Tracing temporal and geographic distribution of resistance to pyrethroids in the arboviral vector Aedes albopictus.

Author summary Aedes albopictusis a highly invasive mosquito and a vector for a number of arboviruses. The arrival and establishment ofAe.albopictusin temperature regions of the world, such as Europe, has been accompanied by re-emergence of arboviral diseases. There are no effective therapeutic treatments for arboviruses meaning control of vector populations is the primary strategy to prevent arboviral disease transmission. Pyrethroids are frequently used for control of vectors based on their low mammalian toxicity and rapid knockdown effect on mosquitoes. The identification of mutations predictive of resistance phenotype in theparasodium channel gene, the target site of pyrethroids, has provided for molecular markers to test for resistance by genotyping wild-collected mosquitoes. Here we analysed all currently known predictive mutations for pyrethroid resistance in 512 geographic mosquitoes sampled in a span of seven years. Thus, we are able to add a temporal dimension to the analysis of geographic distribution of resistance alleles. Overall our data confirm a patchy distribution of mutations predictive of the resistance phenotype, but also reveal an alarming increase of resistance mutations in China, Greece and Italy. Resistance mutations appear to have arisen locally more than being spread through mosquito migration/invasions. Background The arboviral vectorAedes albopictusbecame established on all continents except Antarctica in the past 50 years. A consequence of its rapid global invasion is the transmission of diseases previously confined to the tropics and subtropics occurring in temperate regions of the world, including the re-emergence of chikungunya and dengue in Europe. Application of pyrethroids is among the most widely-used interventions for vector control, especially in the presence of an arboviral outbreak. Studies are emerging that reveal phenotypic resistance and monitor mutations at the target site, theparasodium channel gene, primarily on a local scale. Methods A total of 512Ae.albopictusmosquitoes from twelve geographic sites, including those from the native home range and invaded areas, were sampled between 2011 and 2018, and were analyzed at five codons of theparasodium channel gene with mutations predictive of resistance phenotype. Additionally, to test for the origin of uniquekdrmutations in Mexico, we analyzed the genetic connectivity of southern Mexico mosquitoes with mosquitoes from home range, the Reunion Island, America and Europe. Results We detected mutations at all tested positions of theparasodium channel gene, with heterozygotes predominating and rare instance of double mutants. We observed an increase in the distribution and frequency of F1534C/L/S mutations in the ancestral China population and populations in the Mediterranean Greece, the appearance of the V1016G/I mutations as early as 2011 in Italy and mutations at position 410 and 989 in Mexico. The analyses of the distribution pattern ofkdralleles and haplotype network analyses showed evidence for multiple origins of allkdrmutations. Conclusions Here we provide the most-up-to-date survey on the geographic and temporal distribution of pyrethroid-predictive mutations inAe.albopictusby combiningkdrgenotyping on current and historical samples with published data. While we confirm low levels of pyrethroid resistance in most analyzed samples, we find increasing frequencies of F1534C/S and V1016G in China and Greece or Italy, respectively. The observed patterns ofkdrallele distribution support the hypothesis that on site emergence of resistance has contributed more than spread of resistance through mosquito migration/invasions to the current widespread ofkdralleles, emphasizing the importance of local surveillance programs and resistance management.