Résumé
Urban settings often present low densities of mosquito vectors which do not allow to accurately assess the risk of arthropod-borne diseases based on entomological parameters. This study aims to evaluate the spatial risk of both malaria and arbovirus transmission in a northern urban area of Senegal, West-Africa, using antibody-based biomarkers of human exposure to Anopheles and Aedes mosquito bites. A cross-sectional study was undertaken between August and September 2014 (rainy season) in four urban districts (UDs) of the city of Saint-Louis, Senegal: Leona (LEO), Ndioloffene (NDI), Guet Ndar (GND) and Pi kine Sor Diagne (PSD). In each UD, dry blood spots were performed in 809 children aged 6-59 months and ELISA method was used to evaluate lgG antibody (Ab) responses to both gSG6-P1 (Anopheles) and Nterm-34kDa (Aedes) peptides of respective mosquito saliva. The median of lgG response levels to both gSG6-P1 and Nterm-34kDa salivary peptide varied significantly according to UDs and were lower in LEO compared to PSD, GND and NDI (p<0.0001 ). Heat maps of lgG responses to both salivary peptides indicated variations in the spatial distribution of the intensity of Ab responses inside UDs. There were no hot spots of malaria transmission risk (areas with children presenting a high lgG intensity) in LEO. Hot spots of malaria were mainly located in the northern part of NDI and GND, and in the southern part of PSD. As for the risk of arbovirus transmission, there were no hot spots in LEO and PSD. Hot spots of arbovirus transmission risk were located in some patch in the north of NDI and were dispersed throughout the UD of GND. Our results demonstrate that hot spots of both malaria and arbovirus transmission risk actually exist in northern parts of NDI and GND. This highlights that a targeted fight against mosquitoes in these hot spots could be effective against all mosquito-borne diseases. Antibody-based biomarkers could then help national control programs to target and prioritize vector control strategies in areas with common risk of malaria and arbovirus transmission.