NEW FINDINGS: Improved ventilation, lighting in houses can help control malaria transmission
An experimental hut study done at Ifakara Health Institute has revealed that improved house designs that provide for better indoor lighting and ventilation can reduce the number of mosquitoes entering a house and thereby help in controlling malaria in sub-Saharan Africa.
The Malaria Journal published results from this study on its February 5th 2022 edition. Ifakara researchers who contributed to the publication are: Arnold Mmbando, Deogratius Kazimbaya, Robert Kasubiri, Doreen Siria, and Fredros Okumu. Researchers from partner institutions who had also contributed are: John Bradley (from London School of Hygiene & Tropical Medicine, UK), Jakob Knudsen (Royal Danish Academy, Denmark), Lorenz von Seidlein (Mahidol University, Thailand), and Steve Lindsay (Durham University, UK).
The study hypothesized that indoor lighting, visible from the outside, would increase the entry of Anopheles arabinoses, an important malaria vector, and examined whether ventilation modifies this effect. It was conducted at Mosquito City, Ifakara Health Institute’s semi-field system, located near Kining’ina village in Tanzania.
Four inhabited experimental huts, each situated within a large chamber, were used to assess how light and ventilation affect the number of hut-entering mosquitoes. The results showed an 84% increase in the odds of collecting mosquitos indoors when indoor light was visible outside the huts compared with when the light was not visible.
Adults aged 18-35 years were recruited for the study and each had to sleep in a new healthy house, known as a Star home. Three experiments were carried out using four experimental huts each occupied by one person. 300, unfed five-to-eight-day old female laboratory-reared An. arabiensis were released each night 3 meters from the front door of each hut. The next day, mosquitoes were collected and counted once sleepers had left the huts.
The three experiments were designed differently in order to compare results. Experiment 1 assessed whether more mosquitoes entered huts with light-permeable walls compared to those with opaque walls. Experiment 2 assessed whether the small-roof openings increased mosquito entry and Experiment 3 assessed mosquito entry in well-ventilated, Star home-type huts compared to the poorly-ventilated huts, which resembled traditional houses.
Finding from the three experiments revealed that more mosquitos entered the huts with light-permeable walls than those with opaque walls and despite the small roof openings which should have increased mosquitoes entering the huts, the air-permeable walls in these hats resulted in few mosquito entries. The odds of collecting mosquitoes were 99% less in well-ventilated huts, compared with poorly-ventilated traditional huts.
From the study findings, the researchers suggested increasing ventilation in buildings which substantially reduces mosquito entry. Most importantly, the study findings add to the literature suggesting that increasing ventilation in houses in sub-Saharan Africa may contribute to a reduction in malaria transmission, will dilute the carbon dioxide concentration indoors, and also make bedrooms cooler at night which will make it more likely for people to sleep under a bed net.
In sub-Saharan Africa, most malaria transmission occurs indoors at night. Factors such as the design of a house, its height above ground, and the degree of crowding in a building affect house entry by malaria mosquitoes. Additionally, mosquito attraction also depends on how carbon dioxide produced by dwellers emanates from a house. This gas is a major mosquito attractant.
The study was approved by Ifakara Health Institute’s Institution Review Board, Medical Research Coordinating Council at Tanzania National Institute of Medical Research, and the Department of Biosciences Ethics Committee, Durham University.