles funestus, Anopheles arabiensis, and Anopheles melas to a lesser extent [4,5,6]. Beyond these essential factors, malaria transmission risk can be sustained or strengthened by specific environmental and climatic conditions as well as a large range of socio-economic factors for the African countries [7,8].
In particular, the influence of climate variability on health is widely recognized [9,10]. The economic development in Africa is severely affected by a human and animal disease burden [11,12]. During the 1970s and 1980s, rainfall decreased by nearly 30% over the Sahel, with severe droughts occurring in 1972, 1983, and 1991-1992 [13,14,15,16,17]. Some studies have highlighted how the drought during the 1970s and 1980s reduced the distribution and abundance of mosquito vectors without leading to drastic malaria transmission [18]. Increasing drug resistance in children and pregnant women populations with altered immunity illustrates this finding about high malaria occurrence despite reduced rainfall in the Sahel [19]. Regarding the relationship between rainfall and malaria, some studies [20,21,22] have investigated the malaria decrease and drought in the Niayes (a northwestern area in Senegal) and the Sahel in general. The main malaria vector, An. funestus, in these regions has almost disappeared following the drought in the 1970s and 1980s [17]. The abundance of other anopheles species also decreased significantly over the region, compared to An. arabiensis, which is another efficient malaria vector due to its zoophilic characteristics in rural areas [23,24,25,26,27]. Thus, the observed decline of malaria is related to the disappearance of An. funestus and declining population of An. gambiae, which can be...