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Beyond Bed Nets: Study Tests New Way to Repel Mosquitoes

Jonathan Cox / Khmer Times Share:
An Anopheles mosquito enjoying a meal of blood from a human host. Jim Gathany

A new study suggests that “emanators” that slowly release chemical vapors over time could be an effective way to keep mosquitoes at bay, even when people cannot shelter under mosquito nets.
In response to the rising threat of mosquito-borne diseases like zika, dengue and malaria, the Cambodian government has advised people to sleep under bed nets. While these nets are effective at night, repelling mosquitoes during the day and evening is not so simple, especially for farmers or other people in rural Cambodia who spend most of their time outdoors. 
“Many cases [of mosquito-borne diseases] … may be acquired when people go to the forest for logging activities or when watching television before they go to bed, times and situations when bed nets make little difference,” the study said. 
Emanators – small plastic devices that diffuse a chemical vapor through to air to stun or kill mosquitoes – have been considered a possible solution. The study, published yesterday in the scientific journal Medical and Veterinary Entomology, tested how good emanators are at repelling mosquitoes outside during the day and evening. 
Researchers set up outdoor emanators in Pailin, Pursat and Koh Kong provinces and after counting a mind-numbing 29,255 mosquitoes, they found that the emanators in Pailin and Pursat cut mosquito landing rates by roughly 48 percent. 
Aside from stopping mosquitoes from landing, the emanators have the added benefit of being mobile.
“The whole point of them is that they can be taken to the forest,” said one of the study’s co-authors, Dr. Derek Charlwood. “People going [into the] forest, where the mosquitoes are, could hang them up around their camp at night and that would reduce their exposure.”
Emanators can also be set up in houses. This could help repel one of the most dangerous subspecies of mosquito in Cambodia, Anopheline dirus. It is one of the only species of mosquito that flies high enough to reach stilt houses and specifically targets human hosts – behavior that Dr. Charlwood said may be due to the fact that the species also feeds on monkeys living in trees. 
The chemical mosquito repellent tested by Dr. Charlwood and his colleagues for the study is called metofluthrin. Discovered by the Japanese company Sumitomo Chemical in 2005, it is a neurotoxin that can kill or stun mosquitoes without causing negative effects to human beings. 
Sumitomo’s metofluthrin emanator is a simple plastic mesh held inside plastic casing, and unlike other emanators, it does not require electricity. The mesh is impregnated with the chemical and stays effective up to four weeks after it is installed – much longer than the roughly 90-minute effectiveness of bug spray.
Though the emanators have benefits, the study’s authors said it is uncertain whether they will become a common sight in Cambodian villages just yet. 
“The recorded reduction in biting, although significant, may perhaps insufficiently reduce the annoyance of biting insects to convince the local population of its cost-effectiveness,” the study said.  
Dr. Charlwood said the emanators need to be improved. But with reports of more malaria strains developing resistance to some of the most commonly-used drugs, the study said Cambodia needs to find a way to stop or slow the spread of the virus soon. Bed nets, it said, are not enough.

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