The impact of different housing designs on mosquito house entry in The Gambia

Executive Summary Background Although 80-100% of malaria transmission occurs indoors in sub-Saharan Africa, little is known about how changes to the design of houses affects this risk. Simple house modifications can affect house occupant’s exposure to malaria mosquitoes in rural houses in sub-Saharan Africa. This is important since Africa’s housing stock is changing rapidly from the traditional thatched roofed houses with open eaves to metal-roofed houses with closed eaves. In order to study the effect of different housing features on mosquito house entry I carried out a series of experiments using five single-roomed experimental houses with different housing typologies in Wellingara village, The Gambia. It was also important to consider how the different typologies affected indoor climate since a hot house is likely to reduce the use of long-lasting insecticidal nets indoors. These experiments were conducted to address the following questions; 1. What is the impact of different housing typologies on mosquito house entry and indoor climate? 2. What effect do different gaps around the doors have on mosquito house entry in houses with closed eaves? 3. Are small and large screened windows effective in reducing mosquito house entry in houses with closed eaves and badly-fitting doors? Methods The five single-roomed experimental houses were the average size of a single-roomed house in The Gambia built from mud block walls. Three experiments were run. The first experiment tested five different housing typologies: 1) thatched roof, open eaves, badly-fitting unscreened doors; 2) thatched roof, closed eaves, badly-fitting unscreened doors; 3) thatched roof, closed eaves, screened louvered metal doors; 4) metal roof, closed eaves, badly-fitting unscreened doors and 5) a novel ventilated metal roof house, with closed eaves, screened gable windows and screened louvered metal doors. The second experiment investigated the role of gaps around doors in mosquito house entry in houses with closed eaves. The third experiment examined the effect of different sizes and numbers of screened windows in houses with closed eaves and badly-fitting doors. Each experiment ran for five weeks and at the end of each five nights, the building materials were rotated between the houses using a replicated Latin rectangle design. In the first experiment, one healthy adult man slept in each house under a treated bed net (Olyset) for five weeks, whilst in the other experiments two healthy adult men slept in each house each night. In each experiment mosquitoes were collected nightly from each house using a CDC light trap. In the first experiment data loggers were used to measure temperature and relative humidity through the day. Findings In the first experiment, closing the eaves in thatch-roofed houses with badly-fitting doors reduced the number of Anopheles gambiae s.l. by 94% (Odds ratio (OR)=0.058, 95% confidence intervals (CI)=0.03-0.11) compared with the traditional thatched-roofed houses with open eaves. A similar reduction in mosquito house entry was also found in thatched-roofed houses with well-fitting screened doors. However, closing the eaves of metal-roofed houses did not reduce the number of mosquitoes entering the house compared to the thatched-roofed house with open eaves. Nonetheless, the number of mosquitoes collected in metal-roofed houses with closed eaves was reduced by 94% (OR=0.057, 95% CI=0.03-0.10) when well-fitting screened doors were added to the building. Similar reductions were observed in other Anopheles spp., Culex spp. and Mansonia spp. There was no significant different in night time mean temperature between thatch roofed, open eaves and the ventilated metal-roofed house with closed eaves, screened doors and windows (thatch roofed, open eaves mean temperature=33.08oC, 95% CI=32.58-33.58oC; ventilated metal-roofed house with closed eaves, screened doors and windows mean temperature=33.81oC, 95% CI=33.25-34.37oC). Whilst it was hotter in metal-roofed houses with closed eaves (mean temperature=34.72oC, 95% CI=34.06-35.39oC) than thatched-roofed houses with open eaves (mean temperature=33.08oC, 95% CI=32.58-33.58oC). In the second experiment, the number of An. gambiae s.l. entering houses was not affected by having a single gap above or below the door compared with houses with gaps at both the top and bottom of the door. However, the number of Culex spp. and Mansonia spp. were reduced if the gap was above the door. In the third experiment, the number of An. gambiae s.l. entering metal-roofed houses with badly fitting doors was reduced as the area of screened window increased. Similar reductions were observed in other Anopheles, Culex spp. and Mansonia spp.. Interpretation These findings demonstrate that design of a house affects mosquito-house entry. Reductions in An. gambiae s.l. can be achieved by closing the eaves of thatched-roofed houses or adding screened doors to metal-roofed houses with closed eaves. Screened doors and windows will help keep the house cool at night and may lead to great bed net use at hot times of the year. Increasing the number of screened windows to a house will reduce house entry of malaria vectors entering badly-fitting doors. Thus housing features such as closed eaves, screened doors and windows should be included in new buildings

Status of insecticide resistance in Anopheles gambiae (s.l.) of The Gambia.

BACKGROUND: Vector control activities, namely long-lasting insecticidal nets (LLIN) and indoor residual spraying (IRS), have contributed significantly to the decreasing malaria burden observed in The Gambia since 2008. Nevertheless, insecticide resistance may threaten such success; it is important to regularly assess the susceptibility of local malaria vectors to available insecticides. METHODS: In the transmission seasons of 2016 and 2017, Anopheles gambiae (s.l.) larvae were sampled in or around the nine vector surveillance sentinel sites of the Gambia National Malaria Control Programme (GNMCP) and in a few additional sampling points. Using WHO susceptibility bioassays, female adult mosquitoes were exposed to insecticide-impregnated papers. Molecular identification of sibling species and insecticide resistance molecular markers was done on a subset of 2000 female mosquitoes. RESULTS: A total of 4666 wild-caught female adult mosquitoes were exposed to either permethrin (n = 665), deltamethrin (n = 744), DDT (n = 1021), bendiocarb (n = 990) or pirimiphos-methyl (n = 630) insecticide-impregnated papers and control papers (n = 616). Among the 2000 anophelines, 1511 (80.7%) were Anopheles arabiensis, 204 (10.9%) Anopheles coluzzii, 75 (4%) Anopheles gambiae (s.s.), and 83 (4.4%) An. gambiae (s.s.) and An. coluzzii hybrids. There was a significant variation in the composition and species distribution by regions and year, P = 0.009. Deltamethrin, permethrin and DDT resistance was found in An. arabiensis, especially in the coastal region, and was mediated by Vgsc-1014F/S mutations (odds ratio = 34, P = 0.014). There was suspected resistance to pirimiphos-methyl (actellic 300CS) in the North Bank Region although only one survivor had the Ace-1-119S mutation. CONCLUSIONS: As no confirmed resistance to bendiocarb and actellic 300CS was detected, the national malaria control programme can continue using these insecticides for IRS. Nevertheless, the detection of Ace-1 119S mutation warrants extensive monitoring. The source of insecticide pressure driving insecticide resistance to pyrethroids and DDT detected at the coastal region should be further investigated in order to properly manage the spread of resistance in The Gambia

Recommendations for building out mosquito-transmitted diseases in sub-Saharan Africa: the DELIVER mnemonic

In sub-Saharan Africa, most transmission of mosquito-transmitted diseases, such as malaria or dengue, occurs within or around houses. Preventing mosquito house entry and reducing mosquito production around the home would help reduce the transmission of these diseases. Based on recent research, we make key recommendations for reducing the threat of mosquito-transmitted diseases through changes to the built environment. The mnemonic, DELIVER, recommends the following best practices: (i) Doors should be screened, self-closing and without surrounding gaps; (ii) Eaves, the space between the wall and roof, should be closed or screened; (iii) houses should be Lifted above the ground; (iv) Insecticide-treated nets should be used when sleeping in houses at night; (v) houses should be Ventilated, with at least two large-screened windows to facilitate airflow; (vi) Environmental management should be conducted regularly inside and around the home; and (vii) Roofs should be solid, rather than thatch. DELIVER is a package of interventions to be used in combination for maximum impact. Simple changes to the built environment will reduce exposure to mosquito-transmitted diseases and help keep regions free from these diseases after elimination

Research agenda for preventing mosquito-transmitted diseases through improving the built environment in sub-Saharan Africa

Mosquito-transmitted diseases are a major threat to health in sub-Saharan Africa, but could be reduced through modifications to the built environment. Here we report findings from a major workshop held to identify the research gaps in this area, namely: (1) evidence of the health benefits to changes to the built environment, (2) understanding how mosquitoes enter buildings, (3) novel methods for reducing mosquito-house entry, (4) sustainable approaches for reducing mosquito habitats, (5) case studies of micro-financing for healthy homes and (6) methods for increasing scale-up. Multidisciplinary research is essential to build out mosquito-transmitted diseases, and not build them in

The Use of Chemical Weapons: The United States Response and Strategies in The Syrian civil War

This research aims at exploring the use of chemical weapons in the Syrian conflict, in particular, the dilemma of the American policymakers in response to the use of prohibited weapons in the Syrian conflict. The use of chemical weapons in Syria has been a major source of tension, but one could wonder what were the strategies employed by the US in responding to use of chemical weapons in Syria. Syrian crisis has been marked by a number of horrible acts of conventional violence, we can see that this conventional brutality was insufficient to lead to the US interventionist foreign policy. Why was it thought that the use of chemical weapons would determine whether or not the US would intervene militarily? These are some of the issues that this paper typically identifies. The study collected, examined, and analyzed secondary data on the US response using a qualitative case study approach. The arguments produced in this study were based on three theoretical frameworks: constructivism, strategic narrative, and framing concept. According to the study's findings, there have been three major strategies. The US utilized framing, the taboo against chemical weapons, and intervention strategies in carrying out a response to the use of chemical weapons in Syria

Effect of roof colour on indoor temperature and human comfort levels, with implications for malaria control: a pilot study using experimental houses in rural Gambia

Background In rural sub-Saharan Africa, thatch roofs are being replaced by metal roofs. Metal roofing, however, increases indoor temperatures above human comfort levels, and thus makes it more likely that residents will not use an insecticide-treated bed net (ITN) at night. Whether the colour of a metal roof affects indoor temperature and human comfort was assessed. Methods Two identical, experimental houses were constructed with metal roofs in rural Gambia. Roof types were: (1) original bare-metal, (2) painted with red oxide primer or (3) white gloss, to reflect solar radiation. Pairwise comparisons were run in six, five-night blocks during the malaria season 2018. Indoor climate was measured in each house and multivariate analysis used to compare indoor temperatures during the day and night. Results From 21.00 to 23.59 h, when most residents decide whether to use an ITN or not, the indoor temperature of a house with a bare metal roof was 31.5 °C (95% CI  31.2–31.8 °C), a red roof, 30.3 °C (95% CI 30.0–30.6) and a white roof, 29.8 °C (95% CI 29.4–30.1). During the same period, red-roofed houses were 1.23 °C cooler (95% CI 1.22–1.23) and white roofs 1.74 °C cooler (95% CI 1.70–1.79) than bare-metal roofed houses (p  < 0.001). Similar results were found from 00.00 to 06.00 h. Maximum daily temperatures were 0.93 °C lower in a white-roofed house (95% CI  0.10–0.30, p  < 0.001), but not a red roof (mean maximum temperature difference  = 0.44 °C warmer, 95% CI  0.43–0.45, p  = 0.081), compared with the bare-metal roofed houses. Human comfort analysis showed that from 21.00 to 23.59 h houses with white roofs (comfortable for 87% time) were more comfortable than bare-metal roofed houses (comfortable for 13% time; odds ratio  = 43.7, 95% CI 27.5–69.5, p  < 0.001). The cost of painting a metal roof white is approximately 31–68 USD. Conclusions Houses with a white roof were consistently cooler and more comfortable than those with a bare metal roof. Painting the roofs of houses white is a cheap way of making a dwelling more comfortable for the occupants and could potentially increase bed net use in hot humid countries

Measuring ventilation in different typologies of rural Gambian houses: a pilot experimental study

Background: African houses are frequently too hot and uncomfortable to use a bed net at night. Indoor thermal comfort is often evaluated by measuring temperature and humidity, ignoring ventilation. This study explored ways to measure ventilation in single-roomed rural Gambian houses during the malaria transmission season and evaluated building designs that could increase airflow at night and help keep the occupants comfortable. Methods: Two identical mud-walled houses were constructed with a metal roof, three doors and closed eaves. Experiment 1 compared five methods for measuring ventilation in a building: (1) using a blower door, (2) increasing carbon dioxide (CO2) levels indoors using an artificial source of CO2 and then measuring the rate of gas decay, (3) using a similar approach with a natural source of CO2, (4) measuring the rise of CO2 when people enter a building and (5) using hot-wire anemometers. Experiment 2 used CO2 data loggers to compare ventilation in a reference metal-roofed house with closed eaves and badly-fitting doors with a similar house with (1) thatched roof and open eaves, (2) eaves tubes, (3) screened doors and (4) screened doors and windows. Results: In experiment 1, CO2 data loggers placed indoors in two identical houses showed similar changes in airflow (p > 0.05) for all three methods recording either decreasing or increasing CO2. Blower doors were unable to measure airflow in houses with open eaves or screened windows and the anemometers broke down under field conditions. In experiment 2, open eaves in thatched houses, screened doors alone, and screened doors and windows increased indoor ventilation compared to the reference metal-roofed house with closed eaves and badly fitting doors (p < 0.05). Eaves tubes did not increase ventilation in comparison to the reference house. Conclusion: CO2 data loggers proved to be a simple and efficient method for measuring ventilation in rural houses at night. Ventilation of metal-roofed houses can be improved by adding two screened doors and windows on opposite walls. Improved ventilation will result in increased thermal comfort making it more likely that people will sleep under a bed net

How house design affects malaria mosquito density, temperature, and relative humidity: an experimental study in rural Gambia

Introduction: Unprecedented improvements in housing are occurring across much of rural sub-Saharan Africa, but the consequences of these changes on malaria transmission remain poorly explored. We examined how different typologies of rural housing affect mosquito house entry and indoor climate. Methods: Five typologies of mud-block houses were constructed in rural Gambia: four were traditional designs with poorly fitted doors and one was a novel design with gable windows to improve ventilation. In each house, one male volunteer slept under a bednet and mosquitoes were collected indoors with a light trap. Typologies were rotated between houses weekly. Indoor conditions were monitored with data loggers and the perceived comfort of sleepers recorded with questionnaires. We used pyschrometric modelling to quantify the comfort of the indoor climate using the logger data. Primary measurements were mean number of Anopheles gambiae and mean temperature for each house typology. Findings: In thatched-roofed houses, closing the eaves reduced A gambiae house entry by 94% (95% CI 89–97) but increased the temperature compared with thatched-roofed houses with open eaves. In houses with closed eaves, those with metal roofs had more A gambiae, were hotter (1·5°C hotter [95% CI 1·3–1·7]) between 2100h and 2300 h, and had 25% higher concentrations of carbon dioxide (211·1 ppm higher [117·8–304·6]) than those with thatched roofs. In metal-roofed houses with closed eaves, mosquito house entry was reduced by 96% (91–98) by well fitted screened doors. Improved ventilation of metal-roofed houses made them as cool as thatched houses with open eaves. Metal-roofed houses with closed eaves were considered more uncomfortable than thatched ones with closed eaves. In metal-roofed houses, ventilated houses were more comfortable than unventilated houses before midnight, when people retired to bed. Interpretation: Closing the eaves reduced vector entry in thatched houses but increased entry in metal-roofed houses. Metal-roofed houses with closed eaves were, however, protected against malaria vectors by well fitted screened doors and were made comfortable by increasing ventilation. House designs that exclude mosquitoes and are comfortable to live in should be a priority in sub-Saharan Africa

New Prototype Screened Doors and Windows for Excluding Mosquitoes from Houses: A Pilot Study in Rural Gambia

Despite compelling evidence that modern housing protects against malaria, houses in endemic areas are still commonly porous to mosquitoes. The protective efficacy of four prototype screened doors and two windows designs against mosquito house entry, their impact on indoor climate, as well as their use, durability and acceptability was assessed in a Gambian village. A baseline survey collected data on all the houses and discrete household units, each consisting of a front and back room, were selected and randomly allocated to the study arms. Each prototype self-closing screened door and window was installed in six and 12 units, respectively, with six unaltered units serving as controls. All prototype doors reduced the number of house-entering mosquitoes by 59–77% in comparison with the control houses. The indoor climate of houses with screened doors was similar to control houses. Seventy-nine percentage of door openings at night occurred from dusk to midnight, when malaria vectors begin entering houses. Ten weeks after installation the doors and windows were in good condition, although 38% of doors did not fully self-close and latch (snap shut). The new doors and windows were popular with residents. The prototype door with perforated concertinaed screening was the best performing door because it reduced mosquito entry, remained fully functional, and was preferred by the villagers. Screened doors and windows may be useful tools for reducing vector exposure and keeping areas malaria-free after elimination, when investment in routine vector control becomes difficult to maintain