Frequency of kdr mutations in the voltage-sensitive sodium channel (VSSC) gene in Aedes aegypti from Yogyakarta and implications for Wolbachia-infected mosquito trials

Fine-scale monitoring of insecticide resistance in Aedes aegypti (Diptera: Culicidae) from Sri Lanka and modeling the phenotypic resistance using rational approximation

BACKGROUND

The unplanned and intensified use of insecticides to control mosquito-borne diseases has led to an upsurge of resistance to commonly used insecticides. Aedes aegypti, the main vector of dengue, chikungunya, and Zika virus, is primarily controlled through the application of adulticides (pyrethroid insecticides) and larvicides (temephos). Fine spatial-scale analysis of resistance may reveal important resistance-related patterns, and the application of mathematical models to determine the phenotypic resistance status lessens the cost and usage of resources, thus resulting in an enhanced and successful control program.

METHODS

The phenotypic resistance for permethrin, deltamethrin, and malathion was monitored in the Ae. aegypti populations using the World Health Organization (WHO) adult bioassay method. Mosquitoes' resistance to permethrin and deltamethrin was evaluated for the commonly occurring base substitutions in the voltage-gated sodium channel (vgsc) gene. Rational functions were used to determine the relationship between the kdr alleles and the phenotypic resistant percentage of Ae. aegypti in Sri Lanka.

RESULTS

The results of the bioassays revealed highly resistant Ae. aegypti populations for the two pyrethroid insecticides (permethrin and deltamethrin) tested. All populations were susceptible to 5% malathion insecticide. The study also revealed high frequencies of C1534 and G1016 in all the populations studied. The highest haplotype frequency was detected for the haplotype CC/VV, followed by FC/VV and CC/VG. Of the seven models obtained, this study suggests the prediction models using rational approximation considering the C allele frequencies and the total of C, G, and P allele frequencies and phenotypic resistance as the best fits for the area concerned.

CONCLUSIONS

This is the first study to our knowledge to provide a model to predict phenotypic resistance using rational functions considering kdr alleles. The flexible nature of the rational functions has revealed the most suitable association among them. Thus, a general evaluation of kdr alleles prior to insecticide applications would unveil the phenotypic resistance percentage of the wild mosquito population. A site-specific strategy is recommended for monitoring resistance with a mathematical approach and management of insecticide applications for the vector population.

INSECTICIDE SUSCEPTIBILITY AND DETECTION OF kdr-GENE MUTATIONS IN AEDES AEGYPTI OF PESHAWAR, PAKISTAN

Dengue is a common disease in Peshawar, Pakistan whose primary vector is Aedes aegypti mosquito. Due to absence of vaccines and proper drugs for dengue, vector control is a necessary tool. Insecticide resistance in vectors is a threat to the control of dengue vector. This study presents the susceptibility status of Ae. aegypti to eight insecticides in district Peshawar and screen the mutations in knock down resistant gene (kdr). Ae. aegypti were found highly resistant to DDT and Deltamethrin while highly susceptible to Cyfluthrin and Bendiocarb. DNA sequencing of two domains (II and III) of kdr-gene have detected four SNPs in domain IIS6 at positions S989P and V1016G and two mutations at position T1520I and F1534C in domain IIIS6. Results showed a low frequency i.e. 0.19 and 0.12 for S989P and V1016G, moderate for T1520I (0.42) and high frequency for F1534C (0.86). Mutational combinations showed that the predominant combination was SSVVTICC (43%) in which T1520I was heterozygous and F1534C was homozygous mutant. This study will be helpful in designing vector control strategies for the control of dengue in the studied area and will provide first knowledge about Kdr gene mutations that confer resistance in this species.

Updating the Insecticide Resistance Status of Aedes aegypti and Aedes albopictus in Asia: A Systematic Review and Meta-Analysis

Background: Aedes aegypti and Aedes albopictus are two important vectors of several important arboviruses, including the dengue, chikungunya, and Zika viruses. Insecticide application is an important approach to reduce vector abundance during Aedes spp.-borne outbreaks in the absence of effective vaccines and treatments. However, insecticide overuse can result in the development of resistance, and careful monitoring of resistance markers is required. Methods: This meta-analysis and systematic review explored the spatial and temporal patterns of insecticide resistance in Asia from 2000 to 2021. PubMed, Scopus, EbscoHost, and Embase were used to enhance the search capability. The random-effects model was applied for the 94 studies that met our inclusion criteria for qualitative synthesis and meta-analysis. Results: Four major insecticides were studied (malathion, dichlorodiphenyltrichloroethane, permethrin, and deltamethrin). Dichlorodiphenyltrichloroethane resistance rates were high in both Ae. aegypti and Ae. albopictus (68% and 64%, respectively). Conversely, malathion resistance was less prevalent in Ae. aegypti (3%), and deltamethrin resistance was less common in Ae. albopictus (2%). Ae. aegypti displayed consistently high resistance rates (35%) throughout the study period, whereas the rate of insecticide resistance in Ae. albopictus increased from 5% to 12%. The rates of the major kdr mutations F1534C, V1016G, and S989P were 29%, 26%, and 22%, respectively. Conclusions: Insecticide resistance in both Ae. aegypti and Ae. albopictus is widespread in Asia, although the rates vary by country. Continuous monitoring of the resistance markers and modification of the control strategies will be important for preventing unexpected outbreaks. This systematic review and meta-analysis provided up-to-date information on insecticide resistance in dengue-endemic countries in Asia.

Rapid detection of kdr mutation F1534C in Aedes aegypti using recombinase polymerase amplification and lateral flow dipsticks

Insecticide resistance monitoring is essential in assessing the efficacy of vector control measures. However, gold standard PCR-based molecular analyses for insecticide resistance detection are often hindered by time-consuming sample processing, as well as considerable infrastructure and resourcing requirements. In this study, we combined a novel one-step sample preparation reagent with a rapid isothermal molecular test that detects a knock down resistance (kdr) mutation (F1534C) that enables pyrethroid resistance in Aedes aegypti mosquitoes. We trialled the rapid F1534C pyrethroid resistance test using insecticide resistant Ae. aegypti mosquito bodies and compared results to a conventional, allele-specific quantitative PCR (AS-qPCR) coupled with melt curve genotyping in corresponding mosquito heads. From a strain of Ae. aegypti established from an insecticide resistant population in Merida, Mexico (n = 27), all the mosquito bodies (n = 27) tested positive with the rapid F1534C test regardless of whether they were homozygous or heterozygous. To assess diagnostic test specificity, we confirmed that F1534 was not detected in laboratory-reared, fully susceptible Ae. aegypti mosquito bodies (n = 28) using the rapid F1534C test or the conventional AS-qPCR melt curve analysis. All corresponding mosquito heads (n = 28) were homozygous wild-type FF1534. The rapid F1534C test thus demonstrated 100% diagnostic sensitivity (95% CI: 87.23% to 100%) and 100% diagnostic specificity (95% CI: 87.66% to 100.00%) for detection of the F1534C pyrethroid resistant single nucleotide polymorphism (SNP) in both heterozygous and homozygous Ae. aegypti. In the collection of mutant mosquitoes from Mexico, CC1534 homozygous mutants occurred at a frequency of 74.1% (n = 20) and FC heterozygous mutants at a frequency of 25.9% (n = 7). The rapid F1534C test significantly reduced the sample processing and testing time from approximately 6 h for the AS-qPCR melt curve analysis to only 25 min. These results demonstrate significant potential for our approach to resistance testing as a field-based, low-resource, rapid alternative to time-consuming and expensive laboratory-based detection.

Detection and Co-occurrence of kdr (F1534C and S989P) Mutations in Multiple Insecticides Resistant Aedes aegypti (Diptera: Culicidae) in Nigeria

The outbreak of yellow fever virus transmitted by Aedes aegypti has been of major concern in Nigeria, this mosquito also transmits several other arboviruses globally. The control of many vectors of mosquito-borne diseases relies heavily on the use of insecticides. Therefore, constant monitoring of insecticide resistance status and associated mechanisms is crucial within the local mosquito population. Here, we determined the resistance profile of adult Ae. aegypti from Majidun and Oke Ota communities, Ikorodu Local Government Area of Lagos State, Nigeria to different classes of insecticides using WHO procedures. The resistant phenotypes of Ae. aegypti were screened for the presence of kdr mutations F1534C, S989P, and V1016G, which have been implicated in insecticide resistance in yellow fever vectors. A high level of resistance to DDT and pyrethroids was recorded in Ae. aegypti in this study, although possible resistance to deltamethrin, one of the pyrethroids was reported in one of the locations. Resistance to bendiocarb was recorded in the Majidun community while Ae. aegypti in both locations were susceptible to malathion. The presence of F1534C mutation associated with DDT and deltamethrin resistance in Ae. aegypti population, and the presence of S989P mutation were detected singly and in co-occurrence with F1534C for the first time in Africa, while V1016G mutation was not detected in this study. The role of these mutations in resistance phenotype expressed in Ae. aegypti in larger populations needs to be established.

Insecticide Resistance Profiles and Synergism of Field Aedes aegypti from Indonesia

Information on the insecticide resistance profiles of Aedes aegypti in Indonesia is fragmentary because of the lack of wide-area insecticide resistance surveillance. We collected Ae. aegypti from 32 districts and regencies in 27 Indonesian provinces and used WHO bioassays to evaluate their resistance to deltamethrin, permethrin, bendiocarb, and pirimiphos-methyl. To determine the possible resistance mechanisms of Ae. aegypti, synergism tests were conducted using piperonyl butoxide (PBO) and S,S,S-tributylphosphorotrithioates (DEF). The Ae. aegypti from all locations exhibited various levels of resistance to pyrethroids. Their resistance ratio (RR₅₀) to permethrin and deltamethrin ranged from 4.08× to 127× and from 4.37× to 72.20×, respectively. In contrast with the findings of other studies, most strains from the highly urbanized cities on the island of Java (i.e., Banten, Jakarta, Bandung, Semarang, Yogyakarta, and Surabaya) exhibited low to moderate resistance to pyrethroids. By contrast, the strains collected from the less populated Kalimantan region exhibited very high resistance to pyrethroids. The possible reasons are discussed herein. Low levels of resistance to bendiocarb (RR₅₀, 1.24–6.46×) and pirimiphos-methyl (RR₅₀, 1.01–2.70×) were observed in all tested strains, regardless of locality. PBO and DEF synergists significantly increased the susceptibility of Ae. aegypti to permethrin and deltamethrin and reduced their resistance ratio to less than 16×. The synergism tests suggested the major involvement of cytochrome P450 monooxygenases and esterases in conferring pyrethroid resistance. On the basis of our results, we proposed a 6-month rotation of insecticides (deltamethrin + synergists ➝ bendiocarb ➝ permethrin + synergists ➝ pirimiphos-methyl) and the use of an insecticide mixture containing pyrethroid and pyrimiphos-methyl to control Ae. aegypti populations and overcome the challenge of widespread Ae. aegypti resistance to pyrethroid in Indonesia.

Insecticide resistance is a major impediment to the successful management of vector-transmitted diseases because it increases the vector’s chances of surviving under insecticide treatment. In Indonesia, the implementation of insecticide resistance management at the national level is particularly challenging due to the vast area and regional disparities in terms of population, health, and socioeconomic status. Previous studies on determining insecticide resistance of Aedes mosquito only focused on several cities in some provinces of Indonesia, making resistance monitoring results difficult to interpret and arguably reflect the generality in Indonesia. To complicate the matter, data released by the Ministry of Agriculture of Indonesia in 2022 showed that approximately 82% of insecticides registered to control Ae. aegypti in Indonesia are pyrethroid-based products. Principally, we found that the synergists PBO and DEF significantly reduce the resistance of field Ae. aegypti from Indonesia toward permethrin and deltamethrin. Bendiocarb and pirimiphos-methyl remain highly toxic to the field strains of Ae. aegypti. We suggest the feasible choice of insecticide group for Ae. aegypti vector management based on the currently registered insecticide inventory. The finding also underscores the urgent need to approve other non-pyrethroid-based insecticides as alternative tools for reducing the risk of resistance development during an outbreak.

Aedes aegypti abundance and insecticide resistance profiles in the Applying Wolbachia to Eliminate Dengue trial

The Applying Wolbachia to Eliminate Dengue (AWED) trial was a parallel cluster randomised trial that demonstrated Wolbachia (wMel) introgression into Ae. aegypti populations reduced dengue incidence. In this predefined substudy, we compared between treatment arms, the relative abundance of Ae. aegypti and Ae. albopictus before, during and after wMel-introgression. Between March 2015 and March 2020, 60,084 BG trap collections yielded 478,254 Ae. aegypti and 17,623 Ae. albopictus. Between treatment arms there was no measurable difference in Ae. aegypti relative abundance before or after wMel-deployments, with a count ratio of 0.96 (95% CI 0.76, 1.21) and 1.00 (95% CI 0.85, 1.17) respectively. More Ae. aegypti were caught per trap per week in the wMel-intervention arm compared to the control arm during wMel deployments (count ratio 1.23 (95% CI 1.03, 1.46)). Between treatment arms there was no measurable difference in the Ae. albopictus population size before, during or after wMel-deployment (overall count ratio 1.10 (95% CI 0.89, 1.35)). We also compared insecticide resistance phenotypes of Ae. aegypti in the first and second years after wMel-deployments. Ae. aegypti field populations from wMel-treated and untreated arms were similarly resistant to malathion (0.8%), permethrin (1.25%) and cyfluthrin (0.15%) in year 1 and year 2 of the trial. In summary, we found no between-arm differences in the relative abundance of Ae. aegypti or Ae. albopictus prior to or after wMel introgression, and no between-arm difference in Ae. aegypti insecticide resistance phenotypes. These data suggest neither Aedes abundance, nor insecticide resistance, confounded the epidemiological outcomes of the AWED trial.

Dengue is a mosquito-borne viral disease and a major public health problem in the tropical and subtropical world. It is caused by any of the four dengue virus serotypes. In a previously published randomised clinical trial, called the AWED trial, we demonstrated that releases of Aedes aegypti mosquitoes infected with the insect bacterium Wolbachia can reduce the case incidence of dengue by 77%. In this current study, we compared the abundance of Ae. aegypti mosquitoes in the neighbourhoods where Wolbachia-infected mosquitoes were released versus the untreated neighbourhoods. This was important to do so that scientists could understand the mechanism for how Wolbachia releases reduced dengue incidence. Between March 2015 and March 2020, we did not observe any differences in Ae. aegypti abundance before or after Wolbachia-deployments in the AWED trial area. There was also no difference in the abundance of the related mosquito, Ae. albopictus, before, during or after wMel-deployment. We also compared insecticide resistance characteristics amongst Ae. aegypti in the first and second years after Wolbachia -deployments and found no difference between mosquitoes from Wolbachia-treated and untreated neighbourhoods. These data suggest neither Aedes abundance, nor insecticide resistance, were confounding sources to the epidemiological outcomes of the AWED trial.