The effects of temephos, permethrin and malathion selection on the fitness and fecundity of Aedes aegypti

The recent scale‐up of insecticide use has led to the rapid spread of insecticide resistance (IR) in mosquito populations across the world. Previous work has suggested that IR mechanisms could influence mosquito life‐history traits, leading to alterations in fitness and key physiological functions. This study investigates to what extent mosquito fitness may be affected in a colony of Aedes aegypti after selection with temephos, permethrin or malathion insecticides. We measured immature development, sex ratio, adult longevity, energetic reserves under different rearing conditions and time points, ingested bloodmeal volume, mosquito size, male and female reproductive fitness and flight capability in the unexposed offspring of the three selected strains and unselected strain. We found that insecticide selection does have an impact on mosquito fitness traits in both male and female mosquitoes, with our temephos‐exposed strain showing the highest immature development rates, improved adult survival, larger females under crowded rearing and increased sperm number in males. In contrast, this strain showed the poorest reproductive success, demonstrating that insecticide selection leads to trade‐offs in life‐history traits, which have the potential to either enhance or limit disease transmission potential

Assessing the impact of the addition of pyriproxyfen on the durability of permethrin-treated bed nets in Burkina Faso: a compound-randomized controlled trial

Background Long-lasting insecticidal nets (LLINs) treated with pyrethroids are the foundation of malaria control in sub-Saharan Africa. Rising pyrethroid resistance in vectors, however, has driven the development of alternative net formulations. Here the durability of polyethylene nets with a novel combination of a pyrethroid, permethrin, and the insect juvenile hormone mimic, pyriproxyfen (PPF), compared to a standard permethrin LLIN, was assessed in rural Burkina Faso. Methods A compound-randomized controlled trial was completed in two villages. In one village 326 of the PPF-permethrin nets (Olyset Duo) and 327 standard LLINs (Olyset) were distributed to assess bioefficacy. In a second village, 170 PPF-permethrin nets and 376 LLINs were distributed to assess survivorship. Nets were followed at 6-monthly intervals for 3 years. Bioefficacy was assessed by exposing permethrin-susceptible and resistant Anopheles gambiae sensu lato mosquito strains to standard World Health Organization (WHO) cone and tunnel tests with impacts on fertility measured in the resistant strain. Insecticide content was measured using high-performance liquid chromatography. LLIN survivorship was recorded with a questionnaire and assessed by comparing the physical integrity using the proportionate hole index (pHI). Results The PPF-permethrin net met WHO bioefficacy criteria (≥ 80% mortality or ≥ 95% knockdown) for the first 18 months, compared to 6 months for the standard LLIN. Mean mosquito mortality for PPF-permethrin nets, across all time points, was 8.6% (CI 2.6–14.6%) higher than the standard LLIN. Fertility rates were reduced after PPF-permethrin net exposure at 1-month post distribution, but not later. Permethrin content of both types of nets remained within the target range of 20 g/kg ± 25% for 242/248 nets tested. The pyriproxyfen content of PPF-permethrin nets declined by 54%, from 10.4 g/kg (CI 10.2–10.6) to 4.7 g/kg (CI 3.5–6.0, p < 0.001) over 36 months. Net survivorship was poor, with only 13% of PPF-permethrin nets and 12% of LLINs still present in the original household after 36 months. There was no difference in the fabric integrity or survivorship between the two net types. Conclusion The PPF-permethrin net, Olyset Duo, met or exceeded the performance of the WHO-recommended standard LLIN (Olyset) in the current study but both net types failed the 3-year WHO bioefficacy criteria

Impacts of dual active-ingredient bed nets on the behavioural responses of pyrethroid resistant Anopheles gambiae determined by room-scale infrared video tracking.

BackgroundThe success of insecticide treated bed nets (ITNs) for malaria vector control in Africa relies on the behaviour of various species of Anopheles. Previous research has described mosquito behavioural alterations resulting from widespread ITN coverage, which could result in a decrease in net efficacy. Here, behaviours were compared including timings of net contact, willingness to refeed and longevity post-exposure to two next-generation nets, PermaNet® 3.0 (P3 net) and Interceptor® G2 (IG2 net) in comparison with a standard pyrethroid-only net (Olyset Net™ (OL net)) and an untreated net.MethodsSusceptible and resistant Anopheles gambiae mosquitoes were exposed to the nets with a human volunteer host in a room-scale assay. Mosquito movements were tracked for 2 h using an infrared video system, collecting flight trajectory, spatial position and net contact data. Post-assay, mosquitoes were monitored for a range of sublethal insecticide effects.ResultsMosquito net contact was focused predominantly on the roof for all four bed nets. A steep decay in activity was observed for both susceptible strains when P3 net and OL net were present and with IG2 net for one of the two susceptible strains. Total mosquito activity was higher around untreated nets than ITNs. There was no difference in total activity, the number, or duration, of net contact, between any mosquito strain, with similar behaviours recorded in susceptible and resistant strains at all ITNs. OL net, P3 net and IG2 net all killed over 90% of susceptible mosquitoes 24 h after exposure, but this effect was not seen with resistant mosquitoes where mortality ranged from 16 to 72%. All treated nets reduced the willingness of resistant strains to re-feed when offered blood 1-h post-exposure, with a more pronounced effect seen with P3 net and OL net than IG2 net.ConclusionThese are the first results to provide an in-depth description of the behaviour of susceptible and resistant Anopheles gambiae strains around next-generation bed nets using a room-scale tracking system to capture multiple behaviours. These results indicate that there is no major difference in behavioural responses between mosquito strains of differing pyrethroid susceptibility when exposed to these new ITNs under the experimental conditions used

The seasonal dynamics and biting behavior of potential Anopheles vectors of Plasmodium knowlesi in Palawan, Philippines.

BACKGROUND: A small number of human cases of the zoonotic malaria Plasmodium knowlesi have been reported in Palawan Island, the Philippines. Identification of potential vector species and their bionomics is crucial for understanding human exposure risk in this setting. Here, we combined longitudinal surveillance with a trap-evaluation study to address knowledge gaps about the ecology and potential for zoonotic spillover of this macaque malaria in Palawan Island. METHODS: The abundance, diversity and biting behavior of human-biting Anopheles mosquitoes were assessed through monthly outdoor human landing catches (HLC) in three ecotypes representing different land use (forest edge, forest and agricultural area) across 8 months. Additionally, the host preference and biting activity of potential Anopheles vectors were assessed through comparison of their abundance and capture time in traps baited with humans (HLC, human-baited electrocuting net-HEN) or macaques (monkey-baited trap-MBT, monkey-baited electrocuting net-MEN). All female Anopheles mosquitoes were tested for the presence of Plasmodium parasites by PCR. RESULTS: Previously incriminated vectors Anopheles balabacensis and An. flavirostris accounted for > 95% of anophelines caught in longitudinal surveillance. However, human biting densities were relatively low (An. balabacensis: 0.34-1.20 per night, An. flavirostris: 0-2 bites per night). Biting densities of An. balabacensis were highest in the forest edge, while An. flavirostris was most abundant in the agricultural area. The abundance of An. balabacensis and An. flavirostris was significantly higher in HLC than in MBT. None of the 357 female Anopheles mosquitoes tested for Plasmodium infection were positive. CONCLUSIONS: The relatively low density and lack of malaria infection in Anopheles mosquitoes sampled here indicates that exposure to P. knowlesi in this setting is considerably lower than in neighboring countries (i.e. Malaysia), where it is now the primary cause of malaria in humans. Although anophelines had lower abundance in MBTs than in HLCs, An. balabacensis and An. flavirostris were caught by both methods, suggesting they could act as bridge vectors between humans and macaques. These species bite primarily outdoors during the early evening, confirming that insecticide-treated nets are unlikely to provide protection against P. knowlesi vectors

The durability of long-lasting insecticidal nets treated with and without piperonyl butoxide: implications for bioefficacy and personal protection

Long-lasting Insecticidal nets (LLINs) are a fundamental component of malaria control strategies, yet they accumulate physical damage and lose insecticide over time. However, the impact of this deterioration on bioefficacy and bloodfeeding is poorly described. There is growing evidence that the operational lifespan of LLINs is less than the expected three years in some settings. Consequently, there is a need to assess the durability of LLIN products to determine the appropriate timescale of distribution. The emergence of pyrethroid-resistance in sub-Saharan Africa has motivated the development of LLIN designs that contain the synergist piperonyl butoxide to restore susceptibility. The aim of this study was to quantify the durability of LLINs with and without piperonyl butoxide in operational conditions. The nets assessed in this study were provided from collections performed as part of a randomised control trial to compare pyrethroid-only and pyrethroid-PBO nets. Each cluster received a pyrethroid-PBO net ( ‘Olyset Plus’ or ‘PermaNet 3.0’) or pyrethroid-only equivalent (‘Olyset Net’ or ‘PermaNet 2.0’). Samples were assessed at baseline, 12 months, and 25 months post distribution. The chemical content of pyrethroid and PBO of nets was assessed using high-performance liquid chromatography. The number, size, and location of holes on each net was assessed visually. Bioefficacy was assessed by exposing pyrethroid-resistant Anopheles to samples using WHO cone and wireball bioassays. To evaluate the impact of hole location on protective effect, behavioural experiments with free-flying pyrethroid-resistant Anopheles around human-occupied holed nets were conducted. Bloodfeeding success, 1hr knockdown, and 24hr mortality were compared for nets with no hole, hole in the top, or hole in the side. Pyrethroid content remained relatively stable across timepoints. However, the PBO content of both Olyset Plus and PermaNet 3.0 declined over the same period, falling by 55% (P<0.001) and 58% (p<0.001) respectively after 25 months. Both PBO nets were highly effective against pyrethroid-resistant An. gambiae when new but declined over time. After 25 months, 24hr mortality was 22.92% for Olyset Plus and 46.6% for PermaNet 3.0. There was a strong correlation between PBO content and mortality. There was no difference in any physical durability metric between any of the LLIN products evaluated, at any timepoint. In behavioural assays, holes on the top of the net had a much greatly risk of bloodfeeding compared to holes on the side (30.65% compared to 4.13%, P=0.021) after one hour. There was no difference in bloodfeeding success between Olyset Plus and Olyset Net (p=0.076). Very few bloodfed mosquitoes survived the assay with Olyset Plus, with 96.1% of all bloodfed mosquitoes dying after 24 hours despite very low morality for those that did not bloodfeed (<5%). Finally, when attempting to escape the net after bloodfeeding, mosquitoes were twice as likely to get out of a net with a hole on the top than on the side. These findings indicate that pyrethroid-PBO bed nets were highly effective against pyrethroid-resistant mosquitoes in Uganda when new but efficacy declined sharply over time. For both Olyset Plus and PermaNet 3.0, this rapid reduction in bioefficacy correlated with a steep decline in PBO content. Given that pyrethroid-PBO nets are becoming widespread, this finding is highly concerning and requires further investigation in other settings. Moreover, the rapid reduction in bioefficacy indicates a distribution cycle shorter than three years may be prudent. Physical integrity outcomes were very similar for the PBO nets and their pyrethroid-only equivalents. Current WHO durability assessment guidelines consider all holes equally when evaluating serviceability for use, yet here it was observed that holes on the top of the net were a 10x greatest risk for mosquito entry and bloodfeeding compared to the side. Consequently, guidelines for assessing survivability should be updated to appropriately weight holes on the top

Unmanned aerial vehicles for surveillance and control of vectors of malaria and other vector-borne diseases

Abstract The use of Unmanned Aerial Vehicles (UAVs) has expanded rapidly in ecological conservation and agriculture, with a growing literature describing their potential applications in global health efforts including vector control. Vector-borne diseases carry severe public health and economic impacts to over half of the global population yet conventional approaches to the surveillance and treatment of vector habitats is typically laborious and slow. The high mobility of UAVs allows them to reach remote areas that might otherwise be inaccessible to ground-based teams. Given the rapidly expanding examples of these tools in vector control programmes, there is a need to establish the current knowledge base of applications for UAVs in this context and assess the strengths and challenges compared to conventional methodologies. This review aims to summarize the currently available knowledge on the capabilities of UAVs in both malaria control and in vector control more broadly in cases where the technology could be readily adapted to malaria vectors. This review will cover the current use of UAVs in vector habitat surveillance and deployment of control payloads, in comparison with their existing conventional approaches. Finally, this review will highlight the logistical and regulatory challenges in scaling up the use of UAVs in malaria control programmes and highlight potential future developments. Graphical Abstrac

Unpacking WHO and CDC Bottle Bioassay Methods: A Comprehensive Literature Review and Protocol Analysis Revealing Key Outcome Predictors

Background Resistance monitoring is a key element in controlling vector-borne diseases. The World Health Organization (WHO) and Centres for Disease Control and Prevention (CDC) have each developed bottle bioassay methods for determining insecticide susceptibility in mosquito vectors which are used globally. Methods This study aimed to identify variations in bottle bioassay methodologies and assess the potential impact on the data that is generated. Our approach involved a systematic examination of existing literature and protocols from WHO and CDC, with a focus on the specifics of reported methodologies, variation between versions, and reported outcomes. Building on this, we experimentally evaluated the impact of several variables on bioassay results. Results Our literature review exposed a significant inconsistency in the how bioassay methods are reported, hindering reliable interpretation of data and the ability to compare results between studies. The experimental research provided further insight by specifically identifying two key factors that influence the outcomes of bioassays: mosquito dry weight and relative humidity (RH). This finding not only advances our comprehension of these assays but also underscores the importance of establishing precisely defined methodologies for resistance monitoring. The study also demonstrates the importance of controlling bioassay variables, noting the significant influence of wing length, as an indicator of mosquito size, on mortality rates in standardized bioassays. Conclusions Generating data with improved protocol consistency and precision will not only deepen our understanding of resistance patterns but also better inform vector control measures. We call for continued research and collaboration to refine and build consensus on bioassay techniques, to help bolster the global effort against vector-borne diseases like malaria

Elimination within reach: A cross-sectional study highlighting the factors that contribute to persistent lymphatic filariasis in eight communities in rural Ghana

Background Despite the progress achieved in scaling-up mass drug administration (MDA) for lymphatic filariasis (LF) in Ghana, communities with persistent LF still exist despite over 10 years of community treatment. To understand the reasons for persistence, we conducted a study to assess the status of disease elimination and understand the adherence to interventions including MDA and insecticide treated nets. Methodology and principal findings We conducted a parasitological and epidemiological cross-sectional study in adults from eight villages still under MDA in the Northern Region savannah and the coastal Western Region of the country. Prevalence of filarial antigen ranged 0 to 32.4% and in five villages the prevalence of night blood microfilaria (mf) was above 1%, ranging from 0 to 5.7%. Median mf density was 67 mf/ml (range: 10-3,560). LF antigen positivity was positively associated with male sex but negatively associated with participating in MDA the previous year. Male sex was also associated with a decreased probability of participating in MDA. A stochastic model (TRANSFIL) was used to assess the expected microfilaria prevalence under different MDA coverage scenarios using historical data on one community in the Western Region. In this example, the model simulations suggested that the slow decline in mf prevalence is what we would expect given high baseline prevalence and a high correlation between MDA adherence from year to year, despite high MDA coverage. Conclusions There is a need for an integrated quantitative and qualitative research approach to identify the variations in prevalence, associated risk factors and intervention coverage and use levels between and within regions and districts. Such knowledge will help target resources and enhance surveillance to the communities most at risk and to reach the 2020 LF elimination goals in Ghana