Abstract
BackgroundSichuan province is located in the southwest of China, and was previously a malaria-endemic region. Although no indigenous malaria case has been reported since 2011, the number of imported cases is on the rise. Insecticide-based vector control has played a central role in the prevention of malaria epidemics. However, the efficacy of this strategy is gravely challenged by the development of insecticide resistance. Regular monitoring of insecticide resistance is essential to inform evidence-based vector control. Unfortunately, almost no information is currently available on the status of insecticide resistance and associated mechanisms in Anopheles sinensis, the dominant malaria vector in Sichuan. In this study, efforts were invested in detecting the presence and frequency of insecticide resistance-associated mutations in three genes that encode target proteins of several classes of commonly used insecticides.MethodsA total of 446 adults of An. sinensis, collected from 12 locations across Sichuan province of China, were inspected for resistance-conferring mutations in three genes that respectively encode acetylcholinesterase (AChE), voltage-gated sodium channel (VGSC), and GABA receptor (RDL) by DNA Sanger sequencing.ResultsThe G119S mutation in AChE was detected at high frequencies (0.40–0.73). The predominant ace-1 genotype was GGC/AGC (119GS) heterozygotes. Diverse variations at codon 1014 were found in VGSC, leading to three different amino acid substitutions (L1014F/C/S). The 1014F was the predominant resistance allele and was distributed in all 12 populations at varying frequencies from 0.03 to 0.86. The A296S mutation in RDL was frequently present in Sichuan, with 296SS accounting for more than 80% of individuals in six of the 12 populations. Notably, in samples collected from Chengdu (DJY) and Deyang (DYMZ), almost 30% of individuals were found to be resistant homozygotes for all three targets.ConclusionsResistance-related mutations in three target proteins of the four main classes of insecticides were prevalent in most populations. This survey reveals a worrisome situation of multiple resistance genotypes in Sichuan malaria vector. The data strengthen the need for regular monitoring of insecticide resistance and establishing a region-customized vector intervention strategy.Graphical abstract
Highlights
Sichuan province is located in the southwest of China, and was previously a malaria-endemic region
Vector control has played an essential role in the prevention of epidemics caused by indigenous cases and secondary infections induced by imported cases [3]
Anopheles sinensis adults used in the study were caught around pigsties or cowsheds by light traps between August and September 2018 from 12 locations across Sichuan province of China
Summary
Sichuan province is located in the southwest of China, and was previously a malaria-endemic region. Insecticide-based vector control has played a central role in the prevention of malaria epidemics. Regular monitoring of insecticide resistance is essential to inform evidence-based vector control. Vector control has played an essential role in the prevention of epidemics caused by indigenous cases and secondary infections induced by imported cases [3]. The control of malaria vectors has relied primarily on the use of various classes of insecticides via either indoor residual spraying (IRS) or treatment of bed nets. Organochlorines, organophosphates, carbamates, and pyrethroids are four groups of insecticides recommended by WHO for indoor residual spraying [4]. These insecticides have been heavily used in agriculture. The intensive use of these insecticides in mosquito-targeted control and in agriculture has led to widespread insecticide resistance in malaria vector species [5]
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