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Spatial Repellent-Treated Fabrics Could Protect Against Malaria Infection

International study led by Duke-NUS scientists finds that transfluthrin-treated fabric effectively repels Anopheles mosquitoes that transmit malaria.

Among disease types transmitted by mosquitoes, malaria is perhaps one of the most well-known. According to the World Malaria Report from the World Health Organisation, while much progress has been made to eradicate malaria between 2010, and 2018, progress seems to be approaching a plateau. The worldwide incidence rate has remained at around 57 per 1000 population at risk since 2014, and malaria continues to cause nearly half a million deaths worldwide annually. Although the vast majority of malaria cases were seen in Africa, 3.4 percent of malaria cases in 2018 were in Southeast Asia, where unfortunately, the malaria parasite Plasmodium falciparum exhibits resistance to combination drug therapy.

Plasmodium parasites that causes malaria are carried by malaria vectors, in particular the female Anopheles mosquitoes. Current measures in malaria control include distributing insecticide-treated mosquito nets, rapid diagnostic tests, and artemisinin-based combination therapy (ACT). However, insecticide and drug resistance are on the rise, a worrying trend that could undermine efforts in the global fight against malaria.

A study led by Duke-NUS Medical School (Duke-NUS) aims to reduce malaria incidence by targeting Anopheles mosquitoes as malaria vectors. Conducted in collaboration with an international team of scientists from the University of Massachusetts at Amherst, the National Institute of Hygiene and Epidemiology in Hanoi, and the Naval Medical Research Unit TWO, this study could have life-saving applications. The findings were published in the Malaria Journal in January 2020.

The international team of scientists developed a controlled study in which an airborne insecticide, transfluthrin, was used to incapacitate or repel mosquitoes, specifically Anopheles dirus and Anopheles minimus – two species of mosquitoes that are the main malaria vectors in Vietnam.

The key to this study is transfluthrin – a synthetic insecticide and spatial repellent that evaporates into the air, but is fortunately of low toxicity to mammals. They found that burlap fabric that was impregnated with transfluthrin effectively increased mosquito knockdown and mortality, with best results at closer distances just a few meters away from the fabric.

Spatial repellents such as transfluthrin act on odour receptors in mosquitoes’ antennae to elicit changes in feeding behaviour, in contrast with traditional insecticides that rely on direct contact with mosquitoes to exert toxic effects. Spatial repellents essentially produce a barrier space between humans and the mosquitoes.

The findings of this study may go a long way in developing new malaria prevention methods, or improving current measures. Dr Ian Mendenhall, the lead of this study, Principal Research Scientist from the Emerging Infectious Disease (EID) programme at Duke-NUS, shared, “The results of our study are promising because it shows that spatial repellents can be a relatively inexpensive approach to minimise contact between humans and vectors, driving down transmission rates,” he said, adding that “there is potential to widely adapt these findings and implement treated bed nets and curtains into an integrated mosquito management programme that could help drive down malaria infections.”

Rather interestingly, the two species of mosquitoes exhibited different reactions to airborne transfluthrin exposure. An. minimus appeared to be more susceptible to knockdown and mortality, as compared to An. dirus. The research team recommends that future studies investigate these different responses to transfluthrin, as well as how transfluthrin may play a role in insecticide resistance and in disrupting mosquito-biting behaviours.

On the findings of this study, Professor Patrick Casey, Senior Vice Dean for Research at Duke-NUS, remarks: “The work being done in Southeast Asia bodes well to better understand disease hosts, such as the Anopheles dirus and Anopheles minimus mosquitoes, and how to counter them. Duke-NUS’ EID programme is building up much needed expertise in a world where infectious diseases threaten to disrupt and endanger communities and economies.” [APBN]