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 bioassy 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: 66 studies met our inclusion criteria and were uploaded on to a public databse (IRBase). There is a stong geographical bias in published studies with nearly half originating from three countries (Thailand, India and Brazil). Bioassay data demonstrates 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 insecticicde resistance. Conclusions: The lack of publicly accessible standardized data sets dcoumenting levels of insecticide resistance in many dengue endemic countries, and the absence of studies on the operational impact of resistance, preculdes 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

Population genomics reveals that an anthropophilic population of Aedes aegypti\textit{Aedes aegypti} mosquitoes in West Africa recently gave rise to American and Asian populations of this major disease vector

$\textbf{BACKGROUND}$: The mosquito $\textit{Aedes aegypti}$ is the main vector of dengue, Zika, chikungunya and yellow fever viruses. This major disease vector is thought to have arisen when the African subspecies $\textit{Ae. aegypti}$ formosus evolved from being zoophilic and living in forest habitats into a form that specialises on humans and resides near human population centres. The resulting domestic subspecies, $\textit{Ae. aegypti aegypti}$, is found throughout the tropics and largely blood-feeds on humans. $\textbf{RESULTS}$: To understand this transition, we have sequenced the exomes of mosquitoes collected from five populations from around the world. We found that $\textit{Ae. aegypti}$ specimens from an urban population in Senegal in West Africa were more closely related to populations in Mexico and Sri Lanka than they were to a nearby forest population. We estimate that the populations in Senegal and Mexico split just a few hundred years ago, and we found no evidence of $\textit{Ae. aegypti aegypti}$ mosquitoes migrating back to Africa from elsewhere in the tropics. The out-of-Africa migration was accompanied by a dramatic reduction in effective population size, resulting in a loss of genetic diversity and rare genetic variants. $\textbf{CONCLUSIONS}$: We conclude that a domestic population of $\textit{Ae. aegypti}$ in Senegal and domestic populations on other continents are more closely related to each other than to other African populations. This suggests that an ancestral population of $\textit{Ae. aegypti }$evolved to become a human specialist in Africa, giving rise to the subspecies $\textit{Ae. aegypti aegypti}$. The descendants of this population are still found in West Africa today, and the rest of the world was colonised when mosquitoes from this population migrated out of Africa. This is the first report of an African population of Ae. aegypti aegypti mosquitoes that is closely related to Asian and American populations. As the two subspecies differ in their ability to vector disease, their existence side by side in West Africa may have important implications for disease transmission.This work was funded by European Research Council grant Drosophila Infection 281668 to FMJ, a KAUST AEA award to FMJ and AP, a Medical Research Council Centenary Award to WJP and a National Institutes of Health Ruth L. Kirschstein National Research Service Award to JC

Improved reference genome of Aedes aegypti informs arbovirus vector control

Female Aedes aegypti mosquitoes infect more than 400 million people each year with dangerous viral pathogens including dengue, yellow fever, Zika and chikungunya. Progress in understanding the biology of mosquitoes and developing the tools to fight them has been slowed by the lack of a high-quality genome assembly. Here we combine diverse technologies to produce the markedly improved, fully re-annotated AaegL5 genome assembly, and demonstrate how it accelerates mosquito science. We anchored physical and cytogenetic maps, doubled the number of known chemosensory ionotropic receptors that guide mosquitoes to human hosts and egg-laying sites, provided further insight into the size and composition of the sex-determining M locus, and revealed copy-number variation among glutathione S-transferase genes that are important for insecticide resistance. Using high-resolution quantitative trait locus and population genomic analyses, we mapped new candidates for dengue vector competence and insecticide resistance. AaegL5 will catalyse new biological insights and intervention strategies to fight this deadly disease vector