Voltage-sensitive sodium channel (Vssc) mutations associated with pyrethroid insecticide resistance in Aedes aegypti (L.) from two districts of Jeddah, Kingdom of Saudi Arabia: baseline information for a Wolbachia release program

Abstract

Background Dengue suppression often relies on control of the mosquito vector, Aedes aegypti, through applications of insecticides of which the pyrethroid group has played a dominant role. Insecticide resistance is prevalent in Ae. aegypti around the world, and the resulting reduction of insecticide efficacy is likely to exacerbate the impact of dengue. Dengue has been a public health problem in Saudi Arabia, particularly in Jeddah, since its discovery there in the 1990s, and insecticide use for vector control is widespread throughout the city. An alternative approach to insecticide use, based on blocking dengue transmission in mosquitoes by the endosymbiont Wolbachia, is being trialed in Jeddah following the success of this approach in Australia and Malaysia. Knowledge of insecticide resistance status of mosquito populations in Jeddah is a prerequisite for establishing a Wolbachia-based dengue control program as releases of Wolbachia mosquitoes succeed when resistance status of the release population is similar to that of the wild population. Methods WHO resistance bioassays of mosquitoes with deltamethrin, permethrin and DDT were used in conjunction with TaqMan® SNP Genotyping Assays to characterize mutation profiles of Ae. aegypti. Results Screening of the voltage-sensitive sodium channel (Vssc), the pyrethroid target site, revealed mutations at codons 989, 1016 and 1534 in Ae. aegypti from two districts of Jeddah. The triple mutant homozygote (1016G/1534C/989P) was confirmed from Al Safa and Al Rawabi. Bioassays with pyrethroids (Type I and II) and DDT showed that mosquitoes were resistant to each of these compounds based on WHO definitions. An association between Vssc mutations and resistance was established for the Type II pyrethroid, deltamethrin, with one genotype (989P/1016G/1534F) conferring a survival advantage over two others (989S/1016V/1534C and the triple heterozygote). An indication of synergism of Type I pyrethroid activity with piperonyl butoxide suggests that detoxification by cytochrome P450s accounts for some of the pyrethroid resistance response in Ae. aegypti populations from Jeddah. Conclusions The results provide a baseline for monitoring and management of resistance as well as knowledge of Vssc genotype frequencies required in Wolbachia release populations to ensure homogeneity with the target field population. Vssc mutation haplotypes observed show some similarity with those from Ae. aegypti in southeast Asia and the Indo-Pacific, but the presence of the triple mutant haplotype in three genotypes indicates that the species in this region may have a unique population history. Graphical Abstract

Molecular analysis of knockdown resistance (kdr) mutations in the voltage-gated sodium channel gene of Aedes aegypti populations from Saudi Arabia

“…This study concurrently characterised kdr mutations in these dengue-endemic regions of Saudi Arabia by sequencing domains IIS6 and IIIS6 of vgsc and comparing them with the variation found in samples from Thailand, Myanmar and Uganda. The kdr mutations S989P, V1016G and F1534C have previously been reported from Makkah and Jeddah [ 18 , 35 , 56 ] and from a laboratory strain of Ae. aegypti from Jazan [ 57 ].…”

“…Frequencies of vgsc genotypes involving the three kdr mutations (S989P, V1016G and F1534C) vary among locations. To date, eight and 12 genotypes have been reported from Saudi Arabia and Myanmar, respectively, while Thailand has reported only three [ 30 , 35 , 38 ]. The genotype that is homozygous for mutations S989P and V1016G but is wild type at F1534C has a high resistance level to both type I (i.e.…”

“…permethrin) and type II (i.e. deltamethrin) pyrethroids [ 35 ]. In contrast, the genotype (S989P, V1016G wild type with F1534C homozygous mutant, i.e.…”

DevelopingWolbachia-based disease interventions for an extreme environment

“…The strong blockage of dengue virus (DENV2) by Wolbachia and particularly w MelM in the Jeddah genetic background provides confidence for mosquito releases aimed at population replacement to proceed in the Jeddah area. At present, dengue suppression in Jeddah is reliant on regular and widespread applications of pesticides, which is not sustainable in the long run due to both environmental costs and the evolution of resistance 57, 62 . It is still unclear how easily Wolbachia invasion will proceed within the Jeddah environment, and whether the replacement process can be facilitated through the selection of a particular Wolbachia strain and releases targeting a particular time of the year.…”

“…Releases of Ae. aegypti with Wolbachia strains are underway in Jeddah, Saudi Arabia for dengue control and preparatory work has been initiated to characterize the local mosquito population 57, 58 . The city of Jeddah has a climate with low rainfall (BWh; Hot Desert Climate) under the Koppen’s classification.…”