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Thursday, July 25, 2024

Raised houses may reduce malaria transmission in Africa

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There is growing evidence that house design can decrease the force of malaria infection. In a new publication in the Journal of The Royal Society Interface, researchers from the United Kingdom, Denmark and The Gambia reveal that raised buildings may help reduce malaria transmission in Africa.

Despite being preventable, malaria remains an important public health challenge. The World Health Organisation (WHO) reports that overall progress in malaria control has plateaued for the first time since the turn of the century.

In 2019, there were 384,000 deaths from malaria in sub-Saharan Africa, representing 94% of the global total. In this region, around 80% of malaria infections are acquired indoors at night.

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In the 1970s, researchers in The Gambia showed that most mosquitoes fly low to the ground, tracking plumes of carbon dioxide from human hosts. Hence, preventing mosquitoes from getting indoors could be a simple way of protecting people from this often-lethal disease.

Majo Carrasco-Tenezaca from the Department of Biosciences at Durham University in the UK, in collaboration with researchers from the Medical Research Council Unit The Gambia at the London School of Hygiene & Tropical Medicine (MRCG at LSHTM), and the Royal Danish Academy in Denmark, concluded an experimental study in rural Gambia on the relationship between house height and mosquito house entry.

The primary objectives were to determine whether mosquito-hut entry declined with increasing height, and to find out whether an elevated hut would be cooler than one closer to the ground.

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The team built four experimental houses – Star Homes – in The Gambia, each of which could be raised or lowered above the ground. Each week, one hut was on the ground, while the bottoms of the other huts were at 1m, 2m and 3m. Each night, two men slept under separate mosquito nets in each hut and mosquitoes were collected indoors using a light trap. Each week the height of each house was changed, so that at the end of the 40-night experiment, each hut had been at each of the four heights for 10 nights.

The researchers found that increasing the height of a hut progressively reduced the number of mosquitoes entering the hut, such that at 3 metres above the ground, 84% fewer malaria mosquitoes entered the building compared with the hut on the ground. This may be due to two reasons: malaria mosquitoes have evolved to find humans on the ground; and at higher heights, the carbon dioxide odour plumes coming out of the huts are rapidly dispersed by the wind, so mosquitoes find it more difficult to find a person to bite.

To date, indoor residual spraying (IRS) and insecticide-treated nets (ITNs) have been the most widely used malaria vector control tools, and studies have suggested that they have made a notable contribution to the reductions in malaria observed in the early 21st century.

Evidently, these tools are insufficient to eliminate malaria. It is generally recognised that supplementary measures are needed to further decrease malaria in the region. The results of this study, therefore, has real world implications, with plans to develop prototypes based on the experimental huts. The researchers are keen to promote the use of two-storey buildings across sub-Saharan Africa, with the possibility to reduce the entry of malaria mosquitoes and also keep the occupants cool at night so they won’t be too hot to sleep under a bed net.

The Star Home is designed not only to protect children against malaria, but also to protect them against the other two main killer diseases of children: respiratory infections and diarrhoeal diseases. Another trial is underway to compare the rates of disease in children living in 110 Star homes and 440 traditional homes in Tanzania.


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