Insecticide resistance in dengue vectors

Background Most national dengue control programmes rely extensively on insecticides to control the mosquito vectors of this disease. Objectives The objective of this review is to describe current knowledge of the extent of insecticide resistance in dengue vectors and the potential impact of this resistance on control activities. Methods We searched Web of Science and PubMed for studies that included data on resistance to the four major classes of insecticides: organochlorines, carbamates, organophosphates and pyrethroids, in the dengue vectors Aedes aegypti and Aedes albopictus. Insecticide bioassay data were extracted from the published literature and the methods used to obtain, analyse and interpret this data were critically evaluated. Emphasis was placed on the two insecticide classes most widely used in dengue control, organophosphates and pyrethroids. The use of biochemical and molecular tools for resistance monitoring was also reviewed. Results 103 studies met our inclusion criteria, of which 65 contained bioassay data which we uploaded on to a public database (IRBase). There is a strong geographical bias in published studies with nearly half originating from three countries (Thailand, India and Brazil). Bioassay data demonstrate that resistance to the organophosphate temephos and to pyrethroids is widespread in Ae. aegypti and resistance has also been reported in Ae. albopictus. Assessing the impact of insecticide resistance on vector control is complicated by variations in the methodology used to measure and report resistance, and by the lack of studies into the epidemiological consequences of insecticide resistance. Conclusions The lack of publicly accessible standardized data sets documenting levels of insecticide resistance in many dengue endemic countries, and the absence of studies on the operational impact of resistance, precludes a comprehensive analysis of the current global threat that insecticide resistance poses to dengue control. However, several countries with active resistance monitoring programmes have shown that insecticide resistance is reducing our ability to control dengue vectors. This situation is likely to worsen unless effective strategies are rapidly implemented to mitigate these effects.