Biology subjects

Lynd, A.

Publications and source records attributed to Lynd, A..

5 recordsLinked to original sources

bioRxiv2022

The durability of long-lasting insecticidal nets treated with and without piperonyl butoxide (PBO) in Uganda.

Long Lasting Insecticidal Nets (LLINs) supplemented with the synergist piperonyl butoxide have been developed in response to growing pyrethroid resistance however their durability in the field remains poorly described. A pragmatic cluster-randomised trial was embedded into Ugandas 2017-2018 distribution to compare the durability of LLINs with and without PBO A total of 104 clusters were included with each receiving one of four LLIN products, two with pyrethroid+PBO (Olyset Plus and PermaNet 3.0) and two pyrethroid-only (Olyset Net and PermaNet 2.0). Nets were sampled at baseline, 12, and 25 months post-distribution to assess physical condition, chemical content, and bioefficacy. Physical condition was quantified using proportionate Hole Index and chemical content measured using high-performance liquid chromatography. Bioefficacy was assessed with three-minute WHO Cone and Wireball assays using pyrethroid-resistant An. gambiae, with 1hr knockdown and 24hr mortality recorded. There was no difference in physical durability between LLIN products assessed (p=0.644). The pyrethroid content of all products remained relatively stable across timepoints but PBO content declined by 55% (p<0.001) and 58% (p<0.001) for Olyset Plus and PermaNet 3.0 respectively. Both PBO LLINs were highly effective against pyrethroid-resistant mosquitoes when new, knocking down all mosquitoes. However, bioefficacy declined over time with Olyset Plus knocking down 45.72% (95% CI: 22.84-68.62, p=0.021) and Permanet 3.0 knocking down 78.57% (95% CI: 63.57-93.58, p<0.001) after 25 months. Here we demonstrate that both Olyset Plus and PermaNet 3.0 are as durable as their pyrethroid-only equivalents and had superior bioefficacy against pyrethroid-resistant An. gambiae. However, the superiority of PBO-LLINs decreased with operational use, correlating with a reduction in total PBO content. This decline in bioefficacy after just two years is concerning and there is an urgent need to assess the durability of PBO LLINs in other settings.

zoology↗

bioRxiv2021

Modelling spatiotemporal trends in the frequency of genetic mutations conferring insecticide target-site resistance in African malaria vector species

Resistance in malaria vectors to pyrethroids, the most widely used class of insecticides for malaria vector control, threatens the continued efficacy of vector control tools. Target-site resistance is an important genetic resistance mechanism caused by mutations in the voltage-gated sodium channel (Vgsc) gene that encodes the pyrethroid target-site. Understanding the geographic distribution of target-site resistance, and temporal trends across different vector species, can inform strategic deployment of vector control tools. Here we develop a Bayesian statistical spatiotemporal model to interpret species-specific trends in the frequency of the most common resistance mutations, Vgsc-995S and Vgsc-995F, in three major malaria vector species Anopheles gambiae, An. coluzzii, and An. arabiensis. For nine selected countries, we develop annual predictive maps which reveal geographically-structured patterns of spread of each mutation at regional and continental scales. The results show associations, as well as stark differences, in spread dynamics of the two mutations across the three vector species. The coverage of ITNs was an influential predictor of Vgsc allele frequencies in our models. Our mapped Vgsc allele frequencies are a significant partial predictor of phenotypic resistance to the pyrethroid deltamethrin in An. gambiae complex populations, highlighting the importance of molecular surveillance of resistance mechanisms.

genetics↗

bioRxiv2021

Identification of a rapidly-spreading triple mutant for high-level metabolic insecticide resistance in Anopheles gambiae provides a real-time molecular diagnostic for anti-malarial intervention deployment.

Insecticide resistance provides both an increasingly pressing threat to the control of vector-borne diseases and insights into the remarkable capacity of natural populations to show rapid evolutionary responses to contemporary selection. Malaria control remains heavily dependent on deployment of pyrethroid insecticides, primarily in long lasting insecticidal nets (LLINs), but resistance in the major malaria vectors has increased over the last 15 years in concert with dramatic expansion of LLIN distributions. Identifying genetic mechanisms underlying high-level resistance in mosquitoes, which may almost entirely overcome pyrethroid efficacy, is crucial for the development and deployment of potentially resistance-breaking tools. Using the Anopheles gambiae 1000 genomes (Ag1000g) data we identified a very recent selective sweep in mosquitoes from Uganda which localized to a cluster of cytochrome P450 genes, including some commonly implicated in resistance. Further interrogation revealed a haplotype involving a trio of mutations, a nonsynonymous point mutation in Cyp6p4 (I236M), an upstream insertion of a partial Zanzibar-like transposable element (TE) and a duplication of the Cyp6aa1 gene. The mutations appear to have originated recently in An. gambiae from the Kenya-Uganda border region around Lake Victoria, with stepwise replacement of the double-mutant (Zanzibar-like TE and Cyp6p4-236M) with the triple-mutant haplotype (including Cyp6aa1 duplication), which has spread into the Democratic Republic of Congo and Tanzania. The triple-mutant haplotype is strongly associated with increased expression of genes able to metabolise pyrethroids and is strongly predictive of resistance to pyrethroids most notably deltamethrin, a commonly-used LLIN insecticide. Importantly, there was increased mortality in mosquitoes carrying the triple-mutation when exposed to nets co-treated with the synergist piperonyl butoxide (PBO). Frequencies of the triple-mutant haplotype remain spatially variable within countries, suggesting an effective marker system to guide deployment decisions for limited supplies of PBO-pyrethroid co-treated LLINs across African countries. Duplications of the Cyp6aa1 gene are common in An. gambiae across Africa and, given the enzymes metabolic activity, are likely to be a useful diagnostic for high levels of pyrethroid resistance.

evolutionary biology↗

bioRxiv2019

Development of a functional genetic tool for Anopheles gambiae oenocyte characterisation: application to cuticular hydrocarbon synthesis

Oenocytes are an insect cell type having diverse physiological functions ranging from cuticular hydrocarbon (CHC) production to insecticide detoxification that may impact their capacity to transmit pathogens. To develop functional genetic tools to study Anopheles gambiae oenocytes, we have trapped an oenocyte enhancer to create a transgenic mosquito Gal4 driver line that mediates tissue-specific expression. After crossing with UAS-reporter lines, An. gambiae oenocytes are fluorescently tagged through all life stages and demonstrate clearly the two characteristic oenocyte cell-types arising during development. The driver was then used to characterise the function of two oenocyte expressed An. gambiae cyp4g genes through tissue-specific expression of UAS-RNAi constructs. Silencing of cyp4g16 or cyp4g17 caused lethality in pupae of differing timing and penetrance. Surviving cyp4g16 knockdown adults showed increased sensitivity to desiccation. Total cuticular hydrocarbon levels were reduced by approximately 80% or 50% in both single gene knockdowns when assayed in young pupa or surviving adults respectively, indicating both genes are required for complete CHC production in An. gambiae and demonstrate synergistic activity in young pupae. Comparative CHC profiles were very similar for the two knockdowns, indicating overlapping substrate specificities of the two enzymes. Differences were observed for example with reduced abundance of shorter chain CHCs in CYP4G16 knockdowns, and reduction in longer, branched chained CHCs in CYP4G17 knockdown adults. This is the first time that two cyp4gs have both been shown to be required for complete CHC production in an insect. Moreover, the generation of tagged cells and identification of an enhancer region can expediate oenocyte specific transcriptomics. The novel driver line can also be used to explore oenocyte roles in pheromone production, mating behaviour and longevity in the malaria mosquito.

molecular biology↗

bioRxiv2019

A high throughput multi-locus insecticide resistance marker panel for tracking resistance emergence and spread in Anopheles gambiae

The spread of resistance to insecticides in the mosquito vectors of diseases such as malaria and dengue poses a threat to the effectiveness of control programmes, which rely largely on insecticide-based interventions. Monitoring the resistance status of mosquito populations is therefore essential, but obtaining direct phenotypic measurements of resistance is laborious and error-prone. In contrast, high-throughput genotyping offers the prospect of quick and repeatable estimates of resistance, while also allowing the genotypic markers of resistance to be tracked and studied. We developed a panel of 28 known or putative markers of resistance in the major malaria vector Anopheles gambiae, which we use to test the association of these markers with resistance and to study their geographic distribution. We screened resistance-phenotyped An. gambiae from populations from a wide swathe of Sub-Saharan Africa (Burkina Faso, Ghana, Democratic Republic of Congo (DRC) and Kenya), and found evidence of resistance association for four mutations, including a novel mutation in the detoxification gene Gste2 (Gste2-119V). We also identified a gene duplication in Gste2 which combines a resistance-associated mutant form of the gene with its wild-type counterpart, potentially alleviating the costs of resistance. Finally, we describe the distribution of the multiple evolutionary origins of kdr resistance, finding unprecedented levels of diversity in the DRC. This panel represents the first step towards developing a quantitative predictive genotypic model of insecticide resistance that can be used to screen An. gambiae populations and predict resistance status.

evolutionary biology↗