Entomological surveys and insecticide susceptibility profile ofAedes aegyptiduring the dengue outbreak in Sao Tome and Principe in 2022
Authors: Kamgang Basile , Acântara João , Tedjou Armel , Keumeni Christophe , Yougang Aurelie , Ancia Anne , Bigirimana Françoise , Clarke Sian , Gil Vilfrido Santana , Wondji Charles 
Published: January 2024

Background

The first dengue outbreak was reported in Sao Tome and Principe in 2022. This study was undertaken aiming to establish the typology ofAedeslarval habitats, the distribution ofAe. aegyptiandAe. albopictus,the related entomological risk and the susceptibility profile ofAe. aegyptito insecticides for a better evidence-informed response.

Methodology/Principal Findings

Entomological 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 inAe. aegypti.Aedes aegyptiandAe. albopictuswere found in all seven health districts of the country with high prevalence ofAe. aegyptiin the most urbanised district, Agua Grande. BothAedesspecies 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 aegyptisample 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 inAe. aegyptiresistant to bendiocarb after pre-exposure to synergist PBO. Only oneAe. aegyptispecimen was found carrying F1534C mutation.

Conclusions/Significance

These 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 controlAedesvectors 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 Summary

During the first dengue outbreak reported in Sao Tome and Principe in 2022, entomological investigations were undertaken aiming to establish the typology ofAedeslarval habitats, the distribution ofAe. aegyptiandAe. albopictus,the related entomological risk and the susceptibility profile ofAe. aegyptito insecticides for a better evidence-informed response. The results revealed the presence ofAe. aegyptiandAe. albopictusin all seven health districts of the country with high prevalence ofAe. aegyptiin the most urbanised district, Agua Grande. BothAedesspecies bred mainly in used tyres, discarded tanks and water storage containers suggesting a good waste management and improving water supply system could help to reduceAedesdensities and the risk of dengue transmission. Analyses also revealed that most of the insecticides tested remain effective to controlAedesvectors 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.