414 research outputs found
Landscape genetics of Anopheles gambiae in southern Ghana
No full textInsecticide application via indoor residual spraying (IRS) and long-lasting insecticide-treated bednets (LLIN) has been a key component in combating malaria in sub-Saharan Africa, with pyrethroids being the traditionally recommended insecticides. However, the resistance of Anopheles gambiae s.s. and An. coluzzii to pyrethroids is high and widespread, especially in West Africa, underpinned in part by high frequencies of the L1014F target-site mutation in the voltage-gated sodium channel (Vgsc). Carbamate (CB) and organophosphate (OP) resistance is generally lower but appears to be spreading via increasing frequencies of acetylcholinesterase (Ace-1) target site mutations involving the G119S polymorphism. Whilst Vgsc-1014F often nears fixation, Ace-1-119S is far more heterogeneous with complex copy number variant (CNV) dynamics. This study seeks to identify the determinants of Ace-1-119S spatial and temporal distribution and use population genetics to quantify the fine-scale population structure of An. gambiae s.s and An. coluzzii to understand how genetic barriers and gene flow may determine the current and future geographical spread.
The study across southern Ghana demonstrated that ecological zones and land-use activities are important determinants of Ace-1-119S and Vgsc-1014F distributions. The Vgsc-1014F is associated with rural, mining, and cash crop plantations, while Ace-1-119S is associated with urban agricultural activities. These human-influenced environmental factors are likely to influence selection for, and the spread of the insecticide resistance mutations. Interesting, whilst almost all past studies have shown that insecticidal mortality increased with mosquito age, this was not the case for pirimiphos-methyl. Indeed, mortality was well predicted by Ace-1 mutant type but not age, suggesting that age-dependent costs of resistance may be low, and more broadly that age-specific resistance is not a universal phenomenon and may depend on insecticide class and resistance mechanisms.
The study also showed that informative molecular markers such as Ace-1 can be used for sensitive temporal surveillance to track the changes in resistance in populations missed by standard diagnostic dose assays. In the focal area of Accra from which the time series of samples were collected, Ace-1-119S frequencies within An. gambiae s.s. and An. coluzzii appeared destined for fixation but deviated from this path in recent years. This resulted from the co-existence of homogeneous and heterogeneous Ace-1 duplications, with balancing of mutant polymorphisms likely a result of different costs and benefits of each. There was also evidence of shifting Ace-1 duplication type dynamics that are operating in the opposite direction in each species – presumably bringing each towards a common equilibrium.
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Finally, Anopheles gambiae s.s. and An. coluzzii sampled from 34 sites spanning the four ecological zones, and land-use types were genotyped using around 10,000 markers generated by low-coverage genome sequencing. Results showed a striking lack of close relatives among mosquitoes, despite larval sampling, suggesting that the strategy of collecting from multiple sites within (on average) a 3.0-km radius successfully yielded unrelated mosquitoes. There was low genetic differentiation and no population structure within both An. coluzzii and An. gambiae s.s. across southern Ghana. However, An. coluzzii showed isolation by distance at a local sampling scale, suggesting there is distance-limited dispersal, and that patterns reflect contemporary gene flow. In An. gambiae s.s, no isolation by distance was detectable, even at a smaller geographical distance of separation suggesting the implication of historical signals for the observed no population structure. The results also showed that distance is not the primary cause of Ace-1 differentiation, but rather habitat differentiation which may correlate with distance. The findings of this study have given insight into phenotypic resistance of primary Anopheles malaria vectors to CB and particularly OP and how underlying target-site resistance mechanisms may be selected by environmental factors to modulate resistance and its spread. This information provides guidelines for vector control and resistance management
Long-term trends in Anopheles gambiae insecticide resistance in Côte d'Ivoire
No full textMalaria control is heavily dependent on the use of insecticides that target adult mosquito vectors via insecticide treated nets (ITNs) or indoor residual spraying (IRS). Four classes of insecticide are approved for IRS but only pyrethroids are available for ITNs. The rapid rise in insecticide resistance in African malaria vectors has raised alarms about the sustainability of existing malaria control activities. This problem might be particularly acute in Côte d¿Ivoire where resistance to all four insecticide classes has recently been recorded. Here we investigate temporal trends in insecticide resistance across the ecological zones of Côte d¿Ivoire to determine whether apparent pan-African patterns of increasing resistance are detectable and consistent across insecticides and areas.MethodsWe combined data on insecticide resistance from a literature review, and bioassays conducted on field-caught Anopheles gambiae mosquitoes for the four WHO-approved insecticide classes for ITN/IRS. The data were then mapped using Geographical Information Systems (GIS) and the IR mapper tool to provide spatial and temporal distribution data on insecticide resistance in An. gambiae sensu lato from Côte d¿Ivoire between 1993 and 2014.ResultsBioassay mortality decreased over time for all insecticide classes, though with significant spatiotemporal variation, such that stronger declines were observed in the southern ecological zone for DDT and pyrethroids than in the central zone, but with an apparently opposite effect for the carbamate and organophosphate. Variation in relative abundance of the molecular forms, coupled with dramatic increase in kdr 1014F frequency in M forms (An. coluzzii) seems likely to be a contributory factor to these patterns. Although records of resistance across insecticide classes have become more common, the number of classes tested in studies has also increased, precluding a conclusion that multiple resistance has also increased.ConclusionOur analyses attempted synthesis of 22 years of bioassay data from Côte d¿Ivoire, and despite a number of caveats and potentially confounding variables, suggest significant but spatially-variable temporal trends in insecticide resistance. In the light of such spatio-temporal dynamics, regular, systematic and spatially-expanded monitoring is warranted to provide accurate information on insecticide resistance for control programme management
BEHAVIOURAL AND PHYSIOLOGICAL INSECTICIDE RESISTANCE OF THE DENGUE VECTOR AEDES AEGYPTI IN THE KINGDOM OF SAUDI ARABIA
No full textEffects of run-up velocity on performance, kinematics, and energy exchanges in the pole vault
No full textCopyright @ 2012 The Authors. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and 85 reproduction in any medium, provided the original author and source are credited. The article was made available through the Brunel University Open Access Publishing Fund.This study examined the effect of run-up velocity on the peak height achieved by the athlete in the pole vault and on the corresponding changes in the athlete's kinematics and energy exchanges. Seventeen jumps by an experienced male pole vaulter were video recorded in the sagittal plane and a wide range of run-up velocities (4.5-8.5 m/s) was obtained by setting the length of the athlete's run-up (2-16 steps). A selection of performance variables, kinematic variables, energy variables, and pole variables were calculated from the digitized video data. We found that the athlete's peak height increased linearly at a rate of 0.54 m per 1 m/s increase in run-up velocity and this increase was achieved through a combination of a greater grip height and a greater push height. At the athlete's competition run-up velocity (8.4 m/s) about one third of the rate of increase in peak height arose from an increase in grip height and about two thirds arose from an increase in push height. Across the range of run-up velocities examined here the athlete always performed the basic actions of running, planting, jumping, and inverting on the pole. However, he made minor systematic changes to his jumping kinematics, vaulting kinematics, and selection of pole characteristics as the run-up velocity increased. The increase in run-up velocity and changes in the athlete's vaulting kinematics resulted in substantial changes to the magnitudes of the energy exchanges during the vault. A faster run-up produced a greater loss of energy during the take-off, but this loss was not sufficient to negate the increase in run-up velocity and the increase in work done by the athlete during the pole support phase. The athlete therefore always had a net energy gain during the vault. However, the magnitude of this gain decreased slightly as run-up velocity increased
Development and field-evaluation of vector surveillance tools for identifying arbovirus circulation, mosquito species and insecticide resistance
No full textVector surveillance builds the foundation for effective planning of mosquito-borne disease prevention. Data, on the species composition of vector populations alongside their pathogen infection and insecticide resistance status, are crucial for informed decisions on vector control strategies. The overarching goal of this PhD thesis was to contribute to novel and improved vector surveillance tools for the characterisation of mosquito field populations.
Continental Europe is facing an emerging threat from mosquito-transmitted viral diseases as several locally transmitted recent outbreaks have demonstrated. The main obstacles for launching large-scale arbovirus surveillance in Switzerland are the laborious processing of thousands of mosquitoes, the need for a constant cold chain to preserve viral RNA in infected specimens and the high costs associated with these factors. An alternative approach is using honey-baited nucleic acid preserving cards (FTA cards) to sample saliva from potentially infectious mosquitoes that feed on the sugar bait. During my PhD, I evaluated honey-baited FTA cards as an innovative method for detecting arbovirus circulation in mosquito field populations (Part I).
The importance of early warning through mosquito surveillance is equally applicable in the African context, where the raise and rapid spread of insecticide resistance threatens the success of malaria control programmes. Molecular diagnostics is increasingly important for effective insecticide resistance management strategies. Currently, several highly complex protocols for detecting molecular resistance mechanisms in malaria vectors exist. To facilitate the use of molecular diagnostics in endemic countries, I was engaged in the Diagnosis Management Communication-Malaria Vector Control (DMC-MALVEC) project that aims to develop an automated sample-to-answer diagnostic tool (LabDisk) to screen Anopheles gambiae s.l. mosquitoes simultaneously for pathogen infection and insecticide resistance markers as well as their species composition (Part II).
Part I – Surveillance of arboviruses using honey-baited FTA cards
The objective of Chapter 2 was to evaluate whether honey-baited FTA cards, in combination with an efficient mosquito trap, are a sufficiently sensitive tool to detect virus circulation in an area of low arbovirus prevalence. In a field trial in southern Switzerland, we measured the efficacy of three mosquito traps that were equipped with honey-baited FTA cards, and we found that the Box gravid trap caught 11× more target specimens than the BG-GAT and the BG-Sentinel 2 trap. Screening a total of 507 Aedes and 500 Culex females as well as 240 FTA cards for the presence of arboviruses, we detected Usutu virus in a pool of six Culex pipiens/torrentium mosquitoes and on the FTA card from the same trap. In conclusion, we found honey-baited FTA cards in combination with the Box gravid trap to be a highly sensitive early-warning tool for mosquito-borne virus circulation.
Part II – Surveillance of malaria vectors and insecticide resistance
The second part of this PhD thesis aimed at developing and optimising (RT-)qPCR assays that meet the technical requirements of the Anopheles gambiae LabDisk and the associated reader. The assays were then validated using field-collected specimens and compared with transcriptome sequencing with a particular focus on detecting genes involved in insecticide resistance.
In Chapter 3, we developed a method for estimating the allele frequency of knockdown resistance (kdr) mutations in a pool of ten Anopheles mosquitoes. Linear regression models can predict the allelic frequency in pooled specimens as a function of the ΔCt values (Ct mutant – Ct wild type probe) with comparable accuracy to genotyping individuals. In Chapter 4, we developed one-step multiplex RT-qPCR assays de novo to quantify expression levels of seven cytochrome P450-dependent monooxygenase (P450), including CYP6M2, CYP6P4, CYP6P3, CYP6P1, CYP6Z1, CYP9K1 and CYP4G16, and the glutathione S-transferase GSTE2. All (RT-)qPCR assays for detecting target-site (Chapter 3) and metabolic (Chapter 4) insecticide resistance are efficient, sensitive, specific and reproducible using the same chemistry and thermal cycle parameters. This qualifies them for integration into the sophisticated Anopheles gambiae LabDisk or into simpler malaria vector diagnostic kits with lyophilised reagents that can be used on conventional qPCR instruments.
In Chapter 5, we successfully applied the new (RT-)qPCR assays on multi-insecticide resistant malaria vectors collected in southern Côte d’Ivoire. In this study, we found that highly pyrethroid resistant Anopheles coluzzii from Tiassalé were still fully susceptible to malathion, despite high frequencies of the acetylcholinesterase mutation Ace1-G280S that would typically confer malathion resistance. By sequencing the transcriptomes of individual mosquitoes, we found numerous P450s that were highly overexpressed. This could indicate negative cross-resistance caused by overexpression of pyrethroid-detoxifying cytochrome P450s that may activate the pro-insecticide malathion, thereby increasing malathion susceptibility. In addition to the P450s, we found several overexpressed carboxylesterases, glutathione S-transferases, and other genes putatively involved in insecticide resistance and highlighted several candidates for functional validation.
In conclusion, my PhD projects contributed to the development, evaluation and implementation of innovative, flexible and reliable vector surveillance tools that describe relevant characteristics of mosquito field populations. In particular, I contributed (I) to the implementation of honey-baited FTA cards as a novel arbovirus surveillance tool in Switzerland; and (II) to improved malaria vector diagnostics with novel protocols for more effective and efficient surveillance of molecular insecticide resistance mechanisms
Reverse supply chains
No full textA Circular Economy Handbook for Business and Supply Chains is an easily digestible and comprehensive handbook that provides a clear guide to the circular economy, helping the reader create future-fit, sustainable strategies. Real examples across a range of market sectors help businesses, students and policymakers understand the theory and fast-developing practice of the circular economy. To help the reader generate ideas, A Circular Economy Handbook for Business and Supply Chains provides a holistic framework for the design and supply chain and supporting business models, and includes tools the reader can use to get started.
Whilst growing global consumption presents fantastic business opportunities, our current linear systems (take some materials, make a product, use it and then throw it away) are not fit for purpose. The circular economy unlocks this problem by decoupling resources from consumption. Engaged businesses are re-thinking product design, material choices, business models and supply chains. A Circular Economy Handbook for Business and Supply Chains is a must-read for anyone who wants to apply the circular economy today. Online resources now available: PowerPoint slides of figures and tables from every chapter created by the author
X-chromosome localized recombination hotspots undermine existing molecular diagnosis of Anopheles gambiae and An. coluzzii under high hybridization
No full textThe last bastion? X chromosome genotyping of Anopheles gambiae species pair males from a hybrid zone reveals complex recombination within the major candidate 'genomic island of speciation'
No full textSpeciation with gene flow may be aided by reduced recombination helping to build linkage between genes involved in the early stages of reproductive isolation. Reduced recombination on chromosome X has been implicated in speciation within the Anopheles gambiae complex, species of which represent the major Afrotropical malaria vectors. The most recently diverged, morphologically indistinguishable, species pair, A. gambiae and Anopheles coluzzii, ubiquitously displays a 'genomic island of divergence' spanning over 4 Mb from chromosome X centromere, which represents a particularly promising candidate region for reproductive isolation genes, in addition to containing the diagnostic markers used to distinguish the species. Very low recombination makes the island intractable for experimental recombination studies, but an extreme hybrid zone in Guinea Bissau offers the opportunity for natural investigation of X-island recombination. SNP analysis of chromosome X hemizygous males revealed: (i) strong divergence in the X-island despite a lack of autosomal divergence; (ii) individuals with multiple-recombinant genotypes, including likely double crossovers and localized gene conversion; (iii) recombination-driven discontinuity both within and between the molecular species markers, suggesting that the utility of the diagnostics is undermined under high hybridization. The largely, but incompletely protected nature of the X centromeric genomic island is consistent with a primary candidate area for accumulation of adaptive variants driving speciation with gene flow, while permitting some selective shuffling and removal of genetic variation
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