Entomological surveys and insecticide susceptibility profile of Aedes aegypti during the dengue outbreak in Sao Tome and Principe in 2022

BackgroundThe first dengue outbreak was reported in Sao Tome and Principe in 2022. This study was undertaken aiming to establish the typology of Aedes larval habitats, the distribution of Ae. aegypti and Ae. albopictus, the related entomological risk and the susceptibility profile of Ae. aegypti to insecticides for a better evidence-informed response. Methodology/Principal FindingsEntomological surveys were performed in all the seven health districts of Sao tome and Principe during the dry and rainy seasons in 2022. WHO tube and synergist assays using piperonyl butoxide (PBO) and diethyl maleate (DEM) were carried out and the genotyping of F1534C/V1016I/V410L mutations in Ae. aegypti. Aedes aegypti and Ae. albopictus were found in all seven health districts of the country with high prevalence of Ae. aegypti in the most urbanised district, Agua Grande. Both Aedes species bred mainly in used tyres, discarded tanks and water storage containers. In both survey periods, the Breteau (BI > 50), house (HI > 35%) and container (CI > 20%) indices were higher than threshold established by WHO to indicate high potential risk of dengue transmission. Aedes aegypti sample was susceptible to all insecticides tested except dichlorodiphenyltrichloroethane (DDT) (9.2% mortality), bendiocarb (61.4% mortality) and alpha-cypermethrin (97% mortality). A full recovery was reported in Ae. aegypti resistant to bendiocarb after pre-exposure to synergist PBO. Only one Ae. aegypti specimen was found carrying F1534C mutation. Conclusions/SignificanceThese findings revealed at high potential risk for dengue transmission throughout the year, with the bulk of larval breeding occurring in used tyres, water storage and discarded containers. Most of the insecticides tested remain effective to control Aedes vectors in Sao Tome except DDT and bendiocarb. These data underline the importance to raise community awareness and to implement routine dengue vector control strategies to prevent further outbreaks in Sao Tome and Principe, and elsewhere in the subregion. Author SummaryDuring the first dengue outbreak reported in Sao Tome and Principe in 2022, entomological investigations were undertaken aiming to establish the typology of Aedes larval habitats, the distribution of Ae. aegypti and Ae. albopictus, the related entomological risk and the susceptibility profile of Ae. aegypti to insecticides for a better evidence-informed response. The results revealed the presence of Ae. aegypti and Ae. albopictus in all seven health districts of the country with high prevalence of Ae. aegypti in the most urbanised district, Agua Grande. Both Aedes species bred mainly in used tyres, discarded tanks and water storage containers suggesting a good waste management and improving water supply system could help to reduce Aedes densities and the risk of dengue transmission. Analyses also revealed that most of the insecticides tested remain effective to control Aedes vectors in Sao Tome except dichlorodiphenyltrichloroethane and bendiocarb. These findings revealed at high potential risk for dengue transmission throughout the year and underline the importance to raise community awareness and to implement routine dengue vector control strategies to prevent further outbreaks in Sao Tome and Principe, and elsewhere in the subregion.