Efficacy of a spatial repellent for control of Aedes-borne virus transmission: A cluster-randomized trial in Iquitos, Peru.

Over half the world's population is at risk for viruses transmitted by Aedes mosquitoes, such as dengue and Zika. The primary vector, Aedes aegypti, thrives in urban environments. Despite decades of effort, cases and geographic range of Aedes-borne viruses (ABVs) continue to expand. Rigorously proven vector control interventions that measure protective efficacy against ABV diseases are limited to Wolbachia in a single trial in Indonesia and do not include any chemical intervention. Spatial repellents, a new option for efficient deployment, are designed to decrease human exposure to ABVs by releasing active ingredients into the air that disrupt mosquito-human contact. A parallel, cluster-randomized controlled trial was conducted in Iquitos, Peru, to quantify the impact of a transfluthrin-based spatial repellent on human ABV infection. From 2,907 households across 26 clusters (13 per arm), 1,578 participants were assessed for seroconversion (primary endpoint) by survival analysis. Incidence of acute disease was calculated among 16,683 participants (secondary endpoint). Adult mosquito collections were conducted to compare Ae. aegypti abundance, blood-fed rate, and parity status through mixed-effect difference-in-difference analyses. The spatial repellent significantly reduced ABV infection by 34.1% (one-sided 95% CI lower limit, 6.9%; one-sided P value = 0.0236, z = 1.98). Aedes aegypti abundance and blood-fed rates were significantly reduced by 28.6 (95% CI 24.1%, ∞); z = -9.11) and 12.4% (95% CI 4.2%, ∞); z = -2.43), respectively. Our trial provides conclusive statistical evidence from an appropriately powered, preplanned cluster-randomized controlled clinical trial of the impact of a chemical intervention, in this case a spatial repellent, to reduce the risk of ABV transmission compared to a placebo.

Impact of a spatial repellent intervention on Anopheles kdr insecticide resistance allele in Sumba, Indonesia.

BACKGROUND: The emergence of insecticide resistance and outdoor transmission in malaria-endemic areas underlines the urgent need to develop innovative tools, such as spatial repellents (SR), that may circumvent this residual transmission. With limited options for effective insecticides, regular resistance monitoring is warranted for selecting and using appropriate tools. This study evaluates the pyrethroid knockdown resistance (kdr) allele before and after implementing a transfluthrin-based spatial repellent (SR) intervention in placebo-treated clusters. METHODS: This study looks at the frequency distribution of the kdr allele in Sumba Island from June 2015 to August 2018. Insecticide susceptibility tests were carried out on female Anopheles sp. aged 3-5 days against permethrin 21.5 µg/ml, deltamethrin 12.5 µg/ml, and transfluthrin 10 µg/ml using CDC bottle assay. PCR sequencing of representative samples from adult mosquito collections and insecticide tests revealed the presence of kdr mutations (L1014F and L1014S) in the VGSC gene. RESULTS: A total of 12 Anopheles species, Anopheles tesselatus, Anopheles. aconitus, Anopheles barbirostris, Anopheles kochi, Anopheles annularis, Anopheles maculatus, Anopheles sundaicus, Anopheles flavirostris, Anopheles balabacensis, Anopheles indefinitus, Anopheles subpictus, and Anopheles vagus were analysed. Anopheles vagus and An. sundaicus predominated in the larval populations. Susceptibility assays for all insecticides identified fully susceptible phenotypes in all species examined. Anopheles increasing frequency of kdr mutant alleles during the 3 year SR deployment was observed in both SR-treated and placebo areas, a statistically significant increase occurred in each arm. However, it is unclear how significant SR is in causing the increase in mutant alleles. The L1014S, knockdown resistance east type (kdr-e) allele was detected for the first time among the mosquito samples in this study. The L1014F, knockdown resistance west type (kdr-w) allele and heteroduplex form (wild-type-mutant) were found in almost all Anopheles species examined, including An. vagus, An. aconitus, An. subpictus, An. tesselatus, An. annularis, An. flavirostris and An. sundaicus. CONCLUSION: The presence of fully susceptible phenotypes over time, along with an increase in the frequency distribution of the L1014F/S mutations post-intervention, suggest drivers of resistance external to the study, including pyrethroid use in agriculture and long-lasting insecticidal nets (LLINs). However, this does not negate possible SR impacts that support resistance. More studies that enable the comprehension of possible SR-based drivers of resistance in mosquitoes need to be conducted.

Early morning anopheline mosquito biting, a potential driver of malaria transmission in Busia County, western Kenya.

BACKGROUND: Insecticide-treated nets (ITNs) contributed significantly to the decline in malaria since 2000. Their protective efficacy depends not only on access, use, and net integrity, but also location of people within the home environment and mosquito biting profiles. Anopheline mosquito biting and human location data were integrated to identify potential gaps in protection and better understand malaria transmission dynamics in Busia County, western Kenya. METHODS: Direct observation of human activities and human landing catches (HLC) were performed hourly between 1700 to 0700 h. Household members were recorded as home or away; and, if at home, as indoors/outdoors, awake/asleep, and under a net or not. Aggregated data was analysed by weighting hourly anopheline biting activity with human location. Standard indicators of human-vector interaction were calculated using a Microsoft Excel template. RESULTS: There was no significant difference between indoor and outdoor biting for Anopheles gambiae sensu lato (s.l.) (RR = 0.82; 95% CI 0.65-1.03); significantly fewer Anopheles funestus were captured outdoors than indoors (RR = 0.41; 95% CI 0.25-0.66). Biting peaked before dawn and extended into early morning hours when people began to awake and perform routine activities, between 0400-0700 h for An. gambiae and 0300-0700 h for An. funestus. The study population away from home peaked at 1700-1800 h (58%), gradually decreased and remained constant at 10% throughout the night, before rising again to 40% by 0600-0700 h. When accounting for resident location, nearly all bites within the peri-domestic space (defined as inside household structures and surrounding outdoor spaces) occurred indoors for unprotected people (98%). Using an ITN while sleeping was estimated to prevent 79% and 82% of bites for An. gambiae and An. funestus, respectively. For an ITN user, most remaining exposure to bites occurred indoors in the hours before bed and early morning. CONCLUSION: While use of an ITN was estimated to prevent most vector bites in this context, results suggest gaps in protection, particularly in the early hours of the morning when biting peaks and many people are awake and active. Assessment of additional human exposure points, including outside of the peri-domestic setting, are needed to guide supplementary interventions for transmission reduction.

Oral susceptibility to ivermectin is over fifty times greater in a wild population of Anopheles albimanus mosquitoes from Belize than the STECLA laboratory reference strain of this mosquito.

BACKGROUND: The STECLA strain of Anopheles albimanus has been in continuous colony for many years and is the reference strain on which genomic studies for the species are based. Recently, the STECLA strain was demonstrated to be much less susceptible to ivermectin ingested in a blood meal (4-day LC50 of 1468 ng/ml) than all other Anopheles species tested to-date (LC50 values range from 7 to 56 ng/ml). The ability of An. albimanus to survive ingestion of ivermectin at concentrations far beyond that typically found in the blood of ivermectin-treated people or livestock (i.e., 30-70 ng/ml) could invalidate the use of ivermectin as a malaria vector control strategy in areas where An. albimanus is a primary vector. METHODS: To investigate this, host-seeking An. albimanus were captured in northern Belize and used in membrane feeding bioassays of ivermectin, employing the same methods as described earlier with the STECLA strain. RESULTS: Field-collected An. albimanus in Belize were 55 times more susceptible to ingested ivermectin than were the STECLA reference strain. Oral susceptibility to ivermectin in wild An. albimanus from Belize (4-day LC50 of 26 ng/ml) was equivalent to that of other Anopheles species tested. CONCLUSIONS: Contrary to initial assessments using a highly inbred strain of mosquito, laboratory studies using a field population indicate that ivermectin treatment of livestock could reduce An. albimanus populations in areas of Central America and the Caribbean where malaria transmission may occur. Toxicity screening of ivermectin and other systemic parasiticides for malaria control should examine wild populations of the vector species being targeted.

Scientific achievements and reflections after 20 years of vector biology and control research at the Pu Teuy mosquito field research station, Thailand.

Additional vector control tools are needed to supplement current strategies to achieve malaria elimination and control of Aedes-borne diseases in many settings in Thailand and the Greater Mekong Sub-region. Within the next decade, the vector control community, Kasetsart University (KU), and the Ministry of Higher Education, Science, Research and Innovation must take full advantage of these tools that combine different active ingredients with different modes of action. Pu Teuy Mosquito Field Research Station (MFRS), Department of Entomology, Faculty of Agriculture, Kasetsart University (KU), Thailand was established in 2001 and has grown into a leading facility for performing high-quality vector biology and control studies and evaluation of public health insecticides that are operationally relevant. Several onsite mosquito research platforms have been established including experimental huts, a 40-m long semi-field screening enclosure, mosquito insectary, field-laboratory, and living quarters for students and researchers. Field research and assessments ranged from 'basic' investigations on mosquito biology, taxonomy and genetics to more 'applied' studies on responses of mosquitoes to insecticides including repellency, behavioural avoidance and toxicity. In the course of two decades, 51 peer-reviewed articles have been published, and 7 masters and 16 doctoral degrees in Entomology have been awarded to national and international students. Continued support of key national stakeholders will sustain MFRS as a Greater Mekong Subregion centre of excellence and a resource for both insecticide trials and entomological research.

Impact of a spatial repellent product on Anopheles and non-Anopheles mosquitoes in Sumba, Indonesia.

BACKGROUND: The East Nusa Tenggara province, Indonesia, contributed to 5% of malaria cases nationally in 2020, with other mosquito-borne diseases, such as dengue and filariasis also being endemic. Monitoring of spatial and temporal vector species compositions and bionomic traits is an efficient method for generating evidence towards intervention strategy optimization and meeting disease elimination goals. METHODS: The impact of a spatial repellent (SR) on human biting mosquitoes was evaluated as part of a parent cluster-randomized, double-blinded, placebo-controlled trial, in Sumba, East Nusa Tenggara. A 10-month (June 2015-March 2016) baseline study was followed by a 24-month intervention period (April 2016 to April 2018)-where half the clusters were randomly assigned either a passive transfluthrin emanator or a placebo control. RESULTS: Human-landing mosquito catches documented a reduction in landing rates related to the SR. Overall, there was a 16.4% reduction (21% indoors, and 11.3% outdoors) in human biting rates (HBR) for Anopheles. For Aedes, there was a 44.3% HBR reduction indoors and a 35.6% reduction outdoors. This reduction was 38.3% indoors and 39.1% outdoors for Armigeres, and 36.0% indoors and 32.3% outdoors for Culex species. Intervention impacts on the HBRs were not significant and are attributed to large inter-household and inter cluster variation. Anopheles flavirostris, Anopheles balabacensis and Anopheles maculatus individually impacted the overall malaria infections hazard rate with statistically significance. Though there was SR-based protection against malaria for all Anopheles species (except Anopheles sundaicus), only five (Anopheles aconitus, Anopheles kochi, Anopheles tessellatus, An. maculatus and An. sundaicus) demonstrated statistical significance. The SR numerically reduced Anopheles parity rates indoors and outdoors when compared to the placebo. CONCLUSION: Evidence demonstrating that Anopheles vectors bite both indoors and outdoors indicates that currently implemented indoor-based vector control tools may not be sufficient to eliminate malaria. The documented impact of the SR intervention on Aedes, Armigeres and Culex species points to its importance in combatting other vector borne diseases. Studies to determine the impact of spatial repellents on other mosquito-borne diseases is recommended.

Community-level impacts of spatial repellents for control of diseases vectored by Aedes aegypti mosquitoes.

Spatial repellents (SRs) reduce human-mosquito contact by preventing mosquito entrance into human-occupied spaces and interfering with host-seeking and blood-feeding. A new model to synthesize experimental data on the effects of transfluthrin on Aedes aegypti explores how SR effects interact to impact the epidemiology of diseases vectored by these mosquitoes. Our results indicate that the greatest impact on force of infection is expected to derive from the chemical's lethal effect but delayed biting and the negative effect this may have on the mosquito population could elicit substantial impact in the absence of lethality. The relative contributions of these effects depend on coverage, chemical dose, and housing density. We also demonstrate that, through an increase in the number of potentially infectious mosquito bites, increased partial blood-feeding and reduced exiting may elicit adverse impacts, which could offset gains achieved by other effects. Our analysis demonstrates how small-scale experimental data can be leveraged to derive expectations of epidemiological impact of SRs deployed at larger scales.

Knowledge, attitudes and practices assessment of malaria interventions in rural Zambia.

BACKGROUND: Despite rapid upscale of insecticide-treated nets (ITNs) and indoor residual spraying (IRS), malaria remains a major source of morbidity and mortality in Zambia. Uptake and utilization of these and novel interventions are often affected by knowledge, attitudes and practices (KAP) amongst persons living in malaria-endemic areas. The aims of this study were to assess malaria KAP of primary caregivers and explore trends in relation to ITN use, IRS acceptance and mosquito density in two endemic communities in Luangwa and Nyimba districts, Zambia. METHODS: A cohort of 75 primary caregivers were assessed using a cross-sectional, forced-choice malaria KAP survey on ITN use, IRS acceptance and initial perception of a novel spatial repellent (SR) product under investigation. Entomological sampling was performed in participant homes using CDC Miniature Light Traps to relate indoor mosquito density with participant responses. RESULTS: Ninety-nine percent of participants cited bites of infected mosquitoes as the route of malaria transmission although other routes were also reported including drinking dirty water (64%) and eating contaminated food (63%). All caregivers agreed that malaria was a life-threatening disease with the majority of caregivers having received malaria information from health centers (86%) and community health workers (51%). Cumulatively, self-reported mosquito net use was 67%. Respondents reportedly liked the SR prototype product but improvements on color, shape and size were suggested. Overall, 398 mosquitoes were captured from light-trap collections, including 49 anophelines and 349 culicines. Insecticide treated nets use was higher in households from which at least one mosquito was captured. CONCLUSIONS: The current study identified misconceptions in malaria transmission among primary caregivers indicating remaining knowledge gaps in educational campaigns. Participant responses also indicated a misalignment between a low perception of IRS efficacy and high stated acceptance of IRS, which should be further examined to better understand uptake and sustainability of other vector control strategies. While ITNs were found to be used in study households, misperceptions between presence of mosquitoes and bite protection practices did exist. This study highlights the importance of knowledge attitudes and practice surveys, with integration of entomological sampling, to better guide malaria vector control product development, strategy acceptance and compliance within endemic communities.

[Response of Aedes aegypti L. (Diptera: Culicidae) to transfluthrin and linalool impregnated in different of fabric types.] / Respuesta de Aedes aegypti L. (Diptera: Culicidae) a transflutrina y linalol impregnados en diferentes tipos de tela.

OBJECTIVE: Evaluate the effect of spatial repellency against Ae. aegypti of two chemical compounds impregnated in different types of fabrics. MATERIALS AND METHODS: The study was carried out in the year 2015-2016 in the Centro Regional de Investigación en Salud Pública, del Instituto Nacional de Salud Pública. The high-throughput screening system was used to evaluate the response of Ae. aegypti to transfluthrin and linalool, impregnated individually at different concentrations in poplin, cotton and polyester. The effect of their mixtures was also determined, washing on residuality and percentage of protection. RESULTS: The highest spatial repellency response was for 0.1% linalool-cotton treatment (RE = 70 ± 5.77%). The mixture of 0.1% linalool and 0.001% transfluthrin presented a similar spatial repellence percentage for the three types of fabric. The transfluthrin-poplin treatment 0.001% maintained a residual of five days. 0.1% linalool produced a 62.50% protection in the presence of an attraction stimulus. CONCLUSIONS: It is suggested the impregnation of 0.1% linalool in clothing as a protection measure for Ae. aegypti.

OBJETIVO: Evaluar el efecto de repelencia espacial contra Ae. aegypti de dos compuestos químicos impregnados en diferentes tipos de telas. MATERIAL Y MÉTODOS: El estudio se realizó en el periodo 2015-2016 en el Centro Regional de Investigación en Salud Pública, del Instituto Nacional de Salud Pública. Se utilizó el Sistema de Procesamiento de Alto-rendimiento para evaluar la respuesta de Ae. aegypti a transflutrina y linalol, impregnados individualmente a diferentes concentraciones en popelina, algodón y poliéster. También se determinó el efecto de sus mezclas, lavado sobre la residualidad y porcentaje de protección. RESULTADOS: La mayor respuesta de repelencia espacial fue para el tratamiento linalol-algodón al 0.1% (RE= 70 ± 5.77%). La mezcla de linalol 0.1% y transflutrina 0.001% presentóun porcentaje de repelencia espacial similar para los tres tipos de tela. El tratamiento transflutrina-popelina 0.001%N mantuvo una residualidad de cinco días. El linalol al 0.1% produjo 62.50% de protección en presencia de un estímulo de atracción. CONCLUSIONES: Se sugiere la impregnación de linalol al 0.1% en ropa como medida de protección de las picaduras de Ae. aegypti.

Fipronil and ivermectin treatment of cattle reduced the survival and ovarian development of field-collected Anopheles albimanus in a pilot trial conducted in northern Belize.

BACKGROUND: Most malaria vector control programmes rely on indoor residual spraying of insecticides and insecticide-treated bed nets. This is effective against vector species that feed indoors at night and rest inside the house afterwards. In Central America, malaria vectors have different behaviours and are typically exophagic (i.e., bite outdoors), exophilic (i.e., remain outdoors after feeding), and zoophagic (i.e., as likely to feed on non-humans as humans). Thus, malaria elimination in Central America may require additional tactics. This pilot study investigated whether commercially-available products used to treat livestock for ticks could also be used to kill and/or sterilize zoophagic malaria vectors that feed on treated cattle in Belize. METHODS: Cattle were treated with either a pour-on formulation of 1% fipronil (3 heifers) or injection of 1% ivemectin (1 heifer). Control heifers (n = 2) were left untreated. Field-collected Anopheles albimanus contained in screen-top cages were strapped onto cattle at 2, 5, 7, and 14 days after treatment. Mosquito mortality was monitored once a day for 4 successive days. Surviving mosquitoes were dissected to assess blood meal digestion and ovarian development. RESULTS: A total of 1078 female An. albimanus mosquitoes were fed and monitored for mortality. Both fipronil and ivermectin significantly reduced survivorship of An. albimanus for up to 7 days after treatment. By 14 days, efficacy had declined. The ivermectin treatment completely lost its effectiveness and even though the fipronil-treated heifers were still killing significantly more mosquitoes than the untreated heifers, the amount of mosquito killing had diminished greatly. Both treatments significantly reduced ovary development in mosquitoes fed on treated cattle for the duration of the 2-week trial. CONCLUSIONS: Treatment of cattle in northern Belize with topical fipronil and injectable ivermectin had significant lethal and sublethal effects on wild An. albimanus females. These results suggest that efforts towards eliminating residual transmission of malaria by zoophagic vectors in Central America may benefit by the judicious, targeted treatment of livestock with mosquitocidal compounds, such as fipronil or ivermectin.

The field evaluation of a push-pull system to control malaria vectors in northern Belize, Central America.

BACKGROUND: Campaigns for the continued reduction and eventual elimination of malaria may benefit from new and innovative vector control tools. One novel approach being considered uses a push-pull strategy, whereby spatial repellents are used in combination with outdoor baited traps. The desired effect is the behavioural manipulation of mosquito populations to elicit movement of vectors away from people and into traps. METHODS: Here, a prototype push-pull intervention was evaluated using an experimental hut methodology to test proof-of-principle for the strategy against two natural vector populations, Anopheles albimanus and Anopheles vestitipennis, in Belize, Central America. A Latin square study design was used to compare mosquito entry into experimental huts and outdoor traps across four different experimental conditions: 1) control, with no interventions; 2) pull, utilizing only outdoor traps; 3) push, utilizing only an indoor spatial repellent; and 4) push-pull, utilizing both interventions simultaneously. RESULTS: For An. vestitipennis, the combined use of an indoor repellent and outdoor baited traps reduced average nightly mosquito hut entry by 39% (95% CI: [0.37-0.41]) as compared to control and simultaneously increased the nightly average densities of An. vestitipennis captured in outdoor baited traps by 48% (95% CI: [0.22-0.74]), compared to when no repellent was used. Against An. albimanus, the combined push-pull treatment similarly reduced hut entry, by 54% (95% CI: [0.40-0.68]) as compared to control; however, the presence of a repellent indoors did not affect overall outdoor trap catch densities for this species. Against both anopheline species, the combined intervention did not further reduce mosquito hut entry compared to the use of repellent alone. CONCLUSIONS: The prototype intervention evaluated here clearly demonstrated that push-pull strategies have potential to reduce human-vector interactions inside homes by reducing mosquito entry, and highlighted the possibility for the strategy to simultaneously decrease human-vector interactions outside of homes by increasing baited trap collections. However, the variation in effect on different vectors demonstrates the need to characterize the underlying behavioral ecology of target mosquitoes in order to drive local optimization of the intervention.

A comparison of two commercial mosquito traps for the capture of malaria vectors in northern belize, central america.

To achieve maximum success from any vector control intervention, it is critical to identify the most efficacious tools available. The principal aim of this study was to evaluate the efficacy of 2 commercially available adult mosquito traps for capturing Anopheles albimanus and An. vestitipennis, 2 important malaria vectors in northern Belize, Central America. Additionally, the impact of outdoor baited traps on mosquito entry into experimental huts was assessed. When operated outside of human-occupied experimental huts, the Centers for Disease Control and Prevention (CDC) miniature light trap, baited with human foot odors, captured significantly greater numbers of female An. albimanus per night (5.1 ± 1.9) than the Biogents Sentinel™ trap baited with BG-Lure™ (1.0 ± 0.2). The 2 trap types captured equivalent numbers of female An. vestitipennis per night, 134.3 ± 45.6 in the CDC trap and 129.6 ± 25.4 in the Sentinel trap. When compared to a matched control hut using no intervention, the use of baited CDC light traps outside an experimental hut did not impact the entry of An. vestitipennis into window interception traps, 17.1 ± 1.3 females per hour in experimental huts vs. 17.2 ± 1.4 females per hour in control huts. However, the use of outdoor baited CDC traps did significantly decrease the entry of An. albimanus into window interception traps from 3.5 ± 0.5 females per hour to 1.9 ± 0.2 females per hour. These results support existing knowledge that the underlying ecological and behavioral tendencies of different Anopheles species can influence trap efficacy. Furthermore, these findings will be used to guide trap selection for future push-pull experiments to be conducted at the study site.

Experimental hut and field evaluation of a metofluthrin-based spatial repellent against pyrethroid-resistant Anopheles funestus in Siaya County, western Kenya.

BACKGROUND: Spatial repellents (SR) may complement current vector control tools and provide additional coverage when people are not under their bednets or are outdoors. Here we assessed the efficacy of a metofluthrin-based SR in reducing exposure to pyrethroid-resistant Anopheles funestus in Siaya County, western Kenya. METHODS: Metofluthrin was vaporized using an emanator configured to a liquid petroleum gas (LPG) canister, placed inside experimental huts (phase 1) or outdoors (phase 2), and evaluated for reductions in human landing rate, density, knockdown and mortality rates of An. funestus, which are present in high density in the area. To demonstrate the mosquito recruiting effect of LPG, a hut with only an LPG cooker but no metofluthrin was added as a comparator and compared with an LPG cooker burning alongside the emanator and a third hut with no LPG cooker as control. Phase 2 evaluated the protective range of the SR product while emanating from the centre of a team of mosquito collectors sitting outdoors in north, south, east and west directions at 5, 10 and 20 feet from the emanating device. RESULTS: Combustion of LPG with a cook stove increased the density of An. funestus indoors by 51% over controls with no cook stove. In contrast, huts with metofluthrin vaporized with LPG combustion had lower indoor density of An. funestus (99.3% less than controls), with knockdown and mortality rates of 95.5 and 87.7%, respectively, in the mosquitoes collected in the treated huts. In the outdoor study (phase 2), the outdoor landing rate was significantly lower at 5 and 10 feet than at 20 feet from the emanator. CONCLUSIONS: Vaporized metofluthrin almost completely prevented An. funestus landing indoors and led to 10 times lower landing rates within 10 feet of the emanator outdoors, the first product to demonstrate such potential. Cooking with LPG inside the house could increase exposure to Anopheles mosquito bites, but the use of the metofluthrin canister eliminates this risk.

Comparison of Aedes aegypti (Diptera: Culicidae) resting behavior on two fabric types under consideration for insecticide treatment in a push-pull strategy.

Aedes aegypti (L.), the primary vector of dengue and dengue hemorrhagic fever, breeds and rests predominately inside human dwellings. With no current vaccine available, vector control remains the mainstay for dengue management and novel approaches continue to be needed to reduce virus transmission. This requires a full understanding of Ae. aegypti ecology to design effective strategies. One novel approach is the use of contact irritants at target resting sites inside homes to make the surface unacceptable and cause vectors to escape before biting. The objective of the current study was to observe indoor resting behavior patterns of female Ae. aegypti within experimental huts in response to two fabrics under consideration for insecticide treatment: cotton and polyester. Results indicate that fabric type, coverage ratio of dark to light fabric and placement configuration (vertical vs. horizontal) all influenced the resting pattern of mosquito cohorts. Findings from this study will guide evaluations of a push-pull strategy designed to exploit contact irritant behaviors and drive Ae. aegypti out of homes prefeeding.

Comparison of experimental hut entrance and exit behavior between Anopheles darlingi from the Cayo District, Belize, and Zungarococha, Peru.

Anopheles darlingi is a major vector for malaria in Central and South America. Behavioral, ecological, genetic, and morphologic variability has been observed across its wide distribution. Recent studies have documented that 2 distinct genotypes exist for An. darlingi: a northern lineage (Belize, Guatemala, Colombia, Venezuela, and Panama) and a southern lineage (Amazonia and southern Brazil). In order to determine if these genotypes exhibited different behavioral traits, entrance and exit movement patterns between 2 field populations of An. darlingi that represented each genotype were evaluated using experimental huts. The Belize population exhibited bimodal entrance, with peak entry occurring between 7:00-8:00 p.m. and 5:00-6:00 a.m. and peak exiting occurring between 7:00-8:00 p.m. The Peru population exhibited unimodal entrance, with peak entry occurring between 10:00-11:00 p.m. and peak exiting occurring between 11:00-12:00 a.m. with a secondary smaller peak at 2:30 a.m. Entrance and exit behavioral patterns were significantly different between the Belize and Peru populations of An. darlingi (log-rank [Mantel-Cox] P < 0.001). Information from the present study will be used in the future to determine if there is a correlation between genotype and host-seeking behavior and can be used in the present for regional vector risk assessment.

First record and demonstration of a southward expansion of Aedes albopictus into Orange Walk Town, Belize, Central America.

The first record of Aedes albopictus in northern Belize was made in Orange Walk Town, Orange Walk District, on November 3, 2011. Aedes spp. larvae were collected during a routine Ministry of Health mosquito survey and reared to adults. Upon emergence, a mixed population of Aedes aegypti (35) and Ae. albopictus (11) was observed (aegypti:albopictus = 3:1). Subsequent larval and adult surveys in Orange Walk and Corozal District, also in northern Belize, have confirmed the presence of Ae. albopictus, thereby indicating the range expansion and establishment of this nuisance biter and potential disease vector in Belize.

A cluster-randomized, placebo-controlled trial to evaluate the efficacy of a spatial repellent (Mosquito Shield™) against Aedes-borne virus infection among children ≥ 4-16 years of age in the Gampaha District, Sri Lanka: study protocol (the AEGIS program).

BACKGROUND: Spatial repellents (SRs) have been widely used for prevention of mosquito bites, but their efficacy in reducing Aedes-borne viruses (ABV) has not been tested rigorously at large scale in Asia. To address this knowledge gap, a trial to evaluate the efficacy of Mosquito Shield™, a transfluthrin SR, was developed in Gampaha District of Sri Lanka across three Medical Officer of Health areas; i.e., Negombo, Wattala, and Kelaniya. METHODS: This trial is a cluster-randomized, placebo-controlled, double-blinded clinical trial. A total of ~14,430 subjects aged ≥ 6 months in 30 clusters (15 intervention, 15 placebo) from ~3900 households (HH) will be randomly selected for enrolment into a "febrile surveillance cohort." A subset of the surveillance cohort, ~3570 subjects aged ≥4-16 years that test seronegative (naïve) or are serologically positive for a previous single dengue virus (DENV) infection (monotypic) at baseline sampling, will be enrolled into a "longitudinal cohort" for measuring DENV infection based on laboratory-confirmed seroconversion during the trial. Persons identified positive for antibodies against multiple DENV serotypes (multitypic) at baseline will be monitored for secondary analyses. Active ABV disease will be assessed using an enhanced passive surveillance system with case ascertainment performed in designated healthcare facilities. Serum samples will be taken from longitudinal cohort subjects within 1-2 weeks of when intervention is first deployed (T0) with additional samples taken ~12 (T1) and ~24 months (T2) from baseline sampling. DENV seroconversion and ABV active disease rates from baseline (pre-intervention) and follow-up (post-intervention) samples will be compared between intervention and placebo clusters. Participating houses will be monitored entomologically (indoor adult Aedes aegypti population densities and adult female blood fed status) within 3 months before intervention deployment and monthly during the intervention phase. Entomological surveys will monitor indoor adult Ae. aegypti population densities and blood fed status. Dengue incidence in each cohort will be estimated and compared to determine the public health benefit of using an SR. Entomological parameters will be measured to determine if there are entomological correlates of SR efficacy that may be useful for the evaluation of new SR products. DISCUSSION: The trial will serve as an efficacy assessment of SR products in South Asia. Results will be submitted to the World Health Organization Vector Control Advisory Group for assessment of public health value towards an endorsement to recommend inclusion of SRs in ABV control programs. TRIAL REGISTRATION: Sri Lanka Clinical Trial Registry SLCTR /2022/018. Registered on July 1, 2022. CLINICALTRIALS: gov NCT05452447 . Registered on July 11, 2022. The Universal Trial Number is U1111-1275-3055.

Altitude, not potential larval habitat availability, explains pronounced variation in Plasmodium falciparum infection prevalence in the western Kenya highlands.

Progress in malaria control has stalled over the recent years. Knowledge on main drivers of transmission explaining small-scale variation in prevalence can inform targeted control measures. We collected finger-prick blood samples from 3061 individuals irrespective of clinical symptoms in 20 clusters in Busia in western Kenya and screened for Plasmodium falciparum parasites using qPCR and microscopy. Clusters spanned an altitude range of 207 meters (1077-1284 m). We mapped potential mosquito larval habitats and determined their number within 250 m of a household and distances to households using ArcMap. Across all clusters, P. falciparum parasites were detected in 49.8% (1524/3061) of individuals by qPCR and 19.5% (596/3061) by microscopy. Across the clusters, prevalence ranged from 26% to 70% by qPCR. Three to 34 larval habitats per cluster and 0-17 habitats within a 250m radius around households were observed. Using a generalized linear mixed effect model (GLMM), a 5% decrease in the odds of getting infected per each 10m increase in altitude was observed, while the number of larval habitats and their proximity to households were not statistically significant predictors for prevalence. Kitchen located indoors, open eaves, a lower level of education of the household head, older age, and being male were significantly associated with higher prevalence. Pronounced variation in prevalence at small scales was observed and needs to be taken into account for malaria surveillance and control. Potential larval habitat frequency had no direct impact on prevalence.