A review of selective indoor residual spraying for malaria control

A review of selective indoor residual spraying for malaria control | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Systematic Review A review of selective indoor residual spraying for malaria control Seth Irish, Derric Nimmo, Jameel Bharmel, Frederic Tripet, Pie Müller, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4230947/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 23 Aug, 2024 Read the published version in Malaria Journal → Version 1 posted 8 You are reading this latest preprint version Abstract Background Indoor residual spraying (IRS) is one of the most effective malaria control tools. However, its application has become limited to specific contexts due to the increased costs of IRS products and implementation programs. Selective spraying – selective spray targeted to particular areas/surfaces of dwellings – has been proposed to maintain the malaria control and resistance-management benefits of IRS while decreasing the costs of the intervention. Methods A literature search was conducted to find 1) studies that assessed the resting behaviour of Anopheles mosquitoes and 2) studies that evaluated the impact of selective spraying on entomological and malaria outcomes. Additional articles were identified through hand searches of all references cited in articles identified through the initial search. A cost model was developed from PMI VectorLink IRS country programs, and comparative cost analysis reports to analyze the overall cost benefits of selective IRS. Results In some studies, there appeared to be a clear resting preference for certain Anopheles species in terms of the height at which they rested. However, for other species, and particularly the major African malaria vectors, a clear resting pattern was not detected. Furthermore, resting behavior was not measured in a standardized way. For the selective spray studies that were assessed, there was a wide range of spray configurations, which complicates the comparison of methods. Many of these spray techniques were effective and resulted in reported 25-68% cost savings and reduced use of insecticide. The reported cost savings in the literature do not always consider all of the IRS implementation costs. Using the IRS cost model, these savings ranged from 17-29% for programs that targeted Anopheles sp. and 18-41% for programs that targeted Aedes aegypti . Conclusions Resting behavior is generally measured in a simplistic way; noting the resting spot of mosquitoes in the morning. This is likely an oversimplification, and there is a need for better monitoring of resting mosquitoes. This may improve the target surface for selective spray techniques, which could reduce the cost of IRS while maintaining its effectiveness. Reporting of cost savings should be calculated considering the entire implementation costs, and we provide a cost model for future calculations. selective spraying partial spraying indoor residual spraying resting Anopheles malaria Figures Figure 1 Figure 2 Introduction Malaria continues to cause high levels of morbidity and mortality, particularly in Africa, where the majority of malaria cases occur (WHO 2023). In 2022, malaria cases increased to an estimated 249 million cases, resulting in an estimated 608,000 deaths (WHO 2023). To decrease the number of cases, it is important to invest in effective testing and treatment of malaria, as well as undertaking strategies that prevent malaria transmission. Vector control is the most effective current malaria prevention strategy, and the main techniques employed are the distribution of insecticide-treated nets (ITNs) and indoor residual spraying (IRS). In recent years, there has been the development of highly effective nets with different active ingredients (e.g. Mosha et al. 2023; Protopopoff et al. 2018). This has resulted in some countries stopping their IRS programs, partly due to cost considerations, even though IRS remains highly cost effective (Oxborough 2016; Yukich et al. 2022). However, IRS has several advantages which might be useful if the costs of IRS could be reduced. These advantages include the possibility for insecticide rotation as part of a resistance management plan (WHO 2012), less necessity for active utilization (as compared to ITNs, which must be put in place by homeowners each night) (Monroe et al. 2021), and, similar to ITNs, IRS can have a community protection effect when coverage is high (Rehman et al. 2011). One way to decrease the cost of IRS is through selective indoor spraying of some of the surfaces in houses. It should be noted that selective spraying is sometimes termed “targeted IRS” (Manrique-Saide et al. 2020) or “partial IRS” (Coleman et al. 2021) that should be distinguished from the targeted application of IRS to areas where there is evidence of recent malaria transmission rather than blanket application to all houses (Bath et al. 2021). Conventional IRS recommended by WHO for malaria control (WHO 2023) involves the full spraying of all indoor walls and often the ceilings of houses. Optimally, the selective indoor spray is applied where mosquitoes are most likely to rest (WHO 2023). Selectively applying residual insecticides, e.g., for Aedes aegypti on exposed lower sections of walls (< 1.5 m), under furniture, and on dark surfaces throughout houses provides an entomological impact similar to spraying entire walls (as performed in classic IRS), but in a fraction of the time (< 18%) and insecticide volume (< 30%) compared to classic IRS (Manrique-Saide et al. 2020). Other studies have shown important impacts using selective spraying (Vazquez-Prokopec et al. 2022; Karstein et al. 2023). This selective spraying approach is endorsed by the Pan American Health Organization for IRS spraying for control of Aedes aegypti in urban settings (PAHO 2019). While numerous studies have been done to evaluate selective IRS for malaria control, this work has not provided conclusive findings required to change current policies. This narrative review summarizes previous research on the use of selective spraying for vector-borne disease control and the cost-saving implications to see whether there might be justification for the use of selective spraying for malaria control, and to determine what avenues of research might be the most impactful to maximize its efficacy. Materials and methods Selection criteria Studies were included if they considered the two key questions of this review: resting behavior of Anopheles mosquitoes or efficacy of selective indoor residual spraying. Search strategy An initial search was conducted on PubMed in July 2022, without language or date limits to find 1) studies that assessed the resting behaviour of Anopheles mosquitoes and 2) studies that evaluated the impact of selective spraying on entomological and malaria outcomes. Search terms included “partial indoor residual spraying” and “targeted indoor residual spraying”. Additional articles were identified through hand searches of all references cited in articles identified through the initial search. This process continued until no further related articles were found. Data extraction Data from the selected papers were extracted to determine the resting heights and behaviors of Anopheles mosquitoes. Additionally, data was extracted from articles that discussed the impact of selective spraying, and the impact and cost savings of these studies were summarized. Cost analysis A cost model was constructed from the PMI VectorLink IRS country programs comparative cost analysis reports. The model is based mainly on the 2018 data across the 14 countries where PMI VectorLink performed IRS (Johns et al. 2019). A comparison to the cost analysis data from 2019-2022 shows that the relative cost breakdown for each area has not changed significantly (data not shown). The spray campaign costs were broken down further using the following data and assumptions. Training costs were calculated from the average percentage spray campaign costs used for Malawi, Rwanda and Uganda for training of trainers and SOP and team leader training (data provided by PMI VectorLink). Spray campaign personnel costs were calculated from the total campaign days and the daily wages minus the training costs. The rest of the spray campaign costs were assigned to transportation of spray personnel (mainly vehicle hire, drivers and fuel). Results The main results from this review were separated into two categories, 1) description of the resting sites of mosquitoes inside houses and 2) reports of experiments or operational pilots of selective spraying. Seventeen studies were found reporting the resting sites of mosquitoes in houses, and nine were found reporting on experiments or pilot studies of selective spraying. Resting sites of mosquitoes in houses Resting height The results collated from the reviewed publications showed clear evidence that the resting sites and behavior of the mosquitoes vary. These variations were observed both between and occasionally within species. In many of the publications, the height (distance above the floor) at which mosquitoes were collected was reported. Based on these data, it was determined that Anopheles darlingi , Anopheles aquasalis, Anopheles ludlowi, Anopheles hyrcanus, Anopheles fluviatilis, Anopheles leucosphyrus, Anopheles aconitus, Anopheles kochi, Anopheles subpictus, Anopheles indefinitus, Anopheles marajoara , Anopheles punctimacula, Anopheles nuneztovari , and Anopheles flavirostris tended to rest primarily on the lower half of walls (Deane & Damasceno 1948, Chow et al. 1951, Russell 1963, Elliott 1972, Damar et al. 1981, Quiñones & Suarez 1990, Asinas et al. 1994). In contrast, Anopheles barbirostris , Anopheles oswaldi , and Anopheles rangeli were found to rest above 1.5m above the floor, and often higher (Damar et al. 1981, Quiñones & Suarez 1990). Sahu et al. (2011) found 99% of Anopheles minimus and Anopheles fluviatilis to rest on walls (as opposed to eaves, hanging objects, and the roof), with most of these mosquitoes resting between 90-125 cm from the ground. It is important to note that most of these studies were conducted outside of Africa. Despite this, a few key studies based in Africa have investigated the resting behavior of Anopheles gambiae s.l. and Anopheles funestus vectors . These studies can largely be grouped into monitoring the height of the resting site on the wall or roof, additional observations about the substrate on which mosquitoes rest, and their resting behaviour conducted within experimental huts were also noted. In his first study looking at the resting height of malarial vectors, Smith (1955) investigated the distribution of An. gambiae and An. funestus vectors in cone huts on Ukara Island (a Tanzanian island in Lake Victoria, near Mwanza). These cone huts measured 6.4m high and 6.9m wide at their bases, and typically housed both humans and cattle. The huts were searched until all observable mosquitoes had been collected and their location of collection was recorded. From the trial it was shown that the vast majority of female mosquitoes (80% of An. gambiae and 79% of An. funestus ) were found to be resting below 2.1m (from the floor) in the huts during the rainy season. The majority of these rested on the human-habited side of the huts; nevertheless, considerable numbers were also found on the cattle-habited side of the huts. The same trend was found during the dry season. Later, Smith (1962) collected mosquitoes from houses of three different types ( tembe , msonge , and banda ) in Tanzania. Initial catches were conducted between 0800-1200 with additional complementary catches between 1100-1500 being conducted three days later. During the collection period, the proportion of An. gambiae mosquitoes resting on the roof ranged from 42% to 74%. There were no large differences between the proportions resting on the roof during the night and day, but there were differences in roof-resting between the different types of huts. Mathis et al. (1963) reported 94.6% of An. gambiae and An. funestus were collected on the ceilings in monitored huts. On the contrary, Mutinga et al. (1995) noted An. gambiae mosquitoesresting primarily on the lower parts of walls and the darker parts of the room. Osae (2014) found large proportions of all three species resting above 2m ( An. gambiae : 76%, Anopheles coluzzii 58%, An. funestus 74%), and preferably on dark materials in cool, humid areas. Sande et al. (2016) found the highest proportion of An. funestus and An. gambiae on the roof (although considerable numbers were found on walls, with fewer mosquitoes collected on furniture. When only wall surfaces were considered, the majority were collected below 1 meter (44% of An. funestus , 64% of An. gambiae s.l. ). Msugupakulya et al. (2020) evaluated the resting sites of An. gambiae and An. funestus in different types of houses. They found that the highest numbers of mosquitoes rested on the roof in houses with thatched roofs (with the exception of An. funestus in brick houses), and in houses with metal roofs, the highest numbers of mosquitoes rested on surfaces other than walls or roofs. It is worth noting that in all types of houses, mosquitoes were found resting on walls, roofs, and other surfaces (Table 1). Resting substrate Other studies have looked at the effect of resting substrate or other factors on the resting behavior of African malaria vectors. Smith (1962) evaluated the impact of different factors within experimental huts to evaluate their impact on mosquito resting behavior. He found that neither building a partition wall in the hut, modifying the hut entry site, adding a ceiling, modifying the surface of the roof, nor the abdominal status (or source of blood meal) appeared to change the resting behavior of An. gambiae in terms of resting on the roof or walls. However, modifying the substrate of the walls (from smooth mud to rough mud) resulted in greater resting on rough mud walls. Similarly, making a fire inside the huts resulted in decreased resting on the roof and increased resting on walls. Beds were not a major resting site for mosquitoes in experimental huts, with only nine percent of mosquitoes collected from beds. Mutinga et al. (1995) found that An. gambiae preferred to rest on fabric attached to the walls. Osae found differences in resting sites between An. gambiae , An. coluzzii , and An. funestus in Ghana (2014). He found the main resting sites to be roofing beams for An. gambiae (28%), on netting or frames of windows for An. coluzzii (20%), and for An. funestus, it was the roof. He also looked at the materials that mosquitoes were resting, with An. gambiae and An. funestus resting primarily on wood surfaces, and An. coluzzii resting on nylon. Resting sites of mosquitoes in experimental huts Finally, some studies taking place in experimental huts have monitored the resting behavior prior to introducing interventions such as wall spraying. Smith (1962) found higher proportions of An. gambiae resting on the roof in experimental huts than in other types of structures, with 94-97% of mosquitoes resting on roofs, compared with 42-74% in local houses. Coleman et al. (2021) monitored the resting sites of An. gambiae s.l. collected in West African experimental huts in Ghana. The majority of An. gambiae s.l. were collected from the ceiling and the top half of the veranda. In a follow up study, Chabi et al. (2023) found 43% of An. gambiae s.l. resting on the lower half of walls, 24% of mosquitoes resting on the top half of walls, and 33% of mosquitoes resting on ceiling. Evaluation of selective spraying In the first year of the “Sardinian Project” an attempt to eliminate Anopheles labranchiae from Sardinia, selective spraying was conducted with spraying of walls below 1.5m in the first campaign (1946-1947), but in successive campaigns “full spraying” was conducted (Logan 1953). Malaria cases declined from 74,641 in the first year (1946) to 39,303 in the second (Tognotti 2009), although the impact of selective spraying with DDT cannot be disentangled from the impact of large-scale aerial adulticide/larvicide application and source reduction that was carried out in parallel. This highlights the previous/historical use of selective IRS, however, no further details on impact of the intervention were provided in this source. Another method of selective spraying was evaluated in Lebanon (Gramiccia 1953), where “band spraying” was attempted, spraying horizontal swaths of DDT of 30cm width separated by an equal distance of unsprayed areas (all 1m above the ground). The impact of this type of spraying was measured in areas where Anopheles sacharovi and Anopheles superpictus were the main vectors both by looking at malaria rates, and collection of Anopheles in houses in areas where full spraying or selective spraying had been conducted (relative to control areas). While no impact on parasite rates was found, due to a drop in cases in both control and treatment areas, there was a reduction in Anopheles in the full and selectively sprayed houses. The authors estimated the cost savings that might be found with selective spraying was approximately 31.3% (including the costs of DDT, labor, transport, storage, etc.) (Table 2). Pletsch and Demos (1954) reported “selective spraying” in Taiwan against Anopheles minimus . Full spraying was conducted by spraying walls, roofs, ceilings, and undersides of furniture with DDT (2g/m 2 ). The inner walls and undersides of roofs of all outbuildings were also sprayed except for the first 50cm of the wall in pig pens. “Selective spraying” was done in several ways; on the walls of bedrooms and storerooms, the underside of the roof in bedrooms, the ceilings in bedrooms and storerooms (which were quite rare), the undersides of furniture and window recesses in bedrooms, storerooms, sitting rooms, and kitchens (only inside and under the food cabinet), and the underside of the bed or bed platform in bedrooms. Any room in which people slept was considered a bedroom. The results from two rounds of both spray types were positive, reducing malaria rates from over 20% to less than 1% in Chi-Shan, and reducing them from about 2% to 0% in an additional study in central Taiwan. Both entomological investigations supported the finding of effective control and reduction of the numbers of mosquitoes collected in bedrooms to zero with both techniques. The cost savings were generated from spraying 38.4% less surface area in the selective spraying treatment, and the overall costs were reduced by 25.6%. However, some disadvantages of selective spraying were noted, specifically, the detection of An. minimus mosquitoes in cattle sheds (a possible harborage that could result in the build-up of resistance), the detection of Anopheles sinensis in cattle sheds that bothered the farmers’ water buffalo, and hesitation from homeowners and sprayers about receiving less than full coverage. Gandahusada et al. (1984) built on the knowledge about Anopheles aconitus resting sites to evaluate full and selective spraying in Java, Indonesia, using fenitrothion as An. aconitus populations were becoming resistant to DDT. They designed three areas for the study, one for full spraying, one for selective spraying (between 10 and 85cm on the wall, in addition to full spraying of cattle shelters), and one for the control. Cholinesterase levels were monitored in the sprayers to prevent negative health effects from exposure to the insecticide. More sprayers in the full spray arm had >50% reduction in cholinesterase than those in the selective spray arm, indicating less exposure for those conducting the selective spray. The full spray arm reduced malaria slide-positive rates from 6.5% to 0.4%, while selective spray reduced the rate from 1.9% to 0.3%. However, there was a more substantial decrease in the Plasmodium falciparum index (proportion of cases caused by P. falciparum ) in the full coverage area than in the selective spray area. Asinas et al. (1994) observed resting heights of Anopheles flavirostris in a site outside of Manila, Philippines. They found the vast majority resting below 1m on the walls and evaluated the impact of selective spraying (the lower 70cm of the wall, as well as 10cm around windows and interior and exterior eaves) in experimental huts for 6 months. They found similar results for full spraying and selective spraying, with never more than an 8% difference in mosquito mortality between the two. Arredondo Jiménez et al. (1995) evaluated full spraying and selective spraying (a horizontal swath on the wall between 0.75 and 1.75m from the floor, as well as a 1m swath of the roof from where it met the wall) with bendiocarb in Mexico. They followed the community for two years (over four spray rounds) and measured the entomological impact. They did not note substantial differences between the fully sprayed and selectively sprayed areas in terms of residual activity of the insecticide, resting behavior or mortality of An. albimanus mosquitoes, or human landing collections. They found a 50% savings in spraying time in the selective spray area and 40% overall cost savings. Coleman et al. (2021) conducted an experimental hut study coupled with a village-level study to evaluate selective spraying. The experimental hut study evaluated half walls (lower and upper) in combination with the ceiling with full spraying. There was no significant difference in mortality of An. gambiae s.l. found between full spraying and either of the selective spraying treatments. The inclusion of the ceiling appeared to be important, as the mortality was more than 20% higher when the ceiling was included in the treatment arms. There was also no significant difference between human biting rates between full and selectively sprayed communities (upper half+ceiling), and both were significantly lower than in unsprayed communities. Chabi et al. (2023) conducted an experimental hut trial in Côte d’Ivoire, in an area of intense pyrethroid resistance. Three IRS insecticides (pirimiphos methyl 1g/m 2 (Actellic), clothianidin 300mg/m 2 (SumiShield) and clothianidin 200mg/m 2 +deltamethrin 25mg/m 2 (Fludora Fusion)) were evaluated with four treatments (unsprayed, fully sprayed, bottom half of the wall + ceiling, upper half of wall +ceiling). For all three insecticides, there was slightly higher mortality with the bottom half of the wall+ceiling than the upper half of the wall + ceiling. The differences in mortality between full spray and the two selective spray treatments were not statistically significant except for clothianidin, where the top half+ceiling spray resulted in less mortality than the other two treatments. Snetselaar et al. (in preparation) evaluated selective spraying and uneven spraying in release-recapture and experimental hut studies. In the release-recapture study, Anopheles gambiae Kisumu (susceptible to all insecticides tested) was released in huts with clothianidin 200mg/m2 + deltamethrin 25mg/m2 (Fludora Fusion) sprayed using a selective, checkerboard spray (50% of walls sprayed), uneven spray (some areas sprayed at 10%, others at 100%, and others at 190%), full spray (manual or with a track sprayer), as well as full spraying of pirimithos-methyl 1g/m 2 (Actellic). Mortality (24h) was not significantly different between any of the treatments. For the experimental hut trial with Anopheles arabiensis , the highest 24 hour mortality was found with the track sprayer full spray, and the mortality was not significantly different between the other treatments. IRS program cost analysis The percentage break down of the PMI VectorLink IRS program costs are shown in figure 1. For all of the publications where cost savings of IRS are reported, most authors have shown the data for reduction in insecticide use and spray team costs (mainly staff costs) (Table 2). Coleman et al. (2021) have also extrapolated that a reduction in the spray team time would also reduce the transportation costs by the same percentage, as the team could spray more houses in a day, requiring less travel to complete the same number of houses. Using these assumptions, the IRS cost model was used to show the overall savings that could be achieved when the entire program costs are included, such as admin, monitoring, entomology, and community engagement. An example of the inputs and outputs from the IRS cost model are shown in Figure 2 for the results reported by Coleman et al. (2021). The overall savings when selective IRS was used ranged from 15.5-28.6% for programs which targeted Anopheles mosquitoes and 17.5-41.1% for programs that targeted Ae. aegypti . Discussion Selective spraying has been repeatedly proposed as a solution to optimize the cost effectiveness and minimize the logistical challenges of IRS. Observations of patterns in the resting behavior of mosquitoes have led to the conclusion that if preferred resting places are sprayed, then a comparable impact can be achieved with less (but more targeted) spraying. As several authors have noted, this depends on using a non-irritant insecticide to ensure that mosquitoes do not avoid sprayed areas (Byford et al. 1987, Asinas et al. 1994). From some of the operational pilots and experimental hut studies, it appears that selective spraying can result in comparable results at a reduced cost. Some studies noted epidemiological impacts at reduced costs (Pletsch & Demos 1954, Lassen et al. 1972, Gandahusada et al. 1984), whereas other studies noted important entomological impacts (Gramiccia et al. 1953, Asinas et al. 1994, Arredondo-Jiménez et al. 1995, Coleman et al. 2021, Chabi et al. 2021). In some cases, there appeared to be a slightly reduced effect or other disadvantages such as possible selection of resistance, slower rates of decrease in malaria rates, and reluctance from homeowners (Pletsch & Demos 1954, Gandahusada 1984), whereas in other cases, there appeared to be advantages other than reduced costs, i.e. reduced insecticide exposure (Gandahusada et al. 1984). An essential part of selective spraying is the determination of what parts of houses should be sprayed and what parts of houses should not be sprayed. While in some cases, this decision has been informed by previous work, in other cases, the choice seems to be somewhat arbitrary. The two main factors that could inform selective spraying are logistical (i.e. making spraying houses easier and faster) or behavioral (using the behavior of the mosquito to target the key resting spaces). Aspects of spraying that would reduce the amount of spraying and logistical costs could include: Spraying that can be done from outside houses (i.e. eaves, animal shelters, etc.) Spraying that doesn’t require the movement of furniture (upper halves of walls, ceilings, undersides of furniture), which may additionally benefit from increased user uptake Targeted spraying of houses (ie. Only spraying houses at the edges of a village, near breeding sites or houses with children under five years of age) Aspects of behavior that could result in reduced spraying could include monitoring the resting behavior of mosquitoes as determined through: Rooms in which mosquitoes are resting (bedrooms, kitchens, bathrooms, animal shelters, etc.) The height of resting sites on the wall[1] The type of building in which mosquitoes are resting The amount of light (lux) present in resting site Temperature and humidity of resting sites Air movements The substrate on which mosquitoes are resting (wood, mud, clothes, furniture, etc.)(see Table 3 in Urbino et al. 1961) The interaction between an insecticide and a mosquito (toxicity and irritancy) Resting behavior related to seasonality (Smith 1955) Types of houses (wall substrate, roof material) (Msugupakulya et al. 2020) Orientation (north, east, west, south) with respect to sun, climatic conditions Resting behavior of mosquitoes infected with Plasmodium parasites. As seen above, the behavior of mosquitoes (in combination with an understanding of logistical issues) is essential for understanding the optimal design of a selective spray program. One of the challenges for understanding the resting behavior of mosquitoes is the fact that mosquitoes may move around the inside of houses over the course of the night, but the collection of mosquitoes at dawn may only capture one aspect of this movement. Indeed, when mosquitoes have been collected at different times or monitored through observation, it has been shown that they are moving inside houses to some degree (Smith 1962, Bown et al. 1993). It is likely that mosquitoes balance the need for homeostasis (optimal temperature and humidity) (Verhulst et al. 2020) with a choice of colours and low light to be the least visible. Better methods for monitoring mosquitoes (video recording, motion sensing, collections at multiple times) may allow for better targeting of insecticides. This improved monitoring of resting site behavior would seem especially important for the major African malaria vectors, An. gambiae s.l. and An. funestus , as there appear to be contradictory findings in the literature. The earliest recording of resting heights found most An. gambiae and An. funestus to be resting on walls below 2.1m; however, this was in “cone huts” that reached 6.4m in height (Smith 1955). Mathis et al. (1963) reported that 94.6% of An. gambiae and An. funestus collected in houses were resting on the ceiling. Mutinga et al. (1995) stated that An. gambiae rested primarily on the lower parts of walls, on fabric, and on the dark side of the room. Osae (2014) reported a number of resting sites for An. gambiae , An. coluzzii , and An. funestus . He stated that most of the An. gambiae (56%) and An. funestus (59%) were resting on roofs, roofing beams, and ceilings between 6:00 and 10:00, whereas only 25% of An. coluzzii were found there. Msugupakulya et al. (2020) found very low numbers of An. funestus (16-20%) and An. arabiensis (8-30%) resting under metal roofs, although higher numbers of the two species when roofs were thatched ( An. funestus (33-55%), An. arabiensis (43-50%)). Importantly, they noted that considerable proportions of mosquitoes in all houses were resting on “other surfaces” than walls and roofs, presenting challenges for spraying (although the movement in houses is not to be forgotten). The two most recent experimental hut studies found different results in their pre-spray collections, with the majority of An. gambiae s.s. remaining in huts in northern Ghana being found on the ceiling (followed by the top half of the wall), whereas the An. coluzzii in Côte d’Ivoire were primarily resting on the bottom half of the wall (followed by the ceiling). The apparent difference in behavior might explain why in Côte d’Ivoire, in huts treated with clothianidin, the bottom half + ceiling treatment was more effective than the top half + ceiling treatment. However, there is much to be learned about the behavior of mosquitoes inside houses, and what to do when there are multiple vector species. A better understanding of this behavior will allow the development of better selective spray methods. The potential cost savings of selective IRS could be substantial; and reported savings in the literature range from 38-85% for insecticide use and 25.7-82% for spray team costs (wages and food). The level of cost reduction depends on the type of selective spraying employed. In some cases, the selective spraying was limited to a single band in houses (Gandahusada et al. 1984), whereas in other studies, it was only half of the wall that was excluded (Coleman et al. 2021, Chabi et al. 2023). Reductions in costs can come from reduced insecticide and reduced time required to treat houses, especially if furniture does not have to be removed, including spray pump refilling time, water collection, etc. However, these reported cost savings do not consider other costs typically associated with an IRS control program, such as surveillance and monitoring, administrative staff, chemical storage, environmental assessment, equipment etc. To understand the impact of selective IRS on the total cost of an IRS program, an IRS cost model was developed from cost analysis reports of PMI VectorLink country programs. When considering other IRS program costs and accounting for savings in transport costs not reported in some publications, the overall cost savings ranged from 15.5-28.6% for programs targeting Anopheles mosquitoes . These percentage cost savings could reduce the cost per person per year of a PMI VectorLink IRS program from USD 7.46 (average for 2020-2022) to between USD 5.33 to USD 6.19. These represent substantial cost savings of between 17 and 29%. However, the cost of IRS programs has substantially increased over the past five years, from USD 5.36 per person per year in 2018 to USD 7.69 in 2022, and therefore the impact is substantially reduced due to rising costs (Aghajanyan et al. 2023). Not all IRS programs are run as comprehensively as PMI VectorLink programs, and they may not have all the additional costs besides transport, staff for spraying, and insecticide, which may significantly increase the relative cost advantage of selective IRS. We are unaware of other control programs tracking and publishing their total costs to be able to compare. [1] Note that some of the studies that have measured the resting heights of mosquitoes on walls have not presented data on mosquitoes resting on the ceiling or underside of the roof. Conclusions A clear understanding of mosquito resting behavior is key to the effectiveness of indoor residual spraying, one of the major malaria control interventions. Currently, indoor residual spraying is conducted by spraying all sprayable interior surfaces of a house to maximize the likelihood of a mosquito coming in contact with the insecticide. However, this may not be necessary if mosquitoes preferentially rest on certain surfaces of the house. This review aimed to assess the resting behavior of Anopheles mosquitoes. There were no clear patterns for African malaria vectors, and standardized methods for monitoring resting behavior are necessary before a spray campaign is implemented. The existing data on selective spraying indicate that this may be a promising way of controlling malaria, but further work is necessary. The overall impact of selective IRS on control program costs could be substantial, reducing the total program costs by up to 30-40%, which could help mitigate some of the increased program costs incurred over the past few years and help maintain IRS coverage and impact. However, these cost reductions must also be carefully considered against the total cost of an IRS program, not just the spraying operations and insecticide costs. IRS is being phased out from an increasing number of countries due to its cost despite clear evidence of effectiveness for malaria control and insecticide resistance management. Several operational studies have indicated substantial decreases in malaria prevalence using selective spraying at a fraction of the cost of full spraying. Studies that evaluate the entomological and epidemiological impact of selective spraying with existing IRS compounds are urgently required to enable this method to be fully validated and, if successful, pass on these cost savings to help maintain this important vector control tool. Abbreviations DDT: Dichlorodiphenyltrichloroethane IRS: Indoor residual spraying ITN: Insecticide-treated Net PAHO: Pan American Health Organization WHO: World Health Organization PMI: Presidents Malaria Initiative Declarations Ethics approval and consent to participate Not applicable Consent for publication Not applicable Availability of data and materials There is no new data presented here, and all can be found in published articles. Excel files for the cost model are available upon request. Competing interests The authors declare that they have no competing interests. Funding This publication is based on research funded by IVCC, which receives the generous support of the American people through the United States Agency for International Development (USAID), the Bill & Melinda Gates Foundation, the Swiss Agency for Development and Cooperation (SDC) and UK International Development funds from the UK government. The contents, findings and conclusions contained within are those of the authors and do not necessarily reflect positions or policies of USAID, the Bill & Melinda Gates Foundation, the United States Government, the UK Government, nor SDC. Authors’ contributions Conceptualization: SRI, SJM. Methodology: SRI, SJM, DN (cost model). Literature review: SRI. Analysis: SRI. Writing – original draft: SRI. Development of cost model and writing: DN. Writing – review and editing: SRI, DN, JB, FT, PM, SJM. All authors read and reviewed the final version. Acknowledgements Natalie Lissenden (IVCC) is kindly thanked for her review of the manuscript. Authors’ information References Aghajanyan A, Riley M, Tesso E, Won N, Dawadi S, Longman B. April 2023. PMI IRS Country Programs: 2022 Comparative Cost Analysis. Rockville, MD. PMI VectorLink Project, Abt Associates Inc. Asinas CY, Hugo CT, Boase CJ, Evans RG. Evaluation of selective spraying of bendiocarb (Ficam VC ® ) for the control of Anopheles flavirostris in the Philippines. J Am Mosquito Contr Assoc. 1994; 10:496-500. Arredondo-Jiménez JI, Bown DN, Rodríguez MH, Loyola EG. Control of Anopheles albimanus mosquitos in southern Mexico by spraying their preferred indoor resting sites. B World Health Organ. 1995; 73: 329-337. Bath D, Cook J, Govere J, Mathebula P, Morris N, Hlongwana K et al. Effectiveness and cost-effectiveness of reactive, targeted indoor residual spraying for malaria control in low-transmission settings: a cluster-randomised, non-inferiority trial in South Africa. Lancet. 2021; 397: 816-827. Bown DN, Rios JR, del Angel Cabañas G, Guerrero JC, Méndez JF. Evaluation of chlorphoxim used against Anopheles albimanus on the south coast of Mexico: 1. Results of indoor chlorphoxim applications and assessment of the methodology employed. Bull Pan Am Health Organ. 1984; 18: 379-388. Chabi J, Seyoum A, Edi C, Kouassi BL, Yihdego Y, Oxborough R, et al. Efficacy of partial spraying of SumiShield, Fludora Fusion and Actellic against wild populations of Anopheles gambiae s.l. in experimental huts in Tiassale, Côte d’Ivoire. Sci Rep. 2023; 13:11364 Chow CY, Liang KC, Pletsch DJ. Observations on anopheline populations in human dwellings in southern Taiwan (Formosa). Indian J Malariol. 1951; 5: 569-577. Coleman S, Yihdego Y, Sherrard-Smith E, Churcher TS, Dengela D, Oxborough RM, et al. Partial indoor residual spraying with pirimiphos-methyl as an effective and cost-saving measure for the control of Anopheles gambiae s.l. in northern Ghana. Sci Rep. 2021; 11:18055. Damar T, Fleming GA, Gandahusada S, Bang YH. Nocturnal indoor resting heights of the malaria vector Anopheles aconitus and other anophelines (Diptera: Culicidae) in Central Java, Indonesia. J Med Entomol. 1981; 18: 362-365. Deane LM, Damasceno RG. Altura de pouso das fêmeas de Anopheles darlingi e de Anopheles aquasalis nas paredes internas das casas. Mem Inst Evandro Chagas : Parasitologia. 1948; 2: 317-323. Dunbar MW, Correa-Morales F, Dzul-Manzanilla F, Medina-Barreiro A, Bibiano-Marín W, Morales-Ríos E, et al. Efficacy of novel indoor residual spraying method targeting pyrethroid-resistant Aedes aegypti within experimental houses. PLoS Negl Trop Dis. 2019; 13:e0007203. Elliott R. The influence of vector behavior on malaria transmission. Am J Trop Med Hyg. 1972; 21: 755-763. Logan JA. The Sardinian Project: An experiment in the eradication of an indigenous malarious vector. 1953. The Johns Hopkins Press: Baltimore. Gandahusada S, Fleming GA, Sukamto, Damar T, Suwarto, Sustriayu N, et al. Malaria control with residual fenitrothion in Central Java, Indonesia: an operational-scale trial using both full and selective coverage treatments. B World Health Organ. 1984; 62:783-794. Gramiccia G, Garrett-Jones C, El Din Sultan G. Band spraying. An experiment on cheaper residual spraying in malaria control. 1953; J Med Libanais, 245–256 Johns, Benjamin and Altea Cico Sitruk. May 2019. PMI IRS Country Programs: 2018 Comparative Cost Analysis. Rockville, MD. PMI VectorLink Project, Abt Associates Inc. Johns, Benjamin and Haile, Mignote. May 2021. PMI IRS Country Programs: 2020 Comparative Cost Analysis. Rockville, MD. PMI VectorLink Project, Abt Associates Inc. Kirstein OD, Culquichicon C, Che-Mendoza, Navarrete-Carballo J, Wang J, Bibiano-Marin W, et al. Targeted indoor residual insecticide applications shift Aedes aegypti age structure and arbovirus transmission potential. Sci Rep. 2023; 13:21271. Lassen K, Liu SY, Lizarzaburu C, Ríos R. Preliminary report on the effect of selective application of propoxur on indoor surfaces in El Salvador. American Journal of Tropical Medicine and Hygiene. 1972; 21:813-818. Lines JD, Lyimo EO, Curtis CF. Mixing of indoor-and outdoor-resting adults of Anopheles gambiae Giles s.l. and A. funestus Giles (Diptera: Culicidae) in coastal Tanzania. Bulletin of Entomological Research 1986; 76: 171-178. Mathis W, St. Cloud A, Eyraud M, Miller S, Hamon J. Initial field studies in Upper Volta with dichlorvos residual fumigant as a malaria eradication technique. 2. Entomological Evaluation. Bull World Health Organ. 1963; 29: 237-241. Manrique-Saide P, Dean NE, Halloran ME, Longini IM, Collins MH, Waller LA, et al. The TIRS trial: protocol for a cluster randomized controlled trial assessing the efficacy of preventive targeted indoor residual spraying to reduce Aedes-borne viral illnesses in Merida, Mexico. Trials. 2021; 21, 839. Monroe A, Moore S, Olapeju B, Merritt AP, Okumu F. Unlocking the human factor to increase effectiveness and sustainability of malaria vector control. Malaria J. 2021 ; 20: 404. Mosha JF, Matowo NS, Kulkarni MA, Messenger LA, Lukole E, Mallya E, et al. Effectiveness of long-lasting insecticidal nets with pyriproxyfen-pyrethroid, chlorfenapyr-pyrethroid, or piperonyl butoxide-pyrethroid versus pyrethroid only against malaria in Tanzania: final-year results of a four-arm, single-blind, cluster-randomised trial. Lancet Infect Dis. 2023; S1473-3099(23)00437-1. Msugupakulya BJ, Kaindoa EW, Ngowo HS, Kahamba NF, Msaky DS, Matoke-Muhia D, et al. Preferred resting surfaces of dominant malaria vectors inside different house types in rural south-eastern Tanzania. Malar J. 2020; 19: 22. Mutinga MJ, Odhiambo TR, Kamau CC, Odulaja A, Amimo FA, Wachira DW. Choice of resting sites by Anopheles gambiae (Diptera: Culici) in Mwea Rice Irrigation Scheme, Kirinyaga District, Kenya. East Afr Med J. 1995; 72: 170-175. Osae MY. 2014. Resting behaviour of endophilic anopheline vectors in three ecological zones of southern Ghana and its implications for the use of entomopathogenic fungi. PhD thesis. University of Ghana. Oxborough RM. Trends in US President’s Malaria Initiative-funded indoor residual spray coverage and insecticide choice in sub-Saharan Africa (2008-2015): urgent need for affordable, long-lasting insecticides. Malar J. 2016; 15:146. Pan American Health Organization. 2019. Manual for indoor residual spraying in urban areas for Aedes aegypti control. Washington DC. 60pp. Pletsch DJ, Demos EA. Selective spraying of premises in the control of minimus-transmitted malaria in Taiwan. 1954; World Health Organization: WHO/MAL/107. Protopopoff N, Mosha JF, Lukole E, Charlwood JD, Wright A, Mwalimu CD, et al. Effectiveness of a long-lasting piperonyl butoxide-treated insecticidal net and indoor residual spray interventions, separately and together, against malaria transmitted by pyrethroid-resistant mosquitoes: a cluster, randomized controlled, two-by-two factorial design trial. Lancet. 2018; 391: 1577-1588. Quiñones ML, Suarez MF. Indoor resting heights of some anophelines in Colombia. J Am Mosquito Contr Assoc. 1990; 6:602-604. Rehman AM, Coleman M, Schwabe C, Baltazar G, Matias A, Gomes IR, et al. How much does malaria control quality matter: the epidemiological impact of holed nets and inadequate indoor residual spraying. 2011; PLoS One 6: e19205. Russell PF, West LS, Manwell RD, MacDonald G. 1963. Practical malariology. 2 nd edition. Oxford University Press, London xiv+750p. Sahu SS, Gunasekaran P, Vanamail P, Jambulingam P. Seasonal prevalence & resting behaviour of Anopheles minimus Theobald & An. fluviatilis James (Diptera: Culicidae) in east-central India. Indian J Med Res. 2011; 133: 655-661. Sande S, Zimbe M, Chinwada P, Masendu HT, Makuwaza A. Insights into resting behavior of malaria vector mosquitoes in Mutare and Mutasa districts of Manicaland Province, Zimbabwe. Journal of Medical Entomology. 2016; 53:866-872. Smith A. The distribution and host choice of resting A. gambiae Giles and A. funestus Giles in cone huts on Ukara Island, Tanganyika. East Afr Med J. 1955; 32: 7-13. Smith A. Studies on domestic habits of A. gambiae that affect its vulnerability to insecticides. Part I. Resting places in huts. East Afr Med J 1962; 39: 15-24. Urbino CM, Digma F, Abinoja B. 1961. Behavior pattern of adults of Anopheles minimus flavirostris Ludlow. Philippine J Sci. 1961; 371-376. Vazquez-Prokopec GM, Che-Mendoza A, Kirstein OD, Bibiano-Marin W, González-Olvera G, Medina-Barreiro A, et al. Preventive residual insecticide applications successfully controlled Aedes aegypti in Yucatan, Mexico. Sci Rep. 2022; 12:21998. Verhulst NO, Brendle A, Blanckenhorn WU, Mathis A. Thermal preferences of subtropical Aedes aegypti and temperate Ae. japonicus mosquitoes. J Therm Bio. 2020; 91: 102637. WHO. Global Plan for Insecticide Resistance Management in Malaria Vectors. 2012. WHO/HTM/GMP/2012.5 WHO. Operational manual on indoor residual spraying. Control of vectors of malaria, Aedes-borne diseases, Chagas disease, leishmaniases and lymphatic filariasis. 2023. Geneva, World Health Organization WHO. World malaria report 2023. Geneva: World Health Organization. 2023; License: CC BY-NC-SA 3.0 IGO. WHO. WHO Guidelines for malaria. WHO/UCN/GMP/2023.01 Rev1. 2023; Geneva: World Health Organization. Yukich J, Digre P, Scates S, Boydens L, Obi E, Moran N, et al. Incremental cost and cost-effectiveness of the addition of indoor residual spraying with pirimiphos-methyl in sub-Saharan Africa versus standard malaria control: results of data collection and analysis in the Next Generation Indoor Residual Sprays (NgenIRS) project, an economic-evaluation. 2022; Malar J; 21(1): 185. Tables Table 1: Studies evaluating the resting sites of major African malaria vectors in houses Reference Country Species Type of house Percentage on walls Percentage on roofs Percentage on other Osae 2014 Ghana An. gambiae Mud, brick, and cement houses with tile or metal roofs 9 56 35 Sande et al. 2016 Zimbabwe Mud, brick, and cement houses with tile or metal roofs 36 42 16 Coleman et al. 2021 Ghana Experimental hut, tarpaulin ceiling 51 45 5 MEAN 32 48 19 Osae 2014 Ghana An. coluzzii Mud, brick, and cement houses with tile or metal roofs 29 25 45 Chabi et al. 2023 Côte d'Ivoire Experimental hut, plywood ceiling 63 31 6 MEAN 46 28 26 Osae 2014 Ghana An. funestus Mud, brick, and cement houses with tile or metal roofs 23 59 18 Sande et al. 2016 Zimbabwe Mud, brick, and cement houses with tile or metal roofs 40 50 7 Msugupakulya et al. 2020 Tanzania Thatched roofs and mud walls, no ceiliings 18 55 27 Msugupakulya et al. 2020 Tanzania Thatched roofs and brick walls, no ceilings 25 33 43 Msugupakulya et al. 2020 Tanzania Metal roofs and unplastered brick walls, no ceilings 37 16 47 Msugupakulya et al. 2020 Tanzania Metal roofs and plastered brick walls, no ceilings 27 20 53 MEAN 28 39 32 Msugupakulya et al. 2020 Tanzania An. arabiensis Thatched roofs and mud walls 21 43 36 Msugupakulya et al. 2020 Tanzania Thatched roofs and brick walls 13 50 38 Msugupakulya et al. 2020 Tanzania Metal roofs and unplastered brick walls 27 8 66 Msugupakulya et al. 2020 Tanzania Metal roofs and plastered brick walls 10 30 60 MEAN 18 33 50 Table 2: The impact and cost savings of selective spraying studies Study Location Main vector(s) Insecticide Type of selective spraying Impact of selective spraying compared with full spraying Reported cost savings with selective spraying (%) Reduction in insecticide use (%) Based on the reduction in days required to spray an equivalent number of houses Overall reduction in total operational costs (cost model) (%) Reduction in spray team wages/meals (%) Reduction in transport costs (%) Gramiccia et al. 1953 Lebanon An. sacharovi, An. superpictus DDT Horizontal band spraying Difficult to determine, substantial decrease in all arms (including control) 31.3 35.8 26.3 21.7 15.4 Pletch & Demos 1954 Taiwan An. minimus DDT Focusing spraying on sleeping rooms After two rounds of spray, infant parasite rates were 0% in both arms 25.6 38.4 - - - Lassen et al. 1972 El Salvador An. albimanus Propoxur Two swaths on the inner side of the roof and in the angle between the roof and the wall Full spraying not evaluated, but ~10% of malaria prevalence in selective spray area compared to control area 50-60 - - - - Gandahusada et al. 1984 Indonesia An. aconitus fenitrothion Sprayed between 10 and 85cm Substantial decrease in both arms, but more impact on P. falciparum with full spraying. 68.0 64.5 46.0 46.0* 28.6 Asinas et al. 1994 Philippines An. flavirostris bendiocarb Experimental huts sprayed up to 0.7m on the walls, and all areas within 0.1m of the door, window, and internal and external eaves. Never more than 8% difference in mosquito mortality compared to the fully sprayed hut 36% spray time, 49% less insecticide 49.0 36.0 36.0* 21.9 Arredondo-Jimenez et al. 1995 Mexico An. albimaus bendiocarb Experimental huts sprayed with two 1m horizontal swaths, one from 0.75-1.75cm on the walls, and one on the roof, starting at its intersection with the wall. No significant difference in mortality between fully sprayed and selective sprayed huts. 40.0 40.5 † 38.5 † 38.5* 19.5 Dunbar et al. 2019 Mexico Ae. aegypti bendiocarb Experimental houses sprayed on walls below 1.5m and under furniture (targeted IRS, TIRS) or under furniture only (resting site targeted IRS, RS-TIRS) No difference in first two months for RS-TIRS, or for first 4 months with TIRS TIRS 38.0 31.0 31.0* 17.5 RS-IRS 85.0 82.0 82.0* 41.1 Coleman et al. 2021 Ghana An. gambiae s.l. pirimiphos-methyl Experimental huts sprayed with bottom half, bottom half+ceiling, top half, top half+ceiling, or full spray. A field study that compared full spraying, selective spraying (top half+ceiling), and no spray. No significant differences in mortality or human biting rates between fully and selectively sprayed huts/houses. Both were better than control. 36.0 39.2 25.7 25.7 17.0 * extrapolated from percentage saving in spray team wages/time † extrapolated from table 3 in the publication Additional Declarations No competing interests reported. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4230947","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Systematic Review","associatedPublications":[],"authors":[{"id":301882297,"identity":"dcdc02b0-b813-4160-a4c2-927e9a31a9f3","order_by":0,"name":"Seth Irish","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA2ElEQVRIiWNgGAWjYHACNoYEBgkGA/YGINvAghgdzFAtPAdAWiSI1MIAVpwAoojQIt/ef+zBwz0W9uaSz69u+FEgwcDf3p2AV4vBmcPsBgnPJBJ3zs4pu9kDdJjEmbMb8GuRSGaTSDggkWBwOyftBg9Qi4FELn4t8vMfg7XYG9w8k3bzDzFaGG4wg7UwbrjBfuw2UbYYnEk2A2lJ3HAmh+22jIEED0G/yLcffCb540CdvcHx489uvvljI8ff3kvAYQjAYwAmiVUOAuwPSFE9CkbBKBgFIwgAAIa8Riozx1HMAAAAAElFTkSuQmCC","orcid":"","institution":"Swiss Tropical and Public Health Institute","correspondingAuthor":true,"prefix":"","firstName":"Seth","middleName":"","lastName":"Irish","suffix":""},{"id":301882298,"identity":"620b1c7e-9c99-469e-9619-61703b64ee34","order_by":1,"name":"Derric Nimmo","email":"","orcid":"","institution":"IVCC, Liverpool School of Tropical Medicine","correspondingAuthor":false,"prefix":"","firstName":"Derric","middleName":"","lastName":"Nimmo","suffix":""},{"id":301882299,"identity":"3c4ed21d-82e3-478a-911f-db1eb1ed2205","order_by":2,"name":"Jameel Bharmel","email":"","orcid":"","institution":"IVCC, Liverpool School of Tropical Medicine","correspondingAuthor":false,"prefix":"","firstName":"Jameel","middleName":"","lastName":"Bharmel","suffix":""},{"id":301882300,"identity":"4aa9c4ac-acfc-4972-88bc-df8e1d9ead6b","order_by":3,"name":"Frederic Tripet","email":"","orcid":"","institution":"Swiss Tropical and Public Health Institute","correspondingAuthor":false,"prefix":"","firstName":"Frederic","middleName":"","lastName":"Tripet","suffix":""},{"id":301882301,"identity":"185de610-369f-4365-8060-d276c092cef3","order_by":4,"name":"Pie Müller","email":"","orcid":"","institution":"Swiss Tropical and Public Health Institute","correspondingAuthor":false,"prefix":"","firstName":"Pie","middleName":"","lastName":"Müller","suffix":""},{"id":301882302,"identity":"77ac41d1-5f2c-44ad-b1cb-fddad403379d","order_by":5,"name":"Pablo Manrique-Saide","email":"","orcid":"","institution":"Unidad Colaborativa para Bioensayos Entomológicos, Universidad Autónoma de Yucatán","correspondingAuthor":false,"prefix":"","firstName":"Pablo","middleName":"","lastName":"Manrique-Saide","suffix":""},{"id":301882303,"identity":"f6432a74-168d-422d-999e-6d0f88daac88","order_by":6,"name":"Sarah J. Moore","email":"","orcid":"","institution":"Swiss Tropical and Public Health Institute","correspondingAuthor":false,"prefix":"","firstName":"Sarah","middleName":"J.","lastName":"Moore","suffix":""}],"badges":[],"createdAt":"2024-04-07 10:44:23","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4230947/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4230947/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1186/s12936-024-05053-3","type":"published","date":"2024-08-23T15:57:06+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":57206105,"identity":"31256814-bfcd-47df-b1e7-3b514e3b25fc","added_by":"auto","created_at":"2024-05-27 11:09:55","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":335805,"visible":true,"origin":"","legend":"\u003cp\u003ePercentage breakdown of the average PMI VectorLink IRS spray campaign program costs (2018-2021).\u003c/p\u003e","description":"","filename":"Figure1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4230947/v1/1c5f4851f124d91e9bb8d792.jpg"},{"id":57206106,"identity":"8101357f-5b07-47ab-9bfc-23058ed7e92e","added_by":"auto","created_at":"2024-05-27 11:09:55","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":443052,"visible":true,"origin":"","legend":"\u003cp\u003eAn example of the cost model inputs and outputs.\u003c/p\u003e","description":"","filename":"Figure2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4230947/v1/46cf9ccbe994b1fdccefbbc2.jpg"},{"id":63300055,"identity":"34ca0458-2420-419f-a188-c6d8c5337838","added_by":"auto","created_at":"2024-08-26 16:10:41","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1467564,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4230947/v1/9b6739ed-9b2b-4dbe-b80c-e79001610f2b.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"A review of selective indoor residual spraying for malaria control","fulltext":[{"header":"Introduction","content":"\u003cp\u003eMalaria continues to cause high levels of morbidity and mortality, particularly in Africa, where the majority of malaria cases occur (WHO 2023). In 2022, malaria cases increased to an estimated 249 million cases, resulting in an estimated 608,000 deaths (WHO 2023). To decrease the number of cases, it is important to invest in effective testing and treatment of malaria, as well as undertaking strategies that prevent malaria transmission. Vector control is the most effective current malaria prevention strategy, and the main techniques employed are the distribution of insecticide-treated nets (ITNs) and indoor residual spraying (IRS). In recent years, there has been the development of highly effective nets with different active ingredients (e.g. Mosha et al. 2023; Protopopoff et al. 2018). This has resulted in some countries stopping their IRS programs, partly due to cost considerations, even though IRS remains highly cost effective (Oxborough 2016; Yukich et al. 2022). However, IRS has several advantages which might be useful if the costs of IRS could be reduced. These advantages include the possibility for insecticide rotation as part of a resistance management plan (WHO 2012), less necessity for active utilization (as compared to ITNs, which must be put in place by homeowners each night) (Monroe et al. 2021), and, similar to ITNs, IRS can have a community protection effect when coverage is high (Rehman et al. 2011).\u003c/p\u003e\n\u003cp\u003eOne way to decrease the cost of IRS is through selective indoor spraying of some of the surfaces in houses. It should be noted that selective spraying is sometimes termed \u0026ldquo;targeted IRS\u0026rdquo; (Manrique-Saide et al. 2020) or \u0026ldquo;partial IRS\u0026rdquo; (Coleman et al. 2021) that should be distinguished from the targeted application of IRS to areas where there is evidence of recent malaria transmission rather than blanket application to all houses (Bath et al. 2021). Conventional IRS recommended by WHO for malaria control (WHO 2023) involves the full spraying of all indoor walls and often the ceilings of houses. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOptimally, the selective indoor spray is applied where mosquitoes are most likely to rest (WHO 2023). Selectively applying residual insecticides, e.g., for \u003cem\u003eAedes aegypti\u003c/em\u003e on exposed lower sections of walls (\u0026lt; 1.5 m), under furniture, and on dark surfaces throughout houses provides an entomological impact similar to spraying entire walls (as performed in classic IRS), but in a fraction of the time (\u0026lt; 18%) and insecticide volume (\u0026lt; 30%) compared to classic IRS (Manrique-Saide et al. 2020). Other studies have shown important impacts using selective spraying (Vazquez-Prokopec et al. 2022; Karstein et al. 2023). This selective spraying approach is endorsed by the Pan American Health Organization for IRS spraying for control of \u003cem\u003eAedes aegypti\u003c/em\u003e in urban settings (PAHO 2019). While numerous studies have been done to evaluate selective IRS for malaria control, this work has not provided conclusive findings required to change current policies. This narrative review summarizes previous research on the use of selective spraying for vector-borne disease control and the cost-saving implications to see whether there might be justification for the use of selective spraying for malaria control, and to determine what avenues of research might be the most impactful to maximize its efficacy.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cp\u003e\u003cem\u003eSelection criteria\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eStudies were included if they considered the two key questions of this review: resting behavior of \u003cem\u003eAnopheles\u003c/em\u003e mosquitoes or efficacy of selective indoor residual spraying. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eSearch strategy\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eAn initial search was conducted on PubMed in July 2022,\u0026nbsp;without language or date limits to find 1) studies that assessed the resting behaviour of \u003cem\u003eAnopheles\u003c/em\u003e mosquitoes and 2) studies that evaluated the impact of selective spraying on entomological and malaria outcomes. Search terms included\u0026nbsp;“partial indoor residual spraying” and “targeted indoor residual spraying”.\u0026nbsp;Additional articles were identified through hand searches of all references cited in articles identified through the initial search.\u0026nbsp;This process continued until no further related articles were found.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eData extraction\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eData from the selected papers were extracted to determine the resting heights and behaviors of \u003cem\u003eAnopheles\u003c/em\u003e mosquitoes. Additionally, data was extracted from articles that discussed the impact of selective spraying, and the impact and cost savings of these studies were summarized.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eCost analysis\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eA cost model was constructed from the PMI VectorLink IRS country programs comparative cost analysis reports. The model is based mainly on the 2018 data across the 14 countries where PMI VectorLink performed IRS (Johns et al. 2019). A comparison to the cost analysis data from 2019-2022 shows that the relative cost breakdown for each area has not changed significantly (data not shown). The spray campaign costs were broken down further using the following data and assumptions. Training costs were calculated from the average percentage spray campaign costs used for Malawi, Rwanda and Uganda for training of trainers and SOP and team leader training (data provided by PMI VectorLink). Spray campaign personnel costs were calculated from the total campaign days and the daily wages minus the training costs. The rest of the spray campaign costs were assigned to transportation of spray personnel (mainly vehicle hire, drivers and fuel).\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eThe main results from this review were separated into two categories, 1) description of the resting sites of mosquitoes inside houses and 2) reports of experiments or operational pilots of selective spraying. Seventeen studies were found reporting the resting sites of mosquitoes in houses, and nine were found reporting on experiments or pilot studies of selective spraying.\u003c/p\u003e\n\u003ch2\u003eResting sites of mosquitoes in houses\u003c/h2\u003e\n\u003cp\u003e\u003cem\u003eResting height\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe results collated from the reviewed publications showed clear evidence that the resting sites and behavior of the mosquitoes vary. These variations were observed both between and occasionally within species. In many of the publications, the height (distance above the floor) at which mosquitoes were collected was reported.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBased on these data, it was determined that \u003cem\u003eAnopheles darlingi\u003c/em\u003e, \u003cem\u003eAnopheles aquasalis, Anopheles ludlowi, Anopheles hyrcanus, Anopheles fluviatilis, Anopheles leucosphyrus, Anopheles aconitus, Anopheles kochi, Anopheles subpictus, Anopheles indefinitus, Anopheles marajoara\u003c/em\u003e, \u003cem\u003eAnopheles punctimacula, Anopheles nuneztovari\u003c/em\u003e, and \u003cem\u003eAnopheles flavirostris\u003c/em\u003e tended to rest primarily on the lower half of walls (Deane \u0026amp; Damasceno 1948, Chow et al. 1951, Russell 1963, Elliott 1972, Damar et al. 1981, Quiñones \u0026amp; Suarez 1990, Asinas et al. 1994).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn contrast, \u003cem\u003eAnopheles barbirostris\u003c/em\u003e, \u003cem\u003eAnopheles oswaldi\u003c/em\u003e, and \u003cem\u003eAnopheles rangeli\u003c/em\u003e were found to rest above 1.5m above the floor, and often higher (Damar et al. 1981, Quiñones \u0026amp; Suarez 1990). Sahu et al. (2011) found 99% of \u003cem\u003eAnopheles minimus\u003c/em\u003e and \u003cem\u003eAnopheles fluviatilis\u003c/em\u003e to rest on walls (as opposed to eaves, hanging objects, and the roof), with most of these mosquitoes resting between 90-125 cm from the ground.\u003c/p\u003e\n\u003cp\u003eIt is important to note that most of these studies were conducted outside of Africa. Despite this, a few key studies based in Africa have investigated the resting behavior of \u003cem\u003eAnopheles gambiae\u003c/em\u003e \u003cem\u003es.l.\u003c/em\u003e and\u003cem\u003e\u0026nbsp;Anopheles funestus\u0026nbsp;\u003c/em\u003evectors\u003cem\u003e.\u0026nbsp;\u003c/em\u003eThese studies can largely be grouped into monitoring the height of the resting site on the wall or roof, additional observations about the substrate on which mosquitoes rest, and their resting behaviour conducted within experimental huts were also noted.\u003c/p\u003e\n\u003cp\u003eIn his first study looking at the resting height of malarial vectors, Smith (1955) investigated the distribution of \u003cem\u003eAn. gambiae\u003c/em\u003e and \u003cem\u003eAn. funestus\u003c/em\u003e vectors in cone huts on Ukara Island (a Tanzanian island in Lake Victoria, near Mwanza). These cone huts measured 6.4m high and 6.9m wide at their bases, and typically housed both humans and cattle. The huts were searched until all observable mosquitoes had been collected and their location of collection was recorded. From the trial it was shown that the vast majority of female mosquitoes (80% of \u003cem\u003eAn. gambiae\u003c/em\u003e and 79% of \u003cem\u003eAn. funestus\u003c/em\u003e) were found to be resting below 2.1m (from the floor) in the huts during the rainy season. The majority of these rested on the human-habited side of the huts; nevertheless, considerable numbers were also found on the cattle-habited side of the huts. The same trend was found during the dry season. Later, Smith (1962) collected mosquitoes from houses of three different types (\u003cem\u003etembe\u003c/em\u003e, \u003cem\u003emsonge\u003c/em\u003e, and \u003cem\u003ebanda\u003c/em\u003e) in Tanzania. Initial catches were conducted between 0800-1200 with additional complementary catches between 1100-1500 being conducted three days later. During the collection period, the proportion of \u003cem\u003eAn. gambiae\u003c/em\u003e mosquitoes resting on the roof ranged from 42% to 74%. There were no large differences between the proportions resting on the roof during the night and day, but there were differences in roof-resting between the different types of huts. Mathis et al. (1963) reported 94.6% of \u003cem\u003eAn. gambiae\u003c/em\u003e and \u003cem\u003eAn. funestus\u003c/em\u003e were collected on the ceilings in monitored huts. On the contrary, Mutinga et al. (1995) noted \u003cem\u003eAn. gambiae\u0026nbsp;\u003c/em\u003emosquitoesresting primarily on the lower parts of walls and the darker parts of the room. Osae (2014) found large proportions of all three species resting above 2m (\u003cem\u003eAn. gambiae\u003c/em\u003e: 76%, \u003cem\u003eAnopheles coluzzii\u003c/em\u003e 58%, \u003cem\u003eAn. funestus\u003c/em\u003e 74%), and preferably on dark materials in cool, humid areas. Sande et al. (2016) found the highest proportion of \u003cem\u003eAn. funestus\u003c/em\u003e and \u003cem\u003eAn. gambiae\u003c/em\u003e on the roof (although considerable numbers were found on walls, with fewer mosquitoes collected on furniture. When only wall surfaces were considered, the majority were collected below 1 meter (44% of \u003cem\u003eAn. funestus\u003c/em\u003e, 64% of \u003cem\u003eAn. gambiae\u003c/em\u003e\u003cem\u003e\u0026nbsp;s.l.\u003c/em\u003e). Msugupakulya et al. (2020) evaluated the resting sites of \u003cem\u003eAn. gambiae\u003c/em\u003e and \u003cem\u003eAn. funestus\u003c/em\u003e in different types of houses. They found that the highest numbers of mosquitoes rested on the roof in houses with thatched roofs (with the exception of \u003cem\u003eAn. funestus\u003c/em\u003e in brick houses), and in houses with metal roofs, the highest numbers of mosquitoes rested on surfaces other than walls or roofs. It is worth noting that in all types of houses, mosquitoes were found resting on walls, roofs, and other surfaces (Table 1).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eResting substrate\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eOther studies have looked at the effect of resting substrate or other factors on the resting behavior of African malaria vectors. Smith (1962) evaluated the impact of different factors within experimental huts to evaluate their impact on mosquito resting behavior. He found that neither building a partition wall in the hut, modifying the hut entry site, adding a ceiling, modifying the surface of the roof, nor the abdominal status (or source of blood meal) appeared to change the resting behavior of \u003cem\u003eAn. gambiae\u0026nbsp;\u003c/em\u003ein terms of resting on the roof or walls. However, modifying the substrate of the walls (from smooth mud to rough mud) resulted in greater resting on rough mud walls. Similarly, making a fire inside the huts resulted in decreased resting on the roof and increased resting on walls. Beds were not a major resting site for mosquitoes in experimental huts, with only nine percent of mosquitoes collected from beds. Mutinga et al. (1995) found that \u003cem\u003eAn. gambiae\u003c/em\u003e preferred to rest on fabric attached to the walls. Osae found differences in resting sites between \u003cem\u003eAn. gambiae\u003c/em\u003e, \u003cem\u003eAn. coluzzii\u003c/em\u003e, and \u003cem\u003eAn. funestus\u003c/em\u003e in Ghana (2014). He found the main resting sites to be roofing beams for \u003cem\u003eAn. gambiae\u003c/em\u003e (28%), on netting or frames of windows for \u003cem\u003eAn. coluzzii\u0026nbsp;\u003c/em\u003e(20%), and for \u003cem\u003eAn. funestus,\u003c/em\u003e it was the roof. He also looked at the materials that mosquitoes were resting, with \u003cem\u003eAn. gambiae\u003c/em\u003e and \u003cem\u003eAn. funestus\u003c/em\u003e resting primarily on wood surfaces, and \u003cem\u003eAn. coluzzii\u003c/em\u003e resting on nylon. \u0026nbsp;\u003c/p\u003e\n\u003ch2\u003eResting sites of mosquitoes in experimental huts\u003c/h2\u003e\n\u003cp\u003eFinally, some studies taking place in experimental huts have monitored the resting behavior prior to introducing interventions such as wall spraying. Smith (1962) found higher proportions of \u003cem\u003eAn. gambiae\u0026nbsp;\u003c/em\u003eresting on the roof in experimental huts than in other types of structures, with 94-97% of mosquitoes resting on roofs, compared with 42-74% in local houses. Coleman et al. (2021) monitored the resting sites of \u003cem\u003eAn. gambiae\u003c/em\u003e\u003cem\u003e\u0026nbsp;s.l.\u0026nbsp;\u003c/em\u003ecollected in West African experimental huts in Ghana. The majority of \u003cem\u003eAn. gambiae\u003c/em\u003e \u003cem\u003es.l.\u0026nbsp;\u003c/em\u003ewere collected from the ceiling and the top half of the veranda. In a follow up study, Chabi et al. (2023) found 43% of \u003cem\u003eAn. gambiae\u003c/em\u003e \u003cem\u003es.l.\u0026nbsp;\u003c/em\u003eresting on the lower half of walls, 24% of mosquitoes resting on the top half of walls, and 33% of mosquitoes resting on ceiling. \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003ch2\u003eEvaluation of selective spraying\u003c/h2\u003e\n\u003cp\u003eIn the first year of the “Sardinian Project” an attempt to eliminate \u003cem\u003eAnopheles labranchiae\u003c/em\u003e from Sardinia, selective spraying was conducted with spraying of walls below 1.5m in the first campaign (1946-1947), but in successive campaigns “full spraying” was conducted (Logan 1953). Malaria cases declined from 74,641 in the first year (1946) to 39,303 in the second (Tognotti 2009), although the impact of selective spraying with DDT cannot be disentangled from the impact of large-scale aerial adulticide/larvicide application and source reduction that was carried out in parallel. This highlights the previous/historical use of selective IRS, however, no further details on impact of the intervention were provided in this source.\u003c/p\u003e\n\u003cp\u003eAnother method of selective spraying was evaluated in Lebanon (Gramiccia 1953), where “band spraying” was attempted, spraying horizontal swaths of DDT of 30cm width separated by an equal distance of unsprayed areas (all 1m above the ground). The impact of this type of spraying was measured in areas where \u003cem\u003eAnopheles sacharovi\u003c/em\u003e and \u003cem\u003eAnopheles superpictus\u003c/em\u003e were the main vectors both by looking at malaria rates, and collection of \u003cem\u003eAnopheles\u003c/em\u003e in houses in areas where full spraying or selective spraying had been conducted (relative to control areas). While no impact on parasite rates was found, due to a drop in cases in both control and treatment areas, there was a reduction in \u003cem\u003eAnopheles\u003c/em\u003e in the full and selectively sprayed houses. The authors estimated the cost savings that might be found with selective spraying was approximately 31.3% (including the costs of DDT, labor, transport, storage, etc.) (Table 2).\u003c/p\u003e\n\u003cp\u003ePletsch and Demos (1954) reported “selective spraying” in Taiwan against \u003cem\u003eAnopheles minimus\u003c/em\u003e. Full spraying was conducted by spraying walls, roofs, ceilings, and undersides of furniture with DDT (2g/m\u003csup\u003e2\u003c/sup\u003e). The inner walls and undersides of roofs of all outbuildings were also sprayed except for the first 50cm of the wall in pig pens. “Selective spraying” was done in several ways; on the walls of bedrooms and storerooms, the underside of the roof in bedrooms, the ceilings in bedrooms and storerooms (which were quite rare), the undersides of furniture and window recesses in bedrooms, storerooms, sitting rooms, and kitchens (only inside and under the food cabinet), and the underside of the bed or bed platform in bedrooms. Any room in which people slept was considered a bedroom. The results from two rounds of both spray types were positive, reducing malaria rates from over 20% to less than 1% in Chi-Shan, and reducing them from about 2% to 0% in an additional study in central Taiwan. Both entomological investigations supported the finding of effective control and reduction of the numbers of mosquitoes collected in bedrooms to zero with both techniques. The cost savings were generated from spraying 38.4% less surface area in the selective spraying treatment, and the overall costs were reduced by 25.6%. However, some disadvantages of selective spraying were noted, specifically, the detection of \u003cem\u003eAn. minimus\u003c/em\u003e mosquitoes in cattle sheds (a possible harborage that could result in the build-up of resistance), the detection of \u003cem\u003eAnopheles sinensis\u003c/em\u003e in cattle sheds that bothered the farmers’ water buffalo, and hesitation from homeowners and sprayers about receiving less than full coverage.\u003c/p\u003e\n\u003cp\u003eGandahusada et al. (1984) built on the knowledge about \u003cem\u003eAnopheles aconitus\u003c/em\u003e resting sites to evaluate full and selective spraying in Java, Indonesia, using fenitrothion as \u003cem\u003eAn. aconitus\u003c/em\u003e populations were becoming resistant to DDT. They designed three areas for the study, one for full spraying, one for selective spraying (between 10 and 85cm on the wall, in addition to full spraying of cattle shelters), and one for the control. Cholinesterase levels were monitored in the sprayers to prevent negative health effects from exposure to the insecticide. More sprayers in the full spray arm had \u0026gt;50% reduction in cholinesterase than those in the selective spray arm, indicating less exposure for those conducting the selective spray. The full spray arm reduced malaria slide-positive rates from 6.5% to 0.4%, while selective spray reduced the rate from 1.9% to 0.3%. However, there was a more substantial decrease in the \u003cem\u003ePlasmodium falciparum\u003c/em\u003e index (proportion of cases caused by \u003cem\u003eP. falciparum\u003c/em\u003e) in the full coverage area than in the selective spray area.\u003c/p\u003e\n\u003cp\u003eAsinas et al. (1994) observed resting heights of \u003cem\u003eAnopheles flavirostris\u003c/em\u003e in a site outside of Manila, Philippines. They found the vast majority resting below 1m on the walls and evaluated the impact of selective spraying (the lower 70cm of the wall, as well as 10cm around windows and interior and exterior eaves) in experimental huts for 6 months. They found similar results for full spraying and selective spraying, with never more than an 8% difference in mosquito mortality between the two.\u003c/p\u003e\n\u003cp\u003eArredondo Jiménez et al. (1995) evaluated full spraying and selective spraying (a horizontal swath on the wall between 0.75 and 1.75m from the floor, as well as a 1m swath of the roof from where it met the wall) with bendiocarb in Mexico. They followed the community for two years (over four spray rounds) and measured the entomological impact. They did not note substantial differences between the fully sprayed and selectively sprayed areas in terms of residual activity of the insecticide, resting behavior or mortality of \u003cem\u003eAn. albimanus\u0026nbsp;\u003c/em\u003emosquitoes, or human landing collections. They found a 50% savings in spraying time in the selective spray area and 40% overall cost savings.\u003c/p\u003e\n\u003cp\u003eColeman et al. (2021) conducted an experimental hut study coupled with a village-level study to evaluate selective spraying. The experimental hut study evaluated half walls (lower and upper) in combination with the ceiling with full spraying. There was no significant difference in mortality of \u003cem\u003eAn. gambiae s.l.\u0026nbsp;\u003c/em\u003efound between full spraying and either of the selective spraying treatments. The inclusion of the ceiling appeared to be important, as the mortality was more than 20% higher when the ceiling was included in the treatment arms. There was also no significant difference between human biting rates between full and selectively sprayed communities (upper half+ceiling), and both were significantly lower than in unsprayed communities.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eChabi et al. (2023) conducted an experimental hut trial in Côte d’Ivoire, in an area of intense pyrethroid resistance. \u0026nbsp;Three IRS insecticides (pirimiphos methyl 1g/m\u003csup\u003e2\u003c/sup\u003e (Actellic), clothianidin 300mg/m\u003csup\u003e2\u003c/sup\u003e (SumiShield) and clothianidin 200mg/m\u003csup\u003e2\u003c/sup\u003e +deltamethrin 25mg/m\u003csup\u003e2\u003c/sup\u003e(Fludora Fusion)) were evaluated with four treatments (unsprayed, fully sprayed, bottom half of the wall + ceiling, upper half of wall +ceiling). For all three insecticides, there was slightly higher mortality with the bottom half of the wall+ceiling than the upper half of the wall + ceiling. The differences in mortality between full spray and the two selective spray treatments were not statistically significant except for clothianidin, where the top half+ceiling spray resulted in less mortality than the other two treatments.\u003c/p\u003e\n\u003cp\u003eSnetselaar et al. (in preparation) evaluated selective spraying and uneven spraying in release-recapture and experimental hut studies. In the release-recapture study, \u003cem\u003eAnopheles gambiae\u003c/em\u003e Kisumu (susceptible to all insecticides tested) was released in huts with clothianidin 200mg/m2 + deltamethrin 25mg/m2 (Fludora Fusion) sprayed using a selective, checkerboard spray (50% of walls sprayed), uneven spray (some areas sprayed at 10%, others at 100%, and others at 190%), full spray (manual or with a track sprayer), as well as full spraying of pirimithos-methyl 1g/m\u003csup\u003e2\u003c/sup\u003e (Actellic). Mortality (24h) was not significantly different between any of the treatments. For the experimental hut trial with \u003cem\u003eAnopheles arabiensis\u003c/em\u003e, the highest 24 hour mortality was found with the track sprayer full spray, and the mortality was not significantly different between the other treatments.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eIRS program cost analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe percentage break down of the PMI VectorLink IRS program costs are shown in figure 1.\u003c/p\u003e\n\u003cp\u003eFor all of the publications where cost savings of IRS are reported, most authors have shown the data for reduction in insecticide use and spray team costs (mainly staff costs) (Table 2). Coleman et al. (2021) have also extrapolated that a reduction in the spray team time would also reduce the transportation costs by the same percentage, as the team could spray more houses in a day, requiring less travel to complete the same number of houses.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eUsing these assumptions, the IRS cost model was used to show the overall savings that could be achieved when the entire program costs are included, such as admin, monitoring, entomology, and community engagement. An example of the inputs and outputs from the IRS cost model are shown in Figure 2 for the results reported by Coleman et al. (2021). The overall savings when selective IRS was used ranged from 15.5-28.6% for programs which targeted \u003cem\u003eAnopheles\u003c/em\u003e mosquitoes and 17.5-41.1% for programs that targeted \u003cem\u003eAe. aegypti\u003c/em\u003e.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eSelective spraying has been repeatedly proposed as a solution to optimize the cost effectiveness and minimize the logistical challenges of IRS. Observations of patterns in the resting behavior of mosquitoes have led to the conclusion that if preferred resting places are sprayed, then a comparable impact can be achieved with less (but more targeted) spraying. As several authors have noted, this depends on using a non-irritant insecticide to ensure that mosquitoes do not avoid sprayed areas (Byford et al. 1987, Asinas et al. 1994). \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFrom some of the operational pilots and experimental hut studies, it appears that selective spraying can result in comparable results at a reduced cost. Some studies noted epidemiological impacts at reduced costs (Pletsch \u0026amp; Demos 1954, Lassen et al. 1972, Gandahusada et al. 1984), whereas other studies noted important entomological impacts (Gramiccia et al. 1953, Asinas et al. 1994, Arredondo-Jim\u0026eacute;nez et al. 1995, Coleman et al. 2021, Chabi et al. 2021). In some cases, there appeared to be a slightly reduced effect or other disadvantages such as possible selection of resistance, slower rates of decrease in malaria rates, and reluctance from homeowners (Pletsch \u0026amp; Demos 1954, Gandahusada 1984), whereas in other cases, there appeared to be advantages other than reduced costs, i.e. reduced insecticide exposure (Gandahusada et al. 1984).\u003c/p\u003e\n\u003cp\u003eAn essential part of selective spraying is the determination of what parts of houses should be sprayed and what parts of houses should not be sprayed. While in some cases, this decision has been informed by previous work, in other cases, the choice seems to be somewhat arbitrary. The two main factors that could inform selective spraying are logistical (i.e. making spraying houses easier and faster) or behavioral (using the behavior of the mosquito to target the key resting spaces).\u003c/p\u003e\n\u003cp\u003eAspects of spraying that would reduce the amount of spraying and logistical costs could include:\u003c/p\u003e\n\u003cul\u003e\n \u003cli\u003eSpraying that can be done from outside houses (i.e. eaves, animal shelters, etc.)\u003c/li\u003e\n \u003cli\u003eSpraying that doesn\u0026rsquo;t require the movement of furniture (upper halves of walls, ceilings, undersides of furniture), which may additionally benefit from increased user uptake\u003c/li\u003e\n \u003cli\u003eTargeted spraying of houses (ie. Only spraying houses at the edges of a village, near breeding sites or houses with children under five years of age)\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003eAspects of behavior that could result in reduced spraying could include monitoring the resting behavior of mosquitoes as determined through:\u003c/p\u003e\n\u003cul\u003e\n \u003cli\u003eRooms in which mosquitoes are resting (bedrooms, kitchens, bathrooms, animal shelters, etc.)\u003c/li\u003e\n \u003cli\u003eThe height of resting sites on the wall[1]\u003c/li\u003e\n \u003cli\u003eThe type of building in which mosquitoes are resting\u003c/li\u003e\n \u003cli\u003eThe amount of light (lux) present in resting site\u003c/li\u003e\n \u003cli\u003eTemperature and humidity of resting sites\u003c/li\u003e\n \u003cli\u003eAir movements\u003c/li\u003e\n \u003cli\u003eThe substrate on which mosquitoes are resting (wood, mud, clothes, furniture, etc.)(see Table 3 in Urbino et al. 1961)\u003c/li\u003e\n \u003cli\u003eThe interaction between an insecticide and a mosquito (toxicity and irritancy)\u003c/li\u003e\n \u003cli\u003eResting behavior related to seasonality (Smith 1955)\u003c/li\u003e\n \u003cli\u003eTypes of houses (wall substrate, roof material) (Msugupakulya et al. 2020)\u003c/li\u003e\n \u003cli\u003eOrientation (north, east, west, south) with respect to sun, climatic conditions\u003c/li\u003e\n \u003cli\u003eResting behavior of mosquitoes infected with \u003cem\u003ePlasmodium\u003c/em\u003e parasites.\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003eAs seen above, the behavior of mosquitoes (in combination with an understanding of logistical issues) is essential for understanding the optimal design of a selective spray program. One of the challenges for understanding the resting behavior of mosquitoes is the fact that mosquitoes may move around the inside of houses over the course of the night, but the collection of mosquitoes at dawn may only capture one aspect of this movement. Indeed, when mosquitoes have been collected at different times or monitored through observation, it has been shown that they are moving inside houses to some degree (Smith 1962, Bown et al. 1993). It is likely that mosquitoes balance the need for homeostasis (optimal temperature and humidity) (Verhulst et al. 2020) with a choice of colours and low light to be the least visible. Better methods for monitoring mosquitoes (video recording, motion sensing, collections at multiple times) may allow for better targeting of insecticides. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThis improved monitoring of resting site behavior would seem especially important for the major African malaria vectors, \u003cem\u003eAn. gambiae\u003c/em\u003e \u003cem\u003es.l.\u0026nbsp;\u003c/em\u003eand \u003cem\u003eAn. funestus\u003c/em\u003e, as there appear to be contradictory findings in the literature. The earliest recording of resting heights found most \u003cem\u003eAn. gambiae\u003c/em\u003e and \u003cem\u003eAn. funestus\u003c/em\u003e to be resting on walls below 2.1m; however, this was in \u0026ldquo;cone huts\u0026rdquo; that reached 6.4m in height (Smith 1955). Mathis et al. (1963) reported that 94.6% of \u003cem\u003eAn. gambiae\u003c/em\u003e and \u003cem\u003eAn. funestus\u003c/em\u003e collected in houses were resting on the ceiling. Mutinga et al. (1995) stated that \u003cem\u003eAn. gambiae\u003c/em\u003e rested primarily on the lower parts of walls, on fabric, and on the dark side of the room. Osae (2014) reported a number of resting sites for \u003cem\u003eAn. gambiae\u003c/em\u003e, \u003cem\u003eAn. coluzzii\u003c/em\u003e, and \u003cem\u003eAn. funestus\u003c/em\u003e. He stated that most of the \u003cem\u003eAn. gambiae\u003c/em\u003e (56%) and \u003cem\u003eAn. funestus\u003c/em\u003e (59%) were resting on roofs, roofing beams, and ceilings between 6:00 and 10:00, whereas only 25% of \u003cem\u003eAn. coluzzii\u003c/em\u003e were found there. Msugupakulya et al. (2020) found very low numbers of \u003cem\u003eAn. funestus\u003c/em\u003e (16-20%) and \u003cem\u003eAn. arabiensis\u0026nbsp;\u003c/em\u003e(8-30%) resting under metal roofs, although higher numbers of the two species when roofs were thatched (\u003cem\u003eAn. funestus\u003c/em\u003e (33-55%), \u003cem\u003eAn. arabiensis\u003c/em\u003e (43-50%)). Importantly, they noted that considerable proportions of mosquitoes in all houses were resting on \u0026ldquo;other surfaces\u0026rdquo; than walls and roofs, presenting challenges for spraying (although the movement in houses is not to be forgotten). The two most recent experimental hut studies found different results in their pre-spray collections, with the majority of \u003cem\u003eAn. gambiae\u0026nbsp;\u003c/em\u003e\u003cem\u003es.s.\u003c/em\u003e remaining in huts in northern Ghana being found on the ceiling (followed by the top half of the wall), whereas the \u003cem\u003eAn. coluzzii\u003c/em\u003e in C\u0026ocirc;te d\u0026rsquo;Ivoire were primarily resting on the bottom half of the wall (followed by the ceiling). The apparent difference in behavior might explain why in C\u0026ocirc;te d\u0026rsquo;Ivoire, in huts treated with clothianidin, the bottom half + ceiling treatment was more effective than the top half + ceiling treatment. However, there is much to be learned about the behavior of mosquitoes inside houses, and what to do when there are multiple vector species. A better understanding of this behavior will allow the development of better selective spray methods.\u003c/p\u003e\n\u003cp\u003eThe potential cost savings of selective IRS could be substantial; and reported savings in the literature range from 38-85% for insecticide use and 25.7-82% for spray team costs (wages and food). The level of cost reduction depends on the type of selective spraying employed. In some cases, the selective spraying was limited to a single band in houses (Gandahusada et al. 1984), whereas in other studies, it was only half of the wall that was excluded (Coleman et al. 2021, Chabi et al. 2023). Reductions in costs can come from reduced insecticide and reduced time required to treat houses, especially if furniture does not have to be removed, including spray pump refilling time, water collection, etc.\u003c/p\u003e\n\u003cp\u003eHowever, these reported cost savings do not consider other costs typically associated with an IRS control program, such as surveillance and monitoring, administrative staff, chemical storage, environmental assessment, equipment etc. To understand the impact of selective IRS on the total cost of an IRS program, an IRS cost model was developed from cost analysis reports of PMI VectorLink country programs. When considering other IRS program costs and accounting for savings in transport costs not reported in some publications, the overall cost savings ranged from 15.5-28.6% for programs targeting \u003cem\u003eAnopheles\u003c/em\u003e mosquitoes\u003cem\u003e.\u003c/em\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThese percentage cost savings could reduce the cost per person per year of a PMI VectorLink IRS program from USD 7.46 (average for 2020-2022) to between USD 5.33 to USD 6.19. These represent substantial cost savings of between 17 and 29%. However, the cost of IRS programs has substantially increased over the past five years, from USD 5.36 per person per year in 2018 to USD 7.69 in 2022, and therefore the impact is substantially reduced due to rising costs (Aghajanyan et al. 2023).\u003c/p\u003e\n\u003cp\u003eNot all IRS programs are run as comprehensively as PMI VectorLink programs, and they may not have all the additional costs besides transport, staff for spraying, and insecticide, which may significantly increase the relative cost advantage of selective IRS. We are unaware of other control programs tracking and publishing their total costs to be able to compare.\u0026nbsp;\u003c/p\u003e\n\u003cdiv id=\"ftn1\"\u003e\n \u003cp\u003e[1] Note that some of the studies that have measured the resting heights of mosquitoes on walls have not presented data on mosquitoes resting on the ceiling or underside of the roof.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eA clear understanding of mosquito resting behavior is key to the effectiveness of indoor residual spraying, one of the major malaria control interventions. Currently, indoor residual spraying is conducted by spraying all sprayable interior surfaces of a house to maximize the likelihood of a mosquito coming in contact with the insecticide. However, this may not be necessary if mosquitoes preferentially rest on certain surfaces of the house. This review aimed to assess the resting behavior of \u003cem\u003eAnopheles\u003c/em\u003e mosquitoes. There were no clear patterns for African malaria vectors, and standardized methods for monitoring resting behavior are necessary before a spray campaign is implemented. The existing data on selective spraying indicate that this may be a promising way of controlling malaria, but further work is necessary. The overall impact of selective IRS on control program costs could be substantial, reducing the total program costs by up to 30-40%, which could help mitigate some of the increased program costs incurred over the past few years and help maintain IRS coverage and impact. However, these cost reductions must also be carefully considered against the total cost of an IRS program, not just the spraying operations and insecticide costs.\u003c/p\u003e\n\u003cp\u003eIRS is being phased out from an increasing number of countries due to its cost despite clear evidence of effectiveness for malaria control and insecticide resistance management. Several operational studies have indicated substantial decreases in malaria prevalence using selective spraying at a fraction of the cost of full spraying. Studies that evaluate the entomological and epidemiological impact of selective spraying with existing IRS compounds are urgently required to enable this method to be fully validated and, if successful, pass on these cost savings to help maintain this important vector control tool.\u0026nbsp;\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eDDT: Dichlorodiphenyltrichloroethane\u003c/p\u003e\n\u003cp\u003eIRS: Indoor residual spraying\u003c/p\u003e\n\u003cp\u003eITN: Insecticide-treated Net\u003c/p\u003e\n\u003cp\u003ePAHO: Pan American Health Organization\u003c/p\u003e\n\u003cp\u003eWHO: World Health Organization\u003c/p\u003e\n\u003cp\u003ePMI: Presidents Malaria Initiative\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cem\u003eEthics approval and consent to participate\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eConsent for publication\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eAvailability of data and materials\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThere is no new data presented here, and all can be found in published articles. Excel files for the cost model are available upon request.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eCompeting interests\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eFunding\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThis publication is based on research funded by IVCC, which\u0026nbsp;receives the generous support of the American\u0026nbsp;people through the United States Agency for International Development (USAID),\u0026nbsp;the Bill \u0026amp; Melinda Gates Foundation,\u0026nbsp;the Swiss Agency for Development and Cooperation (SDC)\u0026nbsp;and\u0026nbsp;UK International Development funds from the UK government.\u0026nbsp;The contents, findings and conclusions contained within are those of the authors and do not necessarily reflect positions or policies of USAID, the Bill \u0026amp; Melinda Gates Foundation, the United States Government, the UK Government,\u003cem\u003e\u0026nbsp;nor SDC.\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eAuthors’ contributions\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eConceptualization: SRI, SJM. Methodology: SRI, SJM, DN (cost model). Literature review: SRI. Analysis: SRI. Writing – original draft: SRI. Development of cost model and writing: DN. Writing – review and editing: SRI, DN, JB, FT, PM, SJM. All authors read and reviewed the final version.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eAcknowledgements\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eNatalie Lissenden (IVCC) is kindly thanked for her review of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eAuthors’ information\u003c/em\u003e\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAghajanyan A, Riley M, Tesso E, Won N, Dawadi S, Longman B. April 2023. PMI IRS Country Programs: 2022 Comparative Cost Analysis. Rockville, MD. PMI VectorLink Project, Abt Associates Inc.\u003c/li\u003e\n\u003cli\u003eAsinas CY, Hugo CT, Boase CJ, Evans RG. 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WHO/UCN/GMP/2023.01 Rev1. 2023; Geneva: World Health Organization.\u003c/li\u003e\n\u003cli\u003eYukich J, Digre P, Scates S, Boydens L, Obi E, Moran N, et al. Incremental cost and cost-effectiveness of the addition of indoor residual spraying with pirimiphos-methyl in sub-Saharan Africa versus standard malaria control: results of data collection and analysis in the Next Generation Indoor Residual Sprays (NgenIRS) project, an economic-evaluation. 2022; Malar J; 21(1): 185.\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTable 1: Studies evaluating the resting sites of major African malaria vectors in houses\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"13.26530612244898%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003eReference\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003eCountry\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003eSpecies\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"29.591836734693878%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003eType of house\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.244897959183673%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003ePercentage on walls\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003ePercentage on roofs\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003ePercentage on other\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"13.26530612244898%\"\u003e\n \u003cp\u003eOsae 2014\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\"\u003e\n \u003cp\u003eGhana\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" rowspan=\"3\"\u003e\n \u003cp\u003e\u003cem\u003eAn. gambiae\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"29.591836734693878%\" valign=\"bottom\"\u003e\n \u003cp\u003eMud, brick, and cement houses with tile or metal roofs\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.244897959183673%\" valign=\"bottom\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" valign=\"bottom\"\u003e\n \u003cp\u003e56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" valign=\"bottom\"\u003e\n \u003cp\u003e35\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"14.942528735632184%\"\u003e\n \u003cp\u003eSande et al. 2016\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\"\u003e\n \u003cp\u003eZimbabwe\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"bottom\"\u003e\n \u003cp\u003eMud, brick, and cement houses with tile or metal roofs\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.793103448275861%\" valign=\"bottom\"\u003e\n \u003cp\u003e36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\" valign=\"bottom\"\u003e\n \u003cp\u003e42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\" valign=\"bottom\"\u003e\n \u003cp\u003e16\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"14.942528735632184%\" valign=\"bottom\"\u003e\n \u003cp\u003eColeman et al. 2021\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\" valign=\"bottom\"\u003e\n \u003cp\u003eGhana\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"bottom\"\u003e\n \u003cp\u003eExperimental hut, tarpaulin ceiling\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.793103448275861%\" valign=\"bottom\"\u003e\n \u003cp\u003e51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\" valign=\"bottom\"\u003e\n \u003cp\u003e45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\" valign=\"bottom\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"13.26530612244898%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"29.591836734693878%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003eMEAN\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.244897959183673%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003e32\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003e48\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003e19\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"13.26530612244898%\"\u003e\n \u003cp\u003eOsae 2014\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\"\u003e\n \u003cp\u003eGhana\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" rowspan=\"2\"\u003e\n \u003cp\u003e\u003cem\u003eAn. coluzzii\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"29.591836734693878%\"\u003e\n \u003cp\u003eMud, brick, and cement houses with tile or metal roofs\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.244897959183673%\"\u003e\n \u003cp\u003e29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\"\u003e\n \u003cp\u003e45\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"14.942528735632184%\"\u003e\n \u003cp\u003eChabi et al. 2023\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\"\u003e\n \u003cp\u003eC\u0026ocirc;te d\u0026apos;Ivoire\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\"\u003e\n \u003cp\u003eExperimental hut, plywood ceiling\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.793103448275861%\"\u003e\n \u003cp\u003e63\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\"\u003e\n \u003cp\u003e31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"13.26530612244898%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"29.591836734693878%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003eMEAN\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.244897959183673%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003e46\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003e28\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003e26\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"13.26530612244898%\"\u003e\n \u003cp\u003eOsae 2014\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\"\u003e\n \u003cp\u003eGhana\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" rowspan=\"6\"\u003e\n \u003cp\u003e\u003cem\u003eAn. funestus\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"29.591836734693878%\" valign=\"bottom\"\u003e\n \u003cp\u003eMud, brick, and cement houses with tile or metal roofs\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.244897959183673%\" valign=\"bottom\"\u003e\n \u003cp\u003e23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" valign=\"bottom\"\u003e\n \u003cp\u003e59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" valign=\"bottom\"\u003e\n \u003cp\u003e18\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"14.942528735632184%\"\u003e\n \u003cp\u003eSande et al. 2016\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\"\u003e\n \u003cp\u003eZimbabwe\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"bottom\"\u003e\n \u003cp\u003eMud, brick, and cement houses with tile or metal roofs\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.793103448275861%\" valign=\"bottom\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\" valign=\"bottom\"\u003e\n \u003cp\u003e50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\" valign=\"bottom\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"14.942528735632184%\"\u003e\n \u003cp\u003eMsugupakulya et al. 2020\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\"\u003e\n \u003cp\u003eTanzania\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"bottom\"\u003e\n \u003cp\u003eThatched roofs and mud walls, no ceiliings\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.793103448275861%\" valign=\"bottom\"\u003e\n \u003cp\u003e18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\" valign=\"bottom\"\u003e\n \u003cp\u003e55\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\" valign=\"bottom\"\u003e\n \u003cp\u003e27\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"14.942528735632184%\"\u003e\n \u003cp\u003eMsugupakulya et al. 2020\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\"\u003e\n \u003cp\u003eTanzania\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"bottom\"\u003e\n \u003cp\u003eThatched roofs and brick walls, no ceilings\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.793103448275861%\" valign=\"bottom\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\" valign=\"bottom\"\u003e\n \u003cp\u003e33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\" valign=\"bottom\"\u003e\n \u003cp\u003e43\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"14.942528735632184%\"\u003e\n \u003cp\u003eMsugupakulya et al. 2020\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\"\u003e\n \u003cp\u003eTanzania\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"bottom\"\u003e\n \u003cp\u003eMetal roofs and unplastered brick walls, no ceilings\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.793103448275861%\" valign=\"bottom\"\u003e\n \u003cp\u003e37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\" valign=\"bottom\"\u003e\n \u003cp\u003e16\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\" valign=\"bottom\"\u003e\n \u003cp\u003e47\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"14.942528735632184%\"\u003e\n \u003cp\u003eMsugupakulya et al. 2020\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\"\u003e\n \u003cp\u003eTanzania\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"bottom\"\u003e\n \u003cp\u003eMetal roofs and plastered brick walls, no ceilings\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.793103448275861%\" valign=\"bottom\"\u003e\n \u003cp\u003e27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\" valign=\"bottom\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\" valign=\"bottom\"\u003e\n \u003cp\u003e53\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"13.26530612244898%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"29.591836734693878%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003eMEAN\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.244897959183673%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003e28\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003e39\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003e32\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"13.26530612244898%\"\u003e\n \u003cp\u003eMsugupakulya et al. 2020\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\"\u003e\n \u003cp\u003eTanzania\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" rowspan=\"4\"\u003e\n \u003cp\u003e\u003cem\u003eAn. arabiensis\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"29.591836734693878%\" valign=\"bottom\"\u003e\n \u003cp\u003eThatched roofs and mud walls\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.244897959183673%\" valign=\"bottom\"\u003e\n \u003cp\u003e21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" valign=\"bottom\"\u003e\n \u003cp\u003e43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" valign=\"bottom\"\u003e\n \u003cp\u003e36\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"14.942528735632184%\"\u003e\n \u003cp\u003eMsugupakulya et al. 2020\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\"\u003e\n \u003cp\u003eTanzania\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"bottom\"\u003e\n \u003cp\u003eThatched roofs and brick walls\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.793103448275861%\" valign=\"bottom\"\u003e\n \u003cp\u003e13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\" valign=\"bottom\"\u003e\n \u003cp\u003e50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\" valign=\"bottom\"\u003e\n \u003cp\u003e38\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"14.942528735632184%\"\u003e\n \u003cp\u003eMsugupakulya et al. 2020\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\"\u003e\n \u003cp\u003eTanzania\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"bottom\"\u003e\n \u003cp\u003eMetal roofs and unplastered brick walls\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.793103448275861%\" valign=\"bottom\"\u003e\n \u003cp\u003e27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\" valign=\"bottom\"\u003e\n \u003cp\u003e8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\" valign=\"bottom\"\u003e\n \u003cp\u003e66\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"14.942528735632184%\"\u003e\n \u003cp\u003eMsugupakulya et al. 2020\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\"\u003e\n \u003cp\u003eTanzania\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.333333333333336%\" valign=\"bottom\"\u003e\n \u003cp\u003eMetal roofs and plastered brick walls\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.793103448275861%\" valign=\"bottom\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\" valign=\"bottom\"\u003e\n \u003cp\u003e30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\" valign=\"bottom\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"13.26530612244898%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"29.591836734693878%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003eMEAN\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.244897959183673%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003e18\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003e33\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.224489795918368%\" valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003e50\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;Table 2: The impact and cost savings of selective spraying studies\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"102%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"8.333333333333334%\" rowspan=\"2\"\u003e\n \u003cp\u003e\u003cstrong\u003eStudy\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\" rowspan=\"2\"\u003e\n \u003cp\u003e\u003cstrong\u003eLocation\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\" rowspan=\"2\"\u003e\n \u003cp\u003e\u003cstrong\u003eMain vector(s)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\" rowspan=\"2\"\u003e\n \u003cp\u003e\u003cstrong\u003eInsecticide\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.75%\" rowspan=\"2\"\u003e\n \u003cp\u003e\u003cstrong\u003eType of selective spraying\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.458333333333334%\" rowspan=\"2\"\u003e\n \u003cp\u003e\u003cstrong\u003eImpact of selective spraying compared with full spraying\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.25%\" rowspan=\"2\"\u003e\n \u003cp\u003e\u003cstrong\u003eReported cost savings with selective spraying (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.291666666666667%\" rowspan=\"2\"\u003e\n \u003cp\u003e\u003cstrong\u003eReduction in insecticide use (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\" colspan=\"2\"\u003e\n \u003cp\u003e\u003cstrong\u003eBased on the reduction in days required to spray an equivalent number of houses\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.416666666666666%\" rowspan=\"2\"\u003e\n \u003cp\u003e\u003cstrong\u003eOverall reduction in total operational costs (cost model) (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"57.142857142857146%\"\u003e\n \u003cp\u003e\u003cstrong\u003eReduction in spray team wages/meals (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"42.857142857142854%\"\u003e\n \u003cp\u003e\u003cstrong\u003eReduction in transport costs (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"8.421052631578947%\"\u003e\n \u003cp\u003eGramiccia et al. 1953\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003eLebanon\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003e\u003cem\u003eAn. sacharovi, An. superpictus\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003eDDT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.94736842105263%\"\u003e\n \u003cp\u003eHorizontal band spraying\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.578947368421053%\"\u003e\n \u003cp\u003eDifficult to determine, substantial decrease in all arms (including control)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.315789473684211%\"\u003e\n \u003cp\u003e31.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003e35.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.421052631578947%\"\u003e\n \u003cp\u003e26.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.315789473684211%\"\u003e\n \u003cp\u003e21.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.526315789473685%\"\u003e\n \u003cp\u003e15.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"8.421052631578947%\"\u003e\n \u003cp\u003ePletch \u0026amp; Demos 1954\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003eTaiwan\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003e\u003cem\u003eAn. minimus\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003eDDT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.94736842105263%\"\u003e\n \u003cp\u003eFocusing spraying on sleeping rooms\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.578947368421053%\"\u003e\n \u003cp\u003eAfter two rounds of spray, infant parasite rates were 0% in both arms\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.315789473684211%\"\u003e\n \u003cp\u003e25.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003e38.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.421052631578947%\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.315789473684211%\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.526315789473685%\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"8.421052631578947%\"\u003e\n \u003cp\u003eLassen et al. 1972\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003eEl Salvador\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003e\u003cem\u003eAn. albimanus\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003ePropoxur\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.94736842105263%\"\u003e\n \u003cp\u003eTwo swaths on the inner side of the roof and in the angle between the roof and the wall\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.578947368421053%\"\u003e\n \u003cp\u003eFull spraying not evaluated, but ~10% of malaria prevalence in selective spray area compared to control area\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.315789473684211%\"\u003e\n \u003cp\u003e50-60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.421052631578947%\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.315789473684211%\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.526315789473685%\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"8.421052631578947%\"\u003e\n \u003cp\u003eGandahusada et al. 1984\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003eIndonesia\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003e\u003cem\u003eAn. aconitus\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003efenitrothion\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.94736842105263%\"\u003e\n \u003cp\u003eSprayed between 10 and 85cm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.578947368421053%\"\u003e\n \u003cp\u003eSubstantial decrease in both arms, but more impact on \u003cem\u003eP. falciparum\u003c/em\u003e with full spraying.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.315789473684211%\"\u003e\n \u003cp\u003e68.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003e64.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.421052631578947%\"\u003e\n \u003cp\u003e46.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.315789473684211%\"\u003e\n \u003cp\u003e46.0*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.526315789473685%\"\u003e\n \u003cp\u003e28.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"8.421052631578947%\"\u003e\n \u003cp\u003eAsinas et al. 1994\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003ePhilippines\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003e\u003cem\u003eAn. flavirostris\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003ebendiocarb\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.94736842105263%\"\u003e\n \u003cp\u003eExperimental huts sprayed up to 0.7m on the walls, and all areas within 0.1m of the door, window, and internal and external eaves.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.578947368421053%\"\u003e\n \u003cp\u003eNever more than 8% difference in mosquito mortality compared to the fully sprayed hut\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.315789473684211%\"\u003e\n \u003cp\u003e36% spray time, 49% less insecticide\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003e49.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.421052631578947%\"\u003e\n \u003cp\u003e36.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.315789473684211%\"\u003e\n \u003cp\u003e36.0*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.526315789473685%\"\u003e\n \u003cp\u003e21.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"8.421052631578947%\"\u003e\n \u003cp\u003eArredondo-Jimenez et al. 1995\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003eMexico\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003e\u003cem\u003eAn. albimaus\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003ebendiocarb\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.94736842105263%\"\u003e\n \u003cp\u003eExperimental huts sprayed with two 1m horizontal swaths, one from 0.75-1.75cm on the walls, and one on the roof, starting at its intersection with the wall.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.578947368421053%\"\u003e\n \u003cp\u003eNo significant difference in mortality between fully sprayed and selective sprayed huts.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.315789473684211%\"\u003e\n \u003cp\u003e40.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003e40.5\u003csup\u003e\u0026dagger;\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.421052631578947%\"\u003e\n \u003cp\u003e38.5\u003csup\u003e\u0026dagger;\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.315789473684211%\"\u003e\n \u003cp\u003e38.5*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.526315789473685%\"\u003e\n \u003cp\u003e19.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"8.421052631578947%\" rowspan=\"2\"\u003e\n \u003cp\u003eDunbar et al. 2019\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\" rowspan=\"2\"\u003e\n \u003cp\u003eMexico\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\" rowspan=\"2\"\u003e\n \u003cp\u003e\u003cem\u003eAe. aegypti\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\" rowspan=\"2\"\u003e\n \u003cp\u003ebendiocarb\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.94736842105263%\" rowspan=\"2\"\u003e\n \u003cp\u003eExperimental houses sprayed on walls below 1.5m and under furniture (targeted IRS, TIRS) or under furniture only (resting site targeted IRS, RS-TIRS)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.578947368421053%\" rowspan=\"2\"\u003e\n \u003cp\u003eNo difference in first two months for RS-TIRS, or for first 4 months with TIRS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.315789473684211%\"\u003e\n \u003cp\u003eTIRS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003e38.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.421052631578947%\"\u003e\n \u003cp\u003e31.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.315789473684211%\"\u003e\n \u003cp\u003e31.0*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.526315789473685%\"\u003e\n \u003cp\u003e17.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"16.216216216216218%\"\u003e\n \u003cp\u003eRS-IRS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.91891891891892%\"\u003e\n \u003cp\u003e85.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.62162162162162%\"\u003e\n \u003cp\u003e82.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.216216216216218%\"\u003e\n \u003cp\u003e82.0*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"27.027027027027028%\"\u003e\n \u003cp\u003e41.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"8.421052631578947%\"\u003e\n \u003cp\u003eColeman et al. 2021\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003eGhana\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003e\u003cem\u003eAn. gambiae s.l.\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003epirimiphos-methyl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.94736842105263%\"\u003e\n \u003cp\u003eExperimental huts sprayed with bottom half, bottom half+ceiling, top half, top half+ceiling, or full spray. A field study that compared full spraying, selective spraying (top half+ceiling), and no spray.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.578947368421053%\"\u003e\n \u003cp\u003eNo significant differences in mortality or human biting rates between fully and selectively sprayed huts/houses. Both were better than control.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.315789473684211%\"\u003e\n \u003cp\u003e36.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.368421052631579%\"\u003e\n \u003cp\u003e39.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.421052631578947%\"\u003e\n \u003cp\u003e25.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"6.315789473684211%\"\u003e\n \u003cp\u003e25.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.526315789473685%\"\u003e\n \u003cp\u003e17.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e* extrapolated from percentage saving in spray team wages/time \u003csup\u003e\u0026dagger;\u003c/sup\u003eextrapolated from table 3 in the publication\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"malaria-journal","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"malj","sideBox":"Learn more about [Malaria Journal](http://malariajournal.biomedcentral.com/)","snPcode":"12936","submissionUrl":"https://submission.nature.com/new-submission/12936/3","title":"Malaria Journal","twitterHandle":"@malariajournal","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"selective spraying, partial spraying, indoor residual spraying, resting, Anopheles, malaria","lastPublishedDoi":"10.21203/rs.3.rs-4230947/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4230947/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cem\u003eBackground\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eIndoor residual spraying (IRS) is one of the most effective malaria control tools. However, its application has become limited to specific contexts due to the increased costs of IRS products and implementation programs. Selective spraying – selective spray targeted to particular areas/surfaces of dwellings – has been proposed to maintain the malaria control and resistance-management benefits of IRS while decreasing the costs of the intervention.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eMethods\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eA literature search was conducted to find 1) studies that assessed the resting behaviour of \u003cem\u003eAnopheles\u003c/em\u003emosquitoes and 2) studies that evaluated the impact of selective spraying on entomological and malaria outcomes. Additional articles were identified through hand searches of all references cited in articles identified through the initial search. A cost model was developed from PMI VectorLink IRS country programs, and comparative cost analysis reports to analyze the overall cost benefits of selective IRS.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eResults\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eIn some studies, there appeared to be a clear resting preference for certain \u003cem\u003eAnopheles\u003c/em\u003e species in terms of the height at which they rested. However, for other species, and particularly the major African malaria vectors, a clear resting pattern was not detected. Furthermore, resting behavior was not measured in a standardized way.\u003c/p\u003e\n\u003cp\u003eFor the selective spray studies that were assessed, there was a wide range of spray configurations, which complicates the comparison of methods. Many of these spray techniques were effective and resulted in reported 25-68% cost savings and reduced use of insecticide. The reported cost savings in the literature do not always consider all of the IRS implementation costs. Using the IRS cost model, these savings ranged from 17-29% for programs that targeted \u003cem\u003eAnopheles \u003c/em\u003esp. and 18-41% for programs that targeted \u003cem\u003eAedes aegypti\u003c/em\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eConclusions\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eResting behavior is generally measured in a simplistic way; noting the resting spot of mosquitoes in the morning. This is likely an oversimplification, and there is a need for better monitoring of resting mosquitoes. This may improve the target surface for selective spray techniques, which could reduce the cost of IRS while maintaining its effectiveness. Reporting of cost savings should be calculated considering the entire implementation costs, and we provide a cost model for future calculations.\u003c/p\u003e","manuscriptTitle":"A review of selective indoor residual spraying for malaria control","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-05-27 11:09:51","doi":"10.21203/rs.3.rs-4230947/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-06-17T09:24:54+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-06-07T05:37:59+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"90454289-9487-405b-8192-4a8b38bb78ea","date":"2024-04-17T12:07:21+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"ebf8874b-f872-409c-8d16-63fa861a064d","date":"2024-04-16T12:53:58+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-04-15T11:55:06+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-04-08T14:08:27+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-04-08T14:08:27+00:00","index":"","fulltext":""},{"type":"submitted","content":"Malaria Journal","date":"2024-04-07T10:36:16+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"malaria-journal","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"malj","sideBox":"Learn more about [Malaria Journal](http://malariajournal.biomedcentral.com/)","snPcode":"12936","submissionUrl":"https://submission.nature.com/new-submission/12936/3","title":"Malaria Journal","twitterHandle":"@malariajournal","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"a5d06c5e-614a-4d2e-b2aa-c9252789f6ba","owner":[],"postedDate":"May 27th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-08-26T15:59:59+00:00","versionOfRecord":{"articleIdentity":"rs-4230947","link":"https://doi.org/10.1186/s12936-024-05053-3","journal":{"identity":"malaria-journal","isVorOnly":false,"title":"Malaria Journal"},"publishedOn":"2024-08-23 15:57:06","publishedOnDateReadable":"August 23rd, 2024"},"versionCreatedAt":"2024-05-27 11:09:51","video":"","vorDoi":"10.1186/s12936-024-05053-3","vorDoiUrl":"https://doi.org/10.1186/s12936-024-05053-3","workflowStages":[]},"version":"v1","identity":"rs-4230947","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4230947","identity":"rs-4230947","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}