The relationship between house height and mosquito house entry: an experimental study in rural Gambia

Abstract

Most malaria infections in sub-Saharan Africa are acquired indoors, thus finding effective ways of preventing mosquito house entry should reduce transmission. Since most malaria mosquitoes fly less than 1 m from the ground, we tested whether raising buildings off the ground would prevent the entry of Anopheles gambiae, the principal African malaria vector, in rural Gambia. Nightly collections of mosquitoes were made using light traps from four inhabited experimental huts, each of which could be moved up or down. Mosquito house entry declined with increasing height, with a hut at 3 m reducing An. gambiae house entry by 84% when compared with huts on the ground. A propensity for malaria vectors to fly close to the ground and reduced levels of carbon dioxide, a major mosquito attractant, in elevated huts, may explain our findings. Raised buildings may help reduce malaria transmission in Africa.

Keywords: Anopheles gambiae; housing; malaria; mosquitoes; sub-Saharan Africa.

Figure 1.

Experimental huts. From left to right, at 1 m, 3 m, 0 m and 2 m. Automatic weather station is shown to the right of the huts and the village to the left and rear.

Figure 2.

Mean mosquito house entry in huts at different heights. Error bars are 95% confidence intervals. (a) An. gambiae s.l., (b) Mansonia spp., (c) Culex quinquefasciatus and (d) all mosquitoes.

Figure 3.

Mean indoor and outdoor temperatures from 21.00 to 07.00. Where purple line = hut at 0 m, red line = hut at 1 m, green line = hut at 2 m, turquoise line = hut at 3 m and dashed black line = outside temperature.

Figure 4.

Mean carbon dioxide concentration from 21.00 to 07.00. Where purple line = hut at 0 m, red line = hut at 1 m, green line = hut at 2 m and turquoise line = hut at 3 m.

Figure 5.

Raised and two-storey constructions in sub-Saharan Africa. (a) Dogon granaries in Mali, 2016 (Hamaji Magazine); (b) granaries for crop storage in Chad, 2017 (UN Environment Programme); (c) Makoko in Nigeria, 2016 (The Guardian); (d) Ganvie in Benin, 2018 (Scribol Magazine); (e) double-storey bamboo prototype house in Tanzania [15]; (f) two-storey house with store in the ground floor in Uganda (S.W.L.).