Permethrin-Treated Clothing as Protection against the Dengue Vector, Aedes aegypti: Extent and Duration of Protection.

INTRODUCTION: Dengue transmission by the mosquito vector, Aedes aegypti, occurs indoors and outdoors during the day. Personal protection of individuals, particularly when outside, is challenging. Here we assess the efficacy and durability of different types of insecticide-treated clothing on laboratory-reared Ae. aegypti. METHODS: Standardised World Health Organisation Pesticide Evaluation Scheme (WHOPES) cone tests and arm-in-cage assays were used to assess knockdown (KD) and mortality of Ae. aegypti tested against factory-treated fabric, home-dipped fabric and microencapsulated fabric. Based on the testing of these three different treatment types, the most protective was selected for further analysis using arm-in cage assays with the effect of washing, ultra-violet light, and ironing investigated using high pressure liquid chromatography. RESULTS: Efficacy varied between the microencapsulated and factory dipped fabrics in cone testing. Factory-dipped clothing showed the greatest effect on KD (3 min 38.1%; 1 hour 96.5%) and mortality (97.1%) with no significant difference between this and the factory dipped school uniforms. Factory-dipped clothing was therefore selected for further testing. Factory dipped clothing provided 59% (95% CI = 49.2%- 66.9%) reduction in landing and a 100% reduction in biting in arm-in-cage tests. Washing duration and technique had a significant effect, with insecticidal longevity shown to be greater with machine washing (LW50 = 33.4) compared to simulated hand washing (LW50 = 17.6). Ironing significantly reduced permethrin content after 1 week of simulated use, with a 96.7% decrease after 3 months although UV exposure did not reduce permethrin content within clothing significantly after 3 months simulated use. CONCLUSION: Permethrin-treated clothing may be a promising intervention in reducing dengue transmission. However, our findings also suggest that clothing may provide only short-term protection due to the effect of washing and ironing, highlighting the need for improved fabric treatment techniques

Personal Protection of Permethrin-Treated Clothing against Aedes aegypti, the Vector of Dengue and Zika Virus, in the Laboratory.

BACKGROUND: The dengue and Zika viruses are primarily transmitted by Aedes aegypti mosquitoes, which are most active during day light hours and feed both in and outside of the household. Personal protection technologies such as insecticide-treated clothing could provide individual protection. Here we assessed the efficacy of permethrin-treated clothing on personal protection in the laboratory. METHODS: The effect of washing on treated clothing, skin coverage and protection against resistant and susceptible Ae. aegypti was assessed using modified WHO arm-in-cage assays. Coverage was further assessed using free-flight room tests to investigate the protective efficacy of unwashed factory-dipped permethrin-treated clothing. Clothing was worn as full coverage (long sleeves and trousers) and partial coverage (short sleeves and shorts). Residual permethrin on the skin and its effect on mosquitoes was measured using modified WHO cone assays and quantified using high-pressure liquid chromatography (HPLC) analysis. RESULTS: In the arm-in-cage assays, unwashed clothing reduced landing by 58.9% (95% CI 49.2-66.9) and biting by 28.5% (95% CI 22.5-34.0), but reduced to 18.5% (95% CI 14.7-22.3) and 11.1% (95% CI 8.5-13.8) respectively after 10 washes. Landing and biting for resistant and susceptible strains was not significantly different (p80% one hour after wearing treated clothing. CONCLUSION: Whilst partially covering the body with permethrin-treated clothing provided some protection against biting, wearing treated clothing with long sleeves and trousers provided the highest form of protection. Washing treated clothing dramatically reduced protection provided. Permethrin-treated clothing could provide protection to individuals from Ae. aegypti that show permethrin resistance. Additionally, it could continue to provide protection even after the clothing has been worn. Field trials are urgently needed to determine whether clothing can protect against dengue and Zika

Evidence of extrinsic factors dominating intrinsic blood host preferences of major African malaria vectors.

One of the key determinants of a haematophagous vector's capacity to transmit pathogens is its selection of which host to secure a blood meal from. This choice is influenced by both intrinsic (genetic) and extrinsic (environmental) factors, but little is known of their relative contributions. Blood fed Anopheles mosquitoes were collected from a malaria endemic village in Ghana. Collections were conducted across a range of different host availabilities and from both indoor and outdoor locations. These environmental factors were shown to impact dramatically the host choice of caught malaria vectors: mosquitoes caught indoors were ten-fold more likely to have sourced their blood meal from humans; and a halving in odds of being human-fed was found for mosquitoes caught only 25 m from the centre of the village. For the first time, we demonstrate that anthropophagy was better explained by extrinsic factors (namely, local host availability and indoor/outdoor trapping location) than intrinsic factors (namely, the (sibling) species of the mosquito caught) (respective Akaike information criterion estimates: 243.0 versus 359.8). Instead of characterizing biting behaviour on a taxonomic level, we illustrate the importance of assessing local entomology. Accounting for this behavioural plasticity is important, both in terms of measuring effectiveness of control programmes and in informing optimal disease control strategies

Using the human blood index to investigate host biting plasticity: a systematic review and meta-regression of the three major African malaria vectors.

The proportion of mosquito blood-meals that are of human origin, referred to as the 'human blood index' or HBI, is a key determinant of malaria transmission. A systematic review was conducted followed by meta-regression of the HBI for the major African malaria vectors. Evidence is presented for higher HBI among Anopheles gambiae (M/S forms and Anopheles coluzzii/An. gambiae sensu stricto are not distinguished for most studies and, therefore, combined) as well as Anopheles funestus when compared with Anopheles arabiensis (prevalence odds ratio adjusted for collection location [i.e. indoor or outdoor]: 1.62; 95% CI 1.09-2.42; 1.84; 95% CI 1.35-2.52, respectively). This finding is in keeping with the entomological literature which describes An. arabiensis to be more zoophagic than the other major African vectors. However, analysis also revealed that HBI was more associated with location of mosquito captures (R = 0.29) than with mosquito (sibling) species (R = 0.11). These findings call into question the appropriateness of current methods of assessing host preferences among disease vectors and have important implications for strategizing vector control

Clinical utilisation of implantable loop recorders in adults with Fabry disease-a multi-centre snapshot study

Fabry disease (FD) is an X-linked deficiency of alpha-galactosidase-A, leading to lysosomal storage of sphingolipids in multiple organs. Myocardial accumulation contributes to arrhythmia and sudden death, the most common cause of FD mortality. Therefore, there is a need for risk stratification and prediction to target device therapy. Implantable loop recorders (ILRs) allow for continual rhythm monitoring for up to 3 years. Here, we performed a retrospective study to evaluate current ILR utilisation in FD and quantify the burden of arrhythmia that was detected, which resulted in a modification of therapy. This was a snapshot assessment of 915 patients with FD across three specialist centres in England during the period between 1 January 2000 and 1 September 2022. In total, 22 (2.4%) patients underwent clinically indicated ILR implantation. The mean implantation age was 50 years and 13 (59%) patients were female. Following implantation, nine (41%) patients underwent arrhythmia detection, requiring intervention (six on ILR and three post-ILR battery depletion). Three patients experienced sustained atrial high-rate episodes and were started on anticoagulation. Three had non-sustained tachyarrhythmia and were started on beta blockers. Post-ILR battery depletion, one suffered complete heart block and two had sustained ventricular tachycardia, all requiring device therapy. Those with arrhythmia had a shorter PR interval on electrocardiography. This study demonstrates that ILR implantation in FD uncovers a high burden of arrhythmia. ILRs are likely to be underutilised in this pro-arrhythmic cohort, perhaps restricted to those with advanced FD cardiomyopathy. Following battery depletion in three patients as mentioned above, greater vigilance and arrhythmia surveillance are advised for those experiencing major arrhythmic events post-ILR monitoring. Further work is required to establish who would benefit most from implantation.</p

The relationship between insecticide resistance, mosquito age and malaria prevalence in Anopheles gambiae s.l. from Guinea.

Insecticide resistance across sub-Saharan Africa may impact the continued effectiveness of malaria vector control. We investigated the association between carbamate and pyrethroid resistance with Anopheles gambiae s.l. parity, Plasmodium falciparum infection, and molecular insecticide resistance mechanisms in Guinea. Pyrethroid resistance was intense, with field populations surviving ten times the insecticidal concentration required to kill susceptible individuals. The L1014F kdr-N1575Y haplotype and I1527T mutation were significantly associated with mosquito survival following permethrin exposure (Prevalence Ratio; PR = 1.92, CI = 1.09-3.37 and PR = 2.80, CI = 1.03-7.64, respectively). Partial restoration of pyrethroid susceptibility following synergist pre-exposure suggests a role for mixed-function oxidases. Carbamate resistance was lower and significantly associated with the G119S Ace-1 mutation. Oocyst rates were 6.8% and 4.2% among resistant and susceptible mosquitoes, respectively; survivors of bendiocarb exposure were significantly more likely to be infected. Pyrethroid resistant mosquitoes had significantly lower parity rates than their susceptible counterparts (PR = 1.15, CI = 1.10-1.21). Our findings emphasize the need for additional studies directly assessing the influence of insecticide resistance on mosquito fitness

Investigating the blood-host plasticity and dispersal of Anopheles coluzzii using a novel field-based methodology.

BACKGROUND: The biting behaviour and dispersal of insect vectors in the field underlies the transmission of many diseases. Here, a novel collection methodology coupled with the molecular analysis of blood-meal sources and digestion rates is introduced with the aim of aiding the understanding of two critical and relatively understudied mosquito behaviours: plasticity in blood-host choice and vector dispersal. RESULTS: A collection strategy utilising a transect of mosquito traps placed at 50 m intervals allowed the collection of blood-fed Anopheles coluzzii from a malaria-endemic village of southern Ghana where human host availability ranged from zero (a cattle pen), increasing until humans were the dominant host choice (the middle of the village). Blood-meal analysis using PCR showed statistically significant variation in blood-meal origins for mosquitoes collected across the 250 m transect: with decreasing trend in Bovine Blood Index (OR = 0.60 95% CI: 0.49-0.73, P < 0.01) and correspondingly, an increasing trend in Human Blood Index (OR = 1.50 95% CI: 1.05-2.16, P = 0.028) as the transect approached the village. Using qPCR, the host DNA remaining in the blood meal was quantified for field-caught mosquitoes and calibrated according to timed blood digestion in colony mosquitoes. Time since blood meal was consumed and the corresponding distance the vector was caught from its blood-host allowed the estimation of An. coluzzii dispersal rates. Within 7 hours of feeding, mosquitoes typically remained within 50 m of their blood-host but at 60 hours they had dispersed up to 250 m. CONCLUSIONS: Using this methodology the remarkably small spatial scale at which An. coluzzii blood-host choice can change was demonstrated. In addition, conducting qPCR on host blood from field-caught mosquitoes and calibrating with timed experiments with colonised mosquitoes presents a novel methodology for investigating the dispersal behaviour of vectors. Future adaptations to this novel method to make it broadly applicable to other types of setting are also discussed

Using the human blood index to investigate host biting plasticity: a systematic review and meta-regression of the three major African malaria vectors

Background: The proportion of mosquito blood-meals that are of human origin, referred to as the ‘human blood index’ or HBI, is a key determinant of malaria transmission. Methods: A systematic review was conducted followed by meta-regression of the HBI for the major African malaria vectors. Results: Evidence is presented for higher HBI among Anopheles gambiae (M/S forms and Anopheles coluzzii/An. gambiae sensu stricto are not distinguished for most studies and, therefore, combined) as well as Anopheles funestus when compared with Anopheles arabiensis (prevalence odds ratio adjusted for collection location [i.e. indoor or outdoor]: 1.62; 95% CI 1.09–2.42; 1.84; 95% CI 1.35–2.52, respectively). This fnding is in keeping with the entomological literature which describes An. arabiensis to be more zoophagic than the other major African vectors. However, analysis also revealed that HBI was more associated with location of mosquito captures (R2=0.29) than with mosquito (sibling) species (R2=0.11). Conclusions: These fndings call into question the appropriateness of current methods of assessing host preferences among disease vectors and have important implications for strategizing vector control.JO has an MRC London Intercollegiate Doctoral Training Partnership Student‑ ship. TW and CLJ are funded through a Wellcome Trust/Royal Society Sir Henry Dale Fellowship (101285/Z/13/Z) awarded to TW. LY received funds from a Royal Society Research Project (RSG\R1\180203

Genetic and microbial diversity of the invasive mosquito vector species <i>Culex tritaeniorhynchus</i> across its extensive inter-continental geographic range

AbstractCulex (Cx.) tritaeniorhynchus is a mosquito species with an extensive and expanding inter-continental geographic distribution, currently reported in over 50 countries, across Asia, Africa, the Middle East, Europe and now Australia. It is an important vector of medical and veterinary concern, capable of transmitting multiple arboviruses which cause significant morbidity and mortality in human and animal populations. In regions endemic for Japanese encephalitis virus (JEV) in Asia, Cx. tritaeniorhynchus is considered the major vector and this species has also been shown to contribute to the transmission of several other significant zoonotic arboviruses, including Rift Valley fever virus and West Nile virus.Significant variation in vectorial capacity can occur between different vector populations. Obtaining knowledge of a species from across its geographic range is crucial to understanding its significance for pathogen transmission across diverse environments and localities. Vectorial capacity can be influenced by factors including the mosquito genetic background, composition of the microbiota associated with the mosquito and the co-infection of human or animal pathogens. In addition to enhancing information on vector surveillance and potential risks for pathogen transmission, determining the genetic and microbial diversity of distinct populations of a vector species is also critical for the development and application of effective control strategies.In this study, multiple geographically dispersed populations of Cx. tritaeniorhynchus from countries within Europe, Africa, Eurasia and Asia were sampled. Molecular analysis demonstrated a high level of genetic and microbial diversity within and between populations, including genetic divergence in the mosquito CO1 gene, as well as diverse microbiomes identified by 16S rRNA gene amplicon sequencing. Evidence for the detection of the endosymbiotic bacteria Wolbachia in some populations was confirmed using Wolbachia-specific PCR detection and sequencing of Wolbachia MLST genes; in addition to PCR-based detection of insect-specific viruses. Laboratory vector competence showed Cx. tritaeniorhynchus from a Greek population are likely to be competent vectors of JEV. This study expands understanding of the diversity of Cx. tritaeniorhynchus across its inter-continental range, highlights the need for a greater focus on this invasive vector species and helps to inform potential future directions for development of vector control strategies.</jats:p

High-throughput barcoding method for the genetic surveillance of insecticide resistance and species identification in Anopheles gambiae complex malaria vectors.

Surveillance of malaria vector species and the monitoring of insecticide resistance are essential to inform malaria control strategies and support the reduction of infections and disease. Genetic barcoding of mosquitoes is a useful tool to assist the high-throughput surveillance of insecticide resistance, discriminate between sibling species and to detect the presence of Plasmodium infections. In this study, we combined multiplex PCR, custom designed dual indexing, and Illumina next generation sequencing for high throughput single nucleotide polymorphism (SNP)-profiling of four species from the Anopheles (An.) gambiae complex (An. gambiae sensu stricto, An. coluzzii, An. arabiensis and An. melas). By amplifying and sequencing only 14 genetic fragments (500 bp each), we were able to simultaneously detect Plasmodium infection; insecticide resistance-conferring SNPs in ace1, gste2, vgsc and rdl genes; the partial sequences of nuclear ribosomal internal transcribed spacers (ITS1 and ITS2) and intergenic spacers (IGS), Short INterspersed Elements (SINE), as well as mitochondrial genes (cox1 and nd4) for species identification and genetic diversity. Using this amplicon sequencing approach with the four selected An. gambiae complex species, we identified a total of 15 non-synonymous mutations in the insecticide target genes, including previously described mutations associated with resistance and two new mutations (F1525L in vgsc and D148E in gste2). Overall, we present a reliable and cost-effective high-throughput panel for surveillance of An. gambiae complex mosquitoes in malaria endemic regions