Insecticide resistance in dengue vectors from hotspots in Selangor, Malaysia

Background In Malaysia, dengue remains a top priority disease and usage of insecticides is the main method for dengue vector control. Limited baseline insecticide resistance data in dengue hotspots has prompted us to conduct this study. The present study reports the use of a map on the insecticide susceptibility status of Aedes aegypti and Aedes albopictus to provide a quick visualization and overview of the distribution of insecticide resistance. Method and results The insecticide resistance status of Aedes populations collected from 24 dengue hotspot areas from the period of December 2018 until June 2019 was proactively monitored using the World Health Organization standard protocol for adult and larval susceptibility testing was conducted, together with elucidation of the mechanisms involved in observed resistance. For resistance monitoring, susceptibility to three adulticides (permethrin, deltamethrin, and malathion) was tested, as well as susceptibility to the larvicide, temephos. Data showed significant resistance to both deltamethrin and permethrin (pyrethroid insecticides), and to malathion (organophosphate insecticide) in all sampled Aedes aegypti populations, while variable resistance patterns were found in the sampled Aedes albopictus populations. Temephos resistance was observed when larvae were tested using the diagnostic dosage of 0.012mg/L but not at the operational dosage of 1mg/L for both species. Conclusion The present study highlights evidence of a potential threat to the effectiveness of insecticides currently used in dengue vector control, and the urgent requirement for insecticide resistance management to be integrated into the National Dengue Control Program.
Author summary Insecticide resistance may threaten the efficacy of insecticides currently used in the dengue vector control program. These current findings reveal widespread insecticide resistance in Aedes aegypti and Aedes albopictus sampled from dengue hotspots. This screening provides comprehensive data on insecticide resistance to insecticides commonly used in dengue vector control programs. The mapping approach utilized in this present study facilitates easy visualization of the resistance distribution in dengue vectors across many dengue hotspots. Therefore, it could hence be beneficial to the Ministry of Health in managing the threat of resistance before it compromises current dengue vector control strategies.