Entomological response to control interventions during the first chikungunya and dengue outbreak in White Nile, Sudan

White Nile State in south-central Sudan experienced its first documented outbreak of dengue and chikungunya in 2022. The present study evaluates the entomological response following an integrated vector management package implemented during the outbreak in Tandalti town.

Longitudinal entomological surveillance across 10 clusters encompassing 600 households and 2500 containers was conducted from July to December 2022. Stegomyia indices together with per-container productivity of larvae and pupae were calculated to quantify container infestation and evaluate entomological changes following the intervention.

Widespread Aedes aegypti infestation was documented across all clusters, with clay pots (zeers) and barrels accounting for 97.1% of positive containers. Following the implementation of control interventions, Stegomyia indices decreased substantially from September to December (house index by 78.2%, container index by 35.1%, Breteau index by 92.8% and pupal/demographic index by 94.1%) and total immatures decreased by 89.5% (larvae) and 95.5% (pupae). The few residual containers remaining in December were still producing pupae at per-container rates comparable to baseline, with barrels sustaining higher productivity than zeers.

The decrease in vector density is a combined effect of the control interventions and the wet to dry seasonal transition. Combining Stegomyia indices with per-container productivity identifies and quantifies residual containers sustaining the vector population. Sustained post-outbreak surveillance is needed, as these residual containers may contribute to vector population resurgence during subsequent transmission seasons.