Cochrane Infectious Diseases has produced dozens of reviews on the prevention and treatment of malaria. These include interventions, such as drugs, taken by people, as well as some at the level of the environment. One of these looks at house modifications for preventing malaria and we asked lead author, Tilly Fox from the Liverpool School of Tropical Medicine in the UK to tell us about the importance of the October 2022 update and its findings.
Mike: Hello, I'm Mike Clarke, podcast editor for the Cochrane Library. Cochrane Infectious Diseases has produced dozens of reviews on the prevention and treatment of malaria. These include interventions, such as drugs, taken by people, as well as some at the level of the environment. One of these looks at house modifications for preventing malaria and we asked lead author, Tilly Fox from the Liverpool School of Tropical Medicine in the UK to tell us about the importance of the October 2022 update and its findings.
Tilly: Malaria is a life-threatening parasitic disease transmitted by female Anopheles mosquitoes. One form, Plasmodium falciparum is responsible for most malaria deaths, and 96% of those deaths occur in Africa. Although malaria can be prevented, the World Health Organization reports that overall progress in malaria control appears to have plateaued for the first time since the start of this century, and this was exacerbated by the COVID-19 pandemic. In sub-Saharan Africa, the major malaria vectors are endophilic (resting and inhabiting indoors), endophagic (indoor-biting), and night-biting. These characteristics mean that most malaria transmission occurs indoors at night.
People have used wire gauze as a screen on their homes to protect against flying insects since before it was known that mosquitoes transmitted malaria and a study published in 1901 among railway workers in Italy showed benefits from mechanical protection of houses using simple screening techniques combined with covering exposed skin and use of antimalarial drugs. The families in the study experienced less fever compared to the previous year when no house modifications were used. Since then, several studies have investigated how homes can be modified to prevent malaria, either through modifications to existing homes, such as screening windows, doors and eaves, or in the design, detailing and material specifications for new homes. This might include building taller houses where mosquitoes may not be able to enter the higher levels.
In our review update, we focused on modifications to existing homes and identified seven trials that investigated the effect on malaria. All the studies used screening as the intervention. One study also replaced thatched roofs with metal, and another added the installation of eave tubes to lure and kill mosquitoes to the screening. These studies were conducted across sub-Saharan Africa and recruited both adults and children.
Five of the studies reported the effect of the house modifications on the prevalence of parasites in the blood of people living in the modified houses. The combined findings suggested that the modifications probably reduce parasite prevalence by around 30% compared to unmodified houses. A very similar effect was seen for anaemia, which is often caused by malaria in these settings, particularly in children. The combined findings of three trials suggested that modifications to the home reduce anaemia prevalence by 30%.
Another important outcome for our review was the incidence of clinical malaria. Three trials reported this but the substantial heterogeneity among them meant that we did not pool their findings and their results ranged from a 68% increase in screened houses to a 62% decrease. Such a large increase in malaria incidence is unexpected, and when we assessed the results using the GRADE system, we were concerned about indirectness of the findings and rated this as very low certainty evidence. Finally, pooling the results of four trials that reported the density of adult mosquitoes captured indoors at night, suggested that house modifications may reduce this.
In summary, this update of our review adds substantive evidence to the previous version and supports the findings of other meta-analyses about the effectiveness of house modifications for preventing malaria. The trials show that modifications to existing homes, particularly simple techniques such as screening, can protect against anaemia and may reduce parasite prevalence for both children and adults. Further research will help delineate the best implementation approaches and the success of modifications will likely be affected by perceived benefits by users, the cost of implementation and the ability of home owners to introduce the modifications themselves.
Mike: If you would like to read this update and watch for future updates if that further research is done, it's available free at Cochrane Library dot com. Just go to the website and search 'House modifications and malaria' to find it.