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

Abstract

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.

Funding: Sir Halley Stewart Trust, Global Clinical Trials, and Global Challenges Research Fund.