Dynamics and Characterization of Larval Breeding Sites of Anopheles gambiae s.l. in the Department of Saint-Louis (Senegal)

Malaria remains a major public health problem in Senegal, particularly in areas in the pre-elimination phase, such as the department of Saint-Louis, where the incidence of cases has increased sharply between 2021 and 2024. This study aimed to characterize the larval breeding sites of Anopheles gambiae complex the main vectors of malaria, and to identify the species present. Surveys were carried out during the 2024 rainy season in five municipalities of the department. Each deposit was described, georeferenced and subjected to physicochemical measurements (pH, temperature, salinity, conductivity). Larval density was estimated by the dipping method. Out of 143 gîtes visited, 100 were positive for anopheles’ larvae, of which 59% were natural and 41% were artificial. Breeding sites smaller than 10 m² concentrated 82.3% of the larvae (p < 0.001). Mapping showed high activity in the middle of the rainy season, particularly in Cité Niakh (Saint-Louis), Ngallèle (Saint-Louis), Pikine (Saint-Louis) and Diougop (Gandon), with a decrease at the end of the rainy season. PCR identification showed that the majority consisted of Anopheles arabiensis (95%), followed by An. melas (4%) and An. gambiae s.s. (1%). The physicochemical parameters of the deposits had averages of pH 8.12 ± 0.55, temperature 31.6°C ± 4.28, salinity 4.38 g/L ± 3.21 and conductivity 8,135 μS/cm ± 5,990. In conclusion, these results highlight the complexity of the ecological factors influencing the presence of mosquito vectors and emphasize the need to strengthen entomological surveillance and implement targeted actions to limit malaria