Integrated Vector Management Programmes Research Articles

Malaria’s molecular dance: Mechanism, therapies, and emerging insights

Malaria, caused by Plasmodium parasites and transmitted through Anopheles mosquitoes, remains a formidable global health challenge. This abstract provides an overview of the intricate molecular mechanisms underlying malaria pathogenesis, explores current therapeutic approaches, and highlights emerging insights that may shape future strategies for malaria control. The intricate dance between Plasmodium parasites and their human hosts begins with the mosquito’s bite, leading to the invasion of erythrocytes by Plasmodium species. We delve into the molecular mechanisms governing parasite entry and subsequent replication within host cells, shedding light on key factors such as erythrocyte surface receptors and parasite-encoded proteins critical to invasion and survival. While malaria treatment has relied heavily on antimalarial drugs, the emergence of drug resistance necessitates ongoing exploration of novel therapeutic strategies. This abstract reviews current antimalarial drug classes, their mechanisms of action, and the challenges posed by drug resistance. We also highlight promising drug candidates and innovative approaches in the pipeline, including the use of advanced molecular techniques and immunotherapies. Emerging insights from genomics, proteomics, and transcriptomics have deepened our understanding of Plasmodium biology and host-parasite interactions. We discuss the potential of these omics approaches in identifying new drug targets, understanding drug resistance mechanisms, and developing vaccines. Additionally, we examine the role of human genetics in influencing susceptibility to malaria and response to treatment. Vector control remains a critical component of malaria prevention. We touch upon emerging strategies, such as genetically modified mosquitoes and novel insecticides, in the context of integrated vector management programs. Finally, we emphasize the importance of a multifaceted approach to malaria control, combining advances in molecular biology, drug development, vector control, and public health interventions.

The effect of attractive toxic sugar bait on the Asian tiger mosquito, Aedes albopictus (Diptera: Culicidae) in community farms in Northern Taiwan

Attractive toxic sugar baits (ATSBs) lure mosquitoes to feed on the baits and subsequently killed them. We investigated the effects of a boric acid–containing ATSB on the population of Aedes albopictus at 48 h exposure and assessed the field effectiveness on this ATSB on two types of community farms in New Taipei City, Taiwan, including isolated ATSB farms and nonisolated ATSB farms. The result showed that mosquitoes exposed to the ATSB solution for 48 h were killed within 7 d under laboratory conditions. Exposure of female and male mosquitoes to ATSB resulted in mean survival times ranging from 52 to 62 h and 30 to 48 h, respectively. For field efficacy test, on isolated ATSB farms, a significant reduction of ovitrap density index (ODI) up to 24 % was noted after the replacement frequency was increased to every 2 weeks. However, the intervention efficacy on nonisolated ATSB farms had mixed results. The ODI significantly reduced by 21.4 % and 6.9 % on the nonisolated ATSB Chongmin and Nanjing farms, respectively, when bait replacement was done every 2 weeks instead of every 3 weeks. By contrast, the ODI on the nonisolated ATSB Yongchang farms increased significantly, irrespectively of the bait replacement frequency. Nevertheless, the total number of eggs trapped on all ATSB farms exhibited a concave curve pattern; while the mosquito population on non-ATSB control farms continued to increase over time. In conclusion, deploying simple ATSB stations containing boric acid is a practical approach for integrated vector management programs.

Effect of non-human hosts on the human biting rate of primary and secondary malaria vectors in Tanzania

BackgroundMalaria vectors vary in feeding preference depending on their innate behaviour, host availability and abundance. Host preference and human biting rate in malaria vectors are key factors in establishing zooprophylaxis and zoopotentiation. This study aimed at assessing the impact of non-human hosts in close proximity to humans on the human biting rate of primary and secondary malaria vectors, with varying host preferences.MethodsThe effect of the presence of non-human hosts in close proximity to the human host on the mean catches per person per night, as a proxy for mosquito biting rate, was measured using mosquito-electrocuting traps (METs), in Sagamaganga, Kilombero Valley, Tanzania. Two experiments were designed: (1) a human versus a calf, each enclosed in a MET, and (2) a human surrounded by three calves versus a human alone, with each human volunteer enclosed individually in a MET spaced 10 m apart. Each experiment was conducted on alternate days and lasted for 36 nights per experiment. During each experiment, the positions of hosts were exchanged daily (except the human in experiment 2). All anopheline mosquitoes caught were assayed for Plasmodium sporozoites using enzyme-linked immunosorbent assay.ResultsA total of 20,574 mosquitoes were captured and identified during the study, of which 3608 were anophelines (84.4% primary and 15.6% secondary malaria vectors) and 17,146 were culicines. In experiment 1, the primary malaria vector, Anopheles arabiensis, along with Culex spp. demonstrated a preference for cattle, while the primary vectors, Anopheles funestus, preferred humans. In experiment 2, both primary vectors, An. arabiensis and An. funestus, as well as the secondary vector Anopheles rivolurum, demonstrated behaviours amenable to zooprophylaxis, whereas Culex spp. increased their attraction to humans in the presence of nearby cattle. All anopheline mosquitoes tested negative for sporozoites.ConclusionsThe findings of this study provide support for the zooprophylaxis model for malaria vectors present in the Kilombero Valley, and for the zoopotentiation model, as it pertains to the Culex spp. in the region. However, the factors regulating zooprophylaxis and zoopotentiation are complex, with different species-dependent mechanisms regulating these behaviours, that need to be considered when designing integrated vector management programmes.

Laboratory scale evaluation of the feasibility of locally found bladderworts as biological agents to control dengue vector, Aedes aegypti in Sri Lanka

BackgroundThe carnivorous genus Utricularia also includes aquatic species that have the potential to trap a wide range of prey, leading its death due to anoxia. However, the effectiveness of such an approach with carnivorous plants for vector control has not been evaluated in Sri Lanka.MethodsEarly instar (i & ii) and late instar (iii & iv) larvae of Aedes aegypti were exposed to locally found bladderwort (U. aurea Lour and Utricularia sp.). The experimental design was set with 10 larvae (both early and late instars separately) in 250 mL of water with bladderworts containing approximately 100 bladders in plant segments of both species, separately. Each treatment and control were repeated 50 times. The survival status of larvae was recorded daily until death or adult emergence. The larvae found whole or partially inside the bladders were attributed to direct predation. The Cox-regression model and Mantel-Cox log rank test were carried out to assess the survival probabilities of larvae in the presence of two bladderworts separately.ResultsThe highest predation was observed when using early instar larvae in both U. aurea (97.8%) and Utricularia sp. (83.8%). The mortality caused due to predation by U. aurea was observed to be significantly higher according to the Mantel-Cox log-rank test (HR = 60.71, CI; 5.69–999.25, P = 0.004). The mortality rates of late instar stages of Ae. aegypti were observed to be lower in both U. aurea (82.6%) and Utricularia sp. (74.8%). Overall, the highest predation efficacy was detected from U. aurea (HR = 45.02; CI: 5.96–850.51, P = 0.017) even in late instar stages. The results suggested the cumulative predation in both plants on Ae. aegypti larvae was > 72%.ConclusionsUtricularia aurea is a competent predator of Ae. aegypti larvae. Further, it is recommended to evaluate the feasibility of this plant to be used in the field as a control intervention in integrated vector management programmes.

Integrated vector management program in the framework of the COVID-19 pandemic in Medellin, Colombia

Introduction: The COVID-19 pandemic pressured health care systems to remain alert and active in their vector-borne disease control and prevention programs, leading to changes in vector control strategies in urban areas affected by dengue, Zika and chikungunya. Objective: To describe the adaptations made to the vector control and surveillance program in Medellín during the COVID-19 health emergency. Materials and methods: Once the health emergency started, biosecurity protocols were developed. Entomological surveillance was strengthened from the institutional environment instead of homes. Data was collected in Medellín from 2018 to 2021 during the vector control and surveillance program activities, which included epidemiological and entomovirological surveillance, entomological index survey, ovitrap monitoring, community mobilization, search and elimination of mosquito breading sites, and chemical control. These actions were adapted and/or increased to promote self-care among communities in total and partial confinement, and to develop prevention and control measures. Results: Mosquito monitoring was increased by 40% using ovitraps, entomological virological surveillance showed an increase in 2020 of 34,4% compared to 2019 and virtual media was used to keep and improve contact with the community. Conclusion: The COVID-19 pandemic had a significant impact on arbovirus prevention and control programs. The city of Medellín quickly adapted its entomo-virological surveillance activities, control measures, and the contact with the community during the pandemic, which allow the Integrated Vector Management program to remain active in the city.

Distance from human dwellings differentially affects the efficacy of a synthetic cattle urine odour lure to trap malaria vectors

BackgroundCost–effective outdoor–based devices for surveillance and control of outdoor mosquito vector populations can substantially improve their efficacy when baited with synthetic human and animal odours. This study aimed at assessing the dose–dependent efficacy of a previously developed synthetic cattle urine odour to lure malaria vectors, and other mosquito species, to traps placed at different distances from human dwellings outdoors.MethodsThe efficacy of the cattle urine odour lure was assessed through a 5 × 5 Latin square design, using two sets of 5 Suna traps placed at either 1.5 m or 5 m from an adjacent human dwelling, in the rural village of Sagamaganga, Tanzania. Each trap was deployed with one of four doses of the synthetic cattle urine odour blend or a solvent control (heptane). Traps were rotated daily so that each dose and control visited each position twice over a period of 20 experimental nights. The relative attractiveness of each treatment dose and control was compared using a generalized linear mixed model for each species caught.ResultsA total of 1568 mosquitoes were caught, of which 783 were anophelines and 785 were culicines. Of the anophelines, 41.6 and 58.3% were primary and secondary vector species, respectively. Unfed and fed females of the primary vector, Anopheles arabiensis, were caught dose–dependently, close to human dwellings (1.5 m), whereas unfed, fed and gravid secondary vector Anopheles pharoensis females were caught dose–dependently, but at a farther distance from the dwellings (5 m). Females of Culex spp. were caught dose–dependently in similar numbers irrespective of the distance from human dwellings.ConclusionsThis study further clarifies the factors to be considered for the implementation of outdoor trapping using the synthetic cattle urine lure to target exophilic and exophagic malaria vectors, for which efficient surveillance and control tools are currently lacking. The findings resulting from this study make significant progress in providing the needed information to overcome the regulatory obstacles to make this tool available for integrated vector management programs, including registration, as well as evaluation and regulation by the World Health Organization.

First comprehensive report of the resistance of Culex quinquefasciatus Say (Diptera: Culicidae) to commonly used insecticides in Riyadh, Saudi Arabia

The mosquito Culex quinquefasciatus is a vector of various pathogens including West Nile virus, Saint Louis encephalitis virus, and Western equine encephalitis virus. Insecticides are the main tools for Cx. quinquefasciatus control, but this overreliance on chemical tools has led to the development of resistance to many insecticides in this important insect vector. The resistance of eight field populations of Cx. quinquefasciatus to 10 commonly used insecticides was evaluated. Based on the resistance ratios (RRs), the adults of Cx. quinquefasciatus field populations displayed susceptibility to the organophosphates (OPs) except Al-Masanie adults which exhibited low resistance to fenitrothion (RR50 = 3.62). Conversely, the mosquitoes exhibited susceptibility, low resistance, and moderate resistance to the pyrethroids alpha-cypermethrin (RR = 0.59–2.56), bifenthrin (RR = 0.59–2.19), deltamethrin (RR = 0.60–7.07), cypermethrin (RR = 0.60–2.66), and cyfluthrin (RR = 0.58–2.39). At the larval stage, Cx. quinquefasciatus field populations displayed susceptibility to low resistance to the OPs chlorpyrifos (RR = 0.03–1.75), malathion (RR = 0.19–3.42), fenitrothion (RR = 0.11–2.78), and pirimiphos-methyl (RR = 0.08–1.15). Although these results in Cx. quinquefasciatus field populations indicated that the OPs and pyrethroids maintained high efficacy in controlling this species in the geographical area of this study, these findings should be utilized wisely to avoid any potential negative effects on human health and environmental safety attributable to the application of these broad-spectrum conventional insecticides. However, these findings provide a solid basis for decision-making for Cx. quinquefasciatus integrated vector management programs.

Characterization of triatomine bloodmeal sources using direct Sanger sequencing and amplicon deep sequencing methods

Knowledge of host associations of blood-feeding vectors may afford insights into managing disease systems and protecting public health. However, the ability of methods to distinguish bloodmeal sources varies widely. We used two methods—Sanger sequencing and amplicon deep sequencing—to target a 228 bp region of the vertebrate Cytochrome b gene and determine hosts fed upon by triatomines (n = 115) collected primarily in Texas, USA. Direct Sanger sequencing of PCR amplicons was successful for 36 samples (31%). Sanger sequencing revealed 15 distinct host species, which included humans, domestic animals (Canis lupus familiaris, Ovis aries, Gallus gallus, Bos taurus, Felis catus, and Capra hircus), wildlife (Rattus rattus, Incilius nebulifer, Sciurus carolinensis, Sciurus niger, and Odocoileus virginianus), and captive animals (Panthera tigris, Colobus spp., and Chelonoidis carbonaria). Samples sequenced by the Sanger method were also subjected to Illumina MiSeq amplicon deep sequencing. The amplicon deep sequencing results (average of 302,080 usable reads per sample) replicated the host community revealed using Sanger sequencing, and detected additional hosts in five triatomines (13.9%), including two additional blood sources (Procyon lotor and Bassariscus astutus). Up to four bloodmeal sources were detected in a single triatomine (I. nebulifer, Homo sapiens, C. lupus familiaris, and S. carolinensis). Enhanced understanding of vector-host-parasite networks may allow for integrated vector management programs focusing on highly-utilized and highly-infected host species.

Defining the mechanisms of action and mosquito larva midgut response to a yeast-encapsulated orange oil larvicide

BackgroundYeast-encapsulated orange oil (YEOO) is a novel, ingestible larvicide that combines the benefits of a low-cost essential oil with yeast, an attractive food source for mosquito larvae. In this work, we investigated the underlying mechanisms of action associated with YEOO ingestion by Aedes aegypti larvae.MethodsAedes aegypti third-stage larvae (L3) were treated with sublethal or lethal concentrations of YEOO. Genes associated with apoptosis, autophagy and innate immune responses were investigated by RT-qPCR in guts and carcasses dissected from treated and control larvae. Differential expression of cytochrome P450 genes in the CYP6 and CYP9 families were also investigated. Confocal and transmission electron microscopy were used to assess damage caused by YEOO throughout the larval alimentary canal. TUNEL was used to assess apoptosis via DNA fragmentation.ResultsThe apoptosis genes IAP1 and IAP2 in larvae displayed opposing effects following exposure to lethal doses of YEOO, with a 26-fold induction of IAP1 at 8 h post YEOO ingestion. The effector caspase CASPS8 displayed a 6.7-fold induction in the gut and concomitant 70-fold induction in the carcass at 8 h post YEOO ingestion. The midgut epithelia regenerator, Vein, had an 11-fold induction in the gut after 4 h and was repressed 7.6-fold in the carcass at 24 h. Sublethal concentrations (< LC50) led to significant differential expression of CYP6 and CYP9 genes. Midgut epithelial damage was highlighted by the destruction of microvilli, vacuolization of midgut cells and damage to cell junctions and basal lamina as early as 30 min. Larval type 2 peritrophic matrix structural integrity and porosity remain unchanged.ConclusionOur results strongly suggest that the robust larvicidal activity of YEOO is due to a generalized broad-acting mechanism combining epithelial damage and apoptosis, with concomitant expression of multiple innate response genes involved in epithelial regeneration and detoxification. YEOO’s amenability for use as part of an integrated vector management program makes this novel larvicide a practical approach for mosquito larval control in the future.Graphical

Fitness Cost of Sequential Selection with Deltamethrin in Aedes aegypti (Diptera: Culicidae).

In Mexico, Aedes aegypti (L.) is the primary dengue vector, chikungunya, and Zika viruses. The continued use of synthetic pyrethroids has led to the development of resistance in target populations, which has diminished the effectiveness of vector control programs. Resistance has been associated with disadvantages that affect the biological parameters of resistant mosquitoes compared to susceptible ones. In the present study, the disadvantages were evaluated by parameters related to survival and reproduction ('fitness cost') after selection with deltamethrin for five generations. The parameters analyzed were the length of the development cycle, sex ratio, survival, longevity, fecundity, egg viability, preoviposition, oviposition and postoviposition periods, and growth parameters. In the deltamethrin-selected strain, there was a decrease in the development cycle duration, the percentage of pupae, the oviposition period, and eggs viability. Although mean daily fecundity was not affected after the selection process, this, together with the decrease in the survival and fecundity levels by specific age, significantly affected the gross reproductive rate (GRR), net reproductive rate (Ro), and intrinsic growth rate (rm) of the group selected for five generations with deltamethrin compared to the group without selection. Identifying the 'cost' of resistance in biological fitness represents an advantage if it is desired to limit the spread of resistant populations since the fitness cost is the less likely that resistant individuals will spread in the population. This represents an important factor to consider in designing integrated vector management programs.

Field evaluation of WALS truck-mounted A1 super duty mist sprayer\xae with VectoBac\xae WDG against Aedes aegypti (Diptera:Culicidae) populations in Manatee County, Florida

Aedes aegypti, the Dengue and Zika vector, is a domestic mosquito that is difficult to control. The challenge lies in the mosquito’s preference to lay its eggs in cryptic habitats such as fence post openings, buckets and bird baths, cups. Additionally, current methods of control are labor-intensive. We employed the WALS strategy to evaluate the operational efficacy of applying VectoBac WDG using a truck-mounted mister to control local populations of Ae. aegypti in urban settings with difficult-to-reach larval mosquito habitats. Our study was conducted in Cortez (Manatee County), Florida, USA (27° 27’ N, 82° 40’ W). We selected two study sites, one untreated control (21.9 ha) and one treatment site (23.1 ha) where historical data have shown high populations of Ae. aegypti based on weekly ovitrap surveillance. Weekly BGs and ovitraps (10–15 traps/site) were deployed to monitor adult population dynamics. A total of 50 bioassay jars were placed in the field each afternoon of the Bti application (8 application events) at fixed locations to collect droplets and gauge efficacy. We found significant reduction in female adults (P = 0.0002) and landing rate counts (P = 0.0058) as a result of treatment. Larval bioassays during the eight applications confirmed Bti deposit in a variety of coverage types regardless of placement in the yards. WALS applications with a truck-mounted mister can be effective at reducing disease carrying mosquito populations in residential areas and can be implemented in an integrated vector management program.

First Evaluation of Field Evolved Resistance to Commonly Used Insecticides in House Fly Populations from Saudi Arabian Dairy Farms

Simple SummaryThe house fly is one of the major carriers of several diseases that affect humans and animals. Insecticides are often used as a rapid method to control them. In this study, eight commonly used insecticides were tested against five populations of house flies collected from dairies around Riyadh, Saudi Arabia. The aim was to evaluate how toxic the insecticides were, and to find out whether the flies showed any sign of resistance against insecticides. In the tested pyrethroid insecticides, there was no or only moderate resistance in adults of both sexes compared to a known susceptible strain. In the tested organophosphate insecticides, there was low to moderate resistance in adults of both sexes compared to the susceptible strain. This study also evaluated “median lethal times” for the tested insecticides (how long a certain dose takes to kill half the exposed population), with results available for all eight insecticides: alpha-cypermethrin, deltamethrin, bifenthrin, cypermethrin, cyfluthrin, fenitrothion, chlorpyrifos, and malathion. The results of this study will be helpful for people whose job it is to plan effective house fly control programs in Saudi Arabia.The house fly, Musca domestica L. (Diptera: Muscidae), is one of the major vectors of several pathogens that affect humans and animals. We evaluated the toxicity of eight insecticides commonly used for house fly control using five field populations collected from dairies in Riyadh, Saudi Arabia. Among the five tested pyrethroids, non to moderate resistance was found in adults of both sexes compared to a susceptible strain. Resistance ratios ranged from 0.5- to 7-fold for alpha-cypermethrin, 2- to 21-fold for deltamethrin, 4- to 19-fold for bifenthrin, 1- to 9-fold for cyfluthrin, and 1- to 8-fold for cypermethrin. Among the three tested organophosphates, low to moderate resistance was found among adult flies compared to the susceptible strain, and the resistance ratios ranged from 4- to 27-fold for fenitrothion, 2- to 14-fold for chlorpyrifos, and 3- to 12-fold for malathion. The median lethal times for the tested insecticides were 3–33 h for alpha-cypermethrin, 3–24 h for deltamethrin, 5–59 h for bifenthrin, 1–7 h for cypermethrin, 0.3–7 h for cyfluthrin, 6–36 h for fenitrothion, 2–21 h for chlorpyrifos, and 3–34 h for malathion. This study presents baseline data pertaining to registered public health insecticides, and the results will assist future studies monitoring insecticide resistance, and the planning of effective integrated vector management programs.

Extracts of Amazonian Fungi With Larvicidal Activities Against Aedes aegypti.

The global increase in diseases transmitted by the vector Aedes aegypti, new and re-emerging, underscores the need for alternative and more effective methods of controlling mosquitoes. Our aim was to identify fungal strains from the Amazon rain forest that produce metabolites with larvicidal activity against Aedes aegypti. Thirty-six fungal strains belonging to 23 different genera of fungi, isolated from water samples collected in the state of Amazonas, Brazil were cultivated. The liquid medium was separated from the mycelium by filtration. Medium fractions were extracted with ethyl acetate and isopropanol 9:1 volume:volume, and the mycelia with ethyl acetate and methanol 1:1. The extracts were vacuum dried and the larvicidal activity was evaluated in selective bioassays containing 500 μg/ml of the dried fungal extracts. Larval mortality was evaluated up to 72 h. None of the mycelium extracts showed larvicidal activity greater than 50% at 72 h. In contrast, 15 culture medium extracts had larvicidal activity equal to or greater than 50% and eight killed more than 90% of the larvae within 72 h. These eight extracts from fungi belonging to seven different genera (Aspergillus, Cladosporium, Trichoderma, Diaporthe, Albifimbria, Emmia, and Sarocladium) were selected for the determination of LC50 and LC90. Albifimbria lateralis (1160) medium extracts presented the lowest LC50 value (0.268 μg/ml) after 24 h exposure. Diaporthe ueckerae (1203) medium extracts presented the lowest value of LC90 (2.928 μg/ml) at 24 h, the lowest values of LC50 (0.108 μg/ml) and LC90 (0.894 μg/ml) at 48 h and also at 72 h (LC50 = 0.062 μg/ml and LC90 = 0.476 μg/ml). Extracts from Al. lateralis (1160) and D. ueckerae (1203) showed potential for developing new, naturally derived products, to be applied in integrated vector management programs against Ae. aegypti.

Paved Paradise: Belowground Parking Structures Sustain Urban Mosquito Populations in Washington, DC.

After notification of mosquitoes within federal buildings in Washington, DC, we surveyed belowground levels of nearby parking structures for mosquitoes and standing water in the summer months of 2018 and 2019. Aedes aegypti, Ae. albopictus, and members of the Culex pipiens Assemblage were found. Genotyping revealed pipiens, molestus, and quinquefasciatus ancestry among Cx. pipiens Assemblage mosquitoes, and allele frequency comparisons indicated a stable, resident population. Winter and spring aboveground temperatures ranged from -11°C to 35°C, while belowground temperatures never dropped below 5°C or exceeded 30°C, and winter temperatures were significantly higher belowground compared with aboveground. Moderated winter conditions suggest that belowground urban structures could act as refugia for warmer-climate species, like Ae. aegypti and Cx. quinquefasciatus, allowing them to overcome assumed thermal barriers. Surveys of parking structures should be incorporated into integrated vector management programs in urban areas.

A Field Efficacy Evaluation of In2Care Mosquito Traps in Comparison with Routine Integrated Vector Management at Reducing Aedes aegypti.

Aedes aegypti is the predominant vector of dengue, chikungunya, and Zika viruses. This mosquito is difficult to control with conventional methods due to its container-inhabiting behavior and resistance to insecticides. Autodissemination of pyriproxyfen (PPF), a potent larvicide, has shown promise as an additional tool to control Aedes species in small-scale field trials. However, few large-scale field evaluations have been conducted. We undertook a 6-month-long large-scale field study to compare the effectiveness and operational feasibility of using In2Care Mosquito Traps (In2Care Traps, commercially available Aedes traps with PPF and Beauveria bassiana) compared to an integrated vector management (IVM) strategy consisting of source reduction, larviciding, and adulticiding for controlling Ae. aegypti eggs, larvae, and adults. We found that while the difference between treatments was only statistically significant for eggs and larvae (P < 0.05 for eggs and larvae and P > 0.05 for adults), the use of In2Care Traps alone resulted in 60%, 57%, and 57% fewer eggs, larvae, and adults, respectively, collected from that site compared to the IVM site. However, In2Care Trap deployment and maintenance were more time consuming and labor intensive than the IVM strategy. Thus, using In2Care Traps alone as a control method for large areas (e.g., >20 ha) may be less practical for control programs with the capacity to conduct ground and aerial larviciding and adulticiding. Based on our study results, we conclude that In2Care Traps are effective at suppressing Ae. aegypti and have the most potential for use in areas without sophisticated control programs and within IVM programs to target hotspots with high population levels and/or risk of Aedes-borne pathogen transmission.

Insecticide resistance to insect growth regulators, avermectins, spinosyns and diamides in Culex quinquefasciatus in Saudi Arabia

BackgroundCulex quinquefasciatus is not only a biting nuisance but also an important vector of fatal diseases. In Saudi Arabia, management measures to control this mosquito and thereby prevent associated disease transmission have focused on insecticides. Nevertheless, information on the resistance status of C. quinquefasciatus is insufficient, especially concerning insecticides containing novel classes of insecticides.MethodsWe evaluated six insecticides belonging to four classes of insecticides (insect growth regulators [3], avermectins [1], diamides [1] and spinosyns [1]) for toxicity and resistance in eight C. quinquefasciatus populations (from Ishbiliya, Al-Masfa, Al-Masanie, Al-Washlah, Al-Nakhil, Irqah, Al-Suwaidi and Al-Ghanemiya) following World Health Organisation protocols.ResultsResistance status ranging from susceptibility/low resistance to high resistance, in comparison with the susceptible strain, was detected for cyromazine in the eight C. quinquefasciatus populations: Ishbiliya (resistance ratio [RR] = 3.33), Al-Masfa (RR = 4.33), Al-Masanie (RR = 3.67), Al-Washlah (RR = 2.33), Al-Nakhil (RR = 5.33), Irqah (RR = 7.00), Al-Suwaidi (RR = 21.33) and Al-Ghanemiya (RR = 16.00). All C. quinquefasciatus populations exhibited a high level of resistance to diflubenzuron (RR = 13.33–43.33), with the exception of Al-Nakhil which exhibited moderate resistance (RR = 10.00). Susceptibility/low resistance to high resistance was observed for triflumuron in the eight C. quinquefasciatus populations: Ishbiliya (RR = 0.50), Al-Ghanemiya (RR = 3.00), Al-Suwaidi (RR = 10.00), Al-Masfa (RR = 5.00), Al-Masanie (RR = 10.00), Al-Nakhil (RR = 5.00), Irqah (RR = 5.00) and Al-Washlah (RR = 15.00). Susceptibility/low resistance was assessed for abamectin, chlorantraniliprole and spinosad in all C. quinquefasciatus populations, with RR ranges of 0.25–3.50, 0.17–2.19, and 0.02–0.50, respectively. However, the population collected from Irqah showed high resistance to chlorantraniliprole (RR = 11.93).ConclusionsThe detection of widespread resistance to insect growth regulators in C. quinquefasciatus highlights an urgent need to establish integrated vector management strategies. Our results may facilitate the selection of potent insecticides for integrated vector management programmes for C. quinquefasciatus.Graphical

Evaluating and strengthening the health system of Cura\u04abao to improve its performance for future outbreaks of vector-borne diseases

BackgroundVector-borne diseases (VBDs) such as dengue, chikungunya, and Zika pose a significant challenge to health systems in countries they affect, especially countries with less developed healthcare systems. Therefore, countries are encouraged to work towards more resilient health systems. This qualitative study aims to examine the performance of the health system of the Dutch Caribbean island of Curaҫao regarding the prevention and control of VBDs in the last decade by using the WHO health system building blocks.MethodsFrom November 2018 to December 2020, a multi-method qualitative study was performed in Curaçao, applying content analysis of documents (n = 50), five focus group discussions (n = 30), interviews with experts (n = 11) and 15 observation sessions. The study was designed based on the WHO framework: health system building blocks. Two cycles of inductive and deductive coding were employed, and Nvivo software was used to analyse the data.ResultsThis study’s data highlighted the challenges (e.g. insufficient oversight, coordination, leadership skills, structure and communication) that the departments of the health system of Curaҫao faced during the last three epidemics of VBDs (2010–2020). Furthermore, low levels of collaboration between governmental and non-governmental organisations (e.g. semi-governmental and private laboratories) and insufficient capacity building to improve skills (e.g. entomological, surveillance skills) were also observed. Lastly, we observed how bottlenecks in one building block negatively influenced other building blocks (e.g. inadequate leadership/governance obstructed the workforce's performance).ConclusionsThis study uncovers potential organisational bottlenecks that have affected the performance of the health system of Curaҫao negatively. We recommend starting with the reinforcement of oversight of the integrated vector management programme to ensure the development, implementation and evaluation of related legislation, policies and interventions. Also, we recommend evaluating and reforming the existing administrative and organisational structure of the health system by considering the cultural style, challenges and barriers of the current health system. More efforts are needed to improve the documentation of agreements, recruitment and evaluation of the workforce's performance. Based on our findings, we conceptualised actions to strengthen the health system's building blocks to improve its performance for future outbreaks of infectious diseases.Graphical abstract

Effectiveness of integrated Aedes albopictus management in southern Switzerland

BackgroundThe exotic invasive tiger mosquito, Aedes albopictus, appeared in southern Switzerland in 2003. The spread of the mosquito has been surveyed constantly since then, and an integrated vector management (IVM) has been implemented to control its numbers. The control measures focus on the aquatic phase of the mosquito with removal of breeding sites and applications of larvicides in public areas whereas private areas are reached through extensive public information campaigns. Here, we evaluated the efficacy of the IVM.MethodsSince all the municipalities with Ae. albopictus in southern Switzerland are currently implementing the IVM, Italian municipalities just across the Swiss-Italian border, where Ae. albopictus is present but no coordinated intervention programme is in place, served as control. Ovitraps and adult female traps were used to measure mosquito abundance in 2019. Generalised mixed-effects models were used to model the numbers of Ae. albopictus eggs and adult females collected. These numbers of Ae. albopictus eggs were compared to the numbers of eggs collected in 2012 and 2013 in a previous assessment of the IVM, using a hurdle model.ResultsMean numbers of Ae. albopictus eggs and adult females in 2019 were consistently higher in the municipalities not following an IVM programme. In these municipalities, there were about four times (3.8) more eggs than in the municipalities implementing an IVM programme. Also, the numbers of eggs and adult females increased steadily from the beginning of the Ae. albopictus reproductive season, reaching a peak in August. In contrast, the increase in numbers of Ae. albopictus was much more contained in the municipalities implementing an IVM programme, without reaching an evident peak. Comparison with data from 2012 and 2013 indicates that the gap between intervention and non-intervention areas may have almost doubled in the past 6 years.ConclusionsThe results of the survey strongly support the efficacy of the IVM programme implemented in southern Switzerland compared to municipalities without defined control measures. With the constant implementation of an IVM, it appears possible to contain the numbers of Ae. albopictus at a manageable level, reducing the nuisance for the human population and the risk of arbovirus epidemics.Graphical

A Three-Pronged Approach to Studying Sublethal Insecticide Doses: Characterising Mosquito Fitness, Mosquito Biting Behaviour, and Human/Environmental Health Risks.

Simple SummaryExtensive research has been carried out to assess the effects of sublethal pyrethroid doses on mosquito fitness and behaviour. Although pyrethroids are mainly used as insecticides, they can also act as repellents, depending on the dosage and/or exposure time. Females and males of two laboratory-reared mosquito species (Culex pipiens and Aedes albopictus) were exposed to five treatments in the laboratory: three doses of the pyrethroid prallethrin, as well as an untreated and a negative control. Effects on mosquito fitness, mosquito biting behaviour, and human and environmental health were evaluated. Sublethal prallethrin doses were found to decrease mosquito population size, longevity, and biting rate while posing low risks to human and environmental health. Such changes in adult mosquito fitness and behaviour could reduce the ability of mosquitoes to transmit diseases and, consequently, help limit public health risks. Although these promising results suggest sublethal insecticide doses could offer a new approach to controlling species that transmit diseases, more work is needed to identify the proper balance among regulatory requirements, contexts of usage, and human and environmental health benefits.Worldwide, pyrethroids are one of the most widely used insecticide classes. In addition to serving as personal protection products, they are also a key line of defence in integrated vector management programmes. Many studies have assessed the effects of sublethal pyrethroid doses on mosquito fitness and behaviour. However, much remains unknown about the biological, physiological, demographic, and behavioural effects on individual mosquitoes or mosquito populations when exposure occurs via spatial treatments. Here, females and males of two laboratory-reared mosquito species, Culex pipiens and Aedes albopictus, were exposed to five different treatments: three doses of the pyrethroid prallethrin, as well as an untreated and a negative control. The effects of each treatment on mosquito species, sex, adult mortality, fertility, F1 population size, and biting behaviour were also evaluated. To compare knockdown and mortality among treatments, Mantel–Cox log-rank tests were used. The results showed that sublethal doses reduced mosquito survival, influencing population size in the next generation. They also provided 100% protection to human hosts and presented relatively low risks to human and environmental health. These findings emphasise the need for additional studies that assess the benefits of using sublethal doses as part of mosquito management strategies.

High larvicidal efficacy of yeast-encapsulated orange oil against Aedes aegypti strains from Brazil

BackgroundBotanical substances such as essential oils (EOs) have demonstrated insecticidal properties and are a valid option for vector control. However, free EOs are unreliable as mosquito larvicides due their easy degradation by environmental exposure to ultraviolet light and higher temperatures. Here, we assessed the efficacy of a mosquito larvicide based on orange oil in a yeast-based delivery system against Aedes aegypti strains with different resistance status towards chemical neurotoxic insecticides. This larvicide preparation was physicochemically characterized in a previous report.MethodsLarvae of four Ae. aegypti strains from different regions of Brazil and different resistance profiles for deltamethrin (pyrethroid) and temephos (organophosphate) were tested against yeast-encapsulated orange oil (YEOO) in laboratory conditions for measurement of LC50 and LC90 values. The same assays were performed with the Belo Horizonte strain under environmental conditions (natural light and temperature). The resistance profiles of these strains were compared to the Rockefeller reference strain in all conditions.ResultsYEOO was found to be a highly active larvicide (LC50 < 50 mg/L) against all Ae. aegypti strains tested in both laboratory conditions (LC50 = 8.1–24.7 mg/L) and environmental conditions with natural light and temperature fluctuation (LC50 = 20.0–49.9 mg/L). Moreover, all strains were considered susceptible (RR < 5) to YEOO, considering resistance ratios calculated based on the Rockefeller strain. The resistance ratios were only higher than 2.5 for LC90–95 of Belo Horizonte in the laboratory, probably due the higher heterogeneity associated with older egg papers (> 5 months).ConclusionYEOO demonstrates high larvicidal activity against Ae. aegypti strains with resistant phenotypes for deltamethrin (PY) and temephos (OP). This larvicidal activity suggests the potential for the development of YEOO as an alternative intervention to synthetic insecticides in integrated vector management programs, for populations with resistance to commonly used insecticides.Graphical