Effect of passive and active ventilation on malaria mosquito house entry and human comfort: an experimental study in rural Gambia

Abstract

Rural houses in sub-Saharan Africa are typically hot and allow malaria mosquitoes inside. We assessed whether passive or active ventilation can reduce house entry of malaria mosquitoes and cool a bedroom at night in rural Gambia. Two identical experimental houses were used: one ventilated and one unventilated (control). We evaluated the impact of (i) passive ventilation (solar chimney) and (ii) active ventilation (ceiling fan) on the number of mosquitoes collected indoors and environmental parameters (temperature, humidity, CO₂, evaporation). Although the solar chimney did not reduce entry of Anopheles gambiae sensu lato, the ceiling fan reduced house entry by 91% compared with the control house. There were no differences in indoor nightly temperature, humidity or CO₂ between intervention and control houses in either experiment. The solar chimney did not improve human comfort assessed using psychrometric analysis. While the ceiling fan improved human comfort pre-midnight, in the morning it was too cool compared with the control house, although this could be remedied through provision of blankets. Further improvements to the design of the solar chimney are needed. High air velocity in the ceiling fan house probably reduced mosquito house entry by preventing mosquito flight. Improved ventilation in houses may reduce malaria transmission.

Keywords: Africa; house design; human comfort; malaria; mosquito; ventilation.

Figure 1.

Air movement through the solar chimney. Where 1 = corrugated metal roof at wall level, 2 = hot air outlet, 3 = transparent corrugated sheet, 4 = wood frame, 5 = mud-brick wall (painted black on the outside), 6 = thatch inside plywood frames, 7 = plywood isolation frame, 8 = wall hole to allow air flow, 9 = concrete plinth, and red arrows show circulation of hot air. Dotted lines represent section elements that are not coloured for better understanding.

Figure 2.

Position of solar chimney and data loggers in experimental houses. Where A = temperature loggers inside the solar chimney and centre of the house, B = insulated wall, C = light trap, D = evaporimeter and E = CO₂ logger. Data loggers recording ambient temperature and CO₂ were placed in a Stevenson screen between the two experimental houses (not shown).

Figure 3.

Experimental house with solar chimney on southeast facing wall (a) and extended roof on northwest elevation (b).

Figure 4.

Mean mosquito numbers per night recorded for solar chimney experiment. For female An. gambiae s.l., female Mansonia spp. and all female mosquitoes (Anopheles spp., Mansonia spp., Culex spp. and Aedes spp.).

Figure 5.

Indoor and outdoor temperatures recorded during the solar chimney experiment. Where mean outdoor temperature = dotted line, indoor temperature in control hut = light green line, indoor temperature in solar chimney house = orange line, temperature in solar chimney = dark green line, night = grey section and duration of experimental night = red line.

Figure 6.

Average indoor and outdoor night-time CO₂ concentrations recorded during the solar chimney experiment. Where outdoor levels = dotted line, control house = turquoise line and house with solar chimney = orange line.

Figure 7.

Psychrometric charts showing the human comfort index of adults in houses with and without a solar chimney, and with and without a ceiling fan. (a) Readings, shown as coloured polygons, made from 21.00 to 23.59. (b) Readings made from 00.00–06.00. Human comfort analysis for the ceiling fan assumes an air velocity experienced by the sleeper of 0.36 and 0.0 m s⁻¹ for the solar chimney house and control houses. Each data point represents a combination of temperature and relative humidity (and air velocity for ceiling fan) at different times of the night. Data points that fall within the black polygons represent values that are known to be comfortable for lightly dressed adults sitting or sleeping. Data to the left of the polygon represents values that will be perceived as too cold while data to the right will be considered too hot. Values in red indicate the percentage of readings deemed to be comfortable.

Figure 8.

CFD simulations of (a) CO₂ distribution and (b) indoor temperature in the house without (i) and with (ii) solar chimney. The solar chimney is depicted in (ii) as an additional rectangular shape adjoining the house. CO₂ distributions shown are at the height of the two sleeping adults.

Figure 9.

Mean mosquito numbers per night recorded for ceiling fans experiment. For female An. gambiae s.l., female Mansonia spp. and all female mosquitoes (Anopheles spp., Mansonia spp., Culex spp. and Aedes spp.).

Figure 10.

Average indoor and outdoor temperatures recorded during experimental night of the ceiling fans experiment. Outside (dotted line), control hut (turquoise line) and intervention hut (orange line).

Figure 11.

Average indoor and outdoor night-time CO₂ concentrations recorded during the ceiling fan experiment. Outside (dotted line), house with fan turned off (turquoise line) and house with fan turned on (orange line).

Figure 12.

CFD simulations of air flow in the experimental house with no ceiling fan (a) and with the ceiling fan operational (b). The ceiling fan of diameter 1.40 m is depicted in (b) with a red dashed circle. CO₂ distributions shown are at the height of the two sleeping adults.