Challenging the notion of Aedes aegypti as the primary chikungunya virus vector: insights from Kédougou, Southeastern Senegal

Background: Chikungunya fever (CHIK) caused by the mosquito-borne chikungunya virus (CHIKV) and transmitted by Aedes (Ae.) mosquitoes, remains a public health burden throughout the tropics. During the CHIK outbreak in southeastern Senegal in August 2023, an entomologic investigation was conducted to identify the vector(s) and characterize the virus strains. Methods: Adult mosquitoes were collected indoors and outdoors from houses of confirmed CHIK cases and their immediate neighborhoods using Prokopack aspirators and double-net traps and all water containers were inspected for aquatic stages. Mosquito pools were tested for CHIKV by RT-qPCR and positive samples were subjected to whole genome sequencing using Illumina iSeq system. Results: Animal watering points, bricks, and tree holes were the most common sites for Ae. aegypti larvae and pupae. While immature Ae. aegypti were found in all affected villages, with Breteau and Container indices exceeding the WHO epidemic thresholds, Ae. furcifer emerged as the most abundant host-seeking species collected in domestic areas. CHIKV was detected in 31 mosquito pools, primarily in Ae. furcifer (22 pools) and only one pool of Ae. aegypti. Other Ae. species accounted for 8 positive pools and Anopheles (An.) gambiae complex, the primary malaria vector, one pool. Phylogenetic analysis confirmed the close relationship between 2023 CHIKV strains circulating in humans and mosquitoes, and those responsible for the 2015 outbreak. Conclusions: Our study highlights the urgent need to include sylvatic mosquitoes in surveillance and control programs that until now have mainly focused on Ae. aegypti. Moreover, the potential role of An. gambiae in the CHIKV transmission in Senegal warrants further investigation.