Endemicity of a Yellow Fever Virus Strain Revealed by Entomological Surveillance in Southeastern Senegal.

Yellow fever virus is an endemic mosquito-borne flavivirus that continues to cause outbreaks in human populations in Senegal despite the availability of a vaccine. Entomological surveillance was implemented in southeastern Senegal for the early detection of sylvatic amplifications, which usually trigger human cases. Mosquito vectors were collected monthly using Prokopack aspirators and double-net traps. Mosquitoes were pooled and tested by quantitative reverse transcription polymerase chain reaction assay targeting antigens of common arboviruses circulating in the area, and then positive samples were subjected to whole genome sequencing using Illumina iSeq system. We identified a recently emerged yellow fever virus strain persisting within a sylvatic cycle and linked to human cases. Genomic analyses revealed genetic stability, underscoring endemicity and ongoing spillover risks. These findings emphasize the need for continuous surveillance and vaccination to prevent outbreaks in vulnerable populations.