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Used socks reveal odor that attracts mosquitoes to malaria patients
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Used socks helped researchers identify compounds in the skin odor of malaria patients that make them more attractive to mosquitoes.
Previous research has shown that malaria parasites can alter patients’ breath to attract mosquitoes and drive disease transmission. In the new study, Ailie Robinson, BSc, MSc, PhD, medical entomologist and research fellow at the London School of Hygiene & Tropical Medicine, and colleagues explored the skin chemistry that attracts female Anopheles mosquitoes to the body odor of malaria patients.
They recruited asymptomatic Plasmodium-infected and -uninfected children aged 5 to 12 years in Western Kenya and collected foot odors from their socks for 20 hours on the first day of the study. Odors were collected from infected patients immediately after they were treated with the artemisinin-based combination therapy artemether-lumefantrine (AL), which is marketed in the United States as Coartem (Novartis).
Robinson and colleagues collected odors from socks 21 days later — after parasite clearance in infected patients was confirmed — and offered A. gambiae mosquitoes a choice between the two samples. They found that mosquitoes were more attracted to the foot odor of children who harbored Plasmodium than the foot odor of the same children collected 21 days later, after the parasites were cleared. Moreover, mosquitoes did not distinguish between the two odor samples of noninfected children, indicating the difference was not related to when the samples were taken, Robinson and colleagues said.
Experiments revealed that the skin aldehydes heptanal, octanal and nonanal were produced in greater amounts by infected children and detected by mosquito antennae.
“In behavioral experiments, we demonstrated that these, and other, Plasmodium-induced aldehydes enhanced the attractiveness of a synthetic odor blend mimicking ‘healthy’ human odor,” Robinson and colleagues wrote. “Heptanal alone increased the attractiveness of ‘parasite-free’ natural human odor. Should the increased production of these aldehydes by Plasmodium-infected humans lead to increased mosquito biting in a natural setting, this would likely affect the transmission of malaria.”
They said their findings have “far-reaching” implications, including potentially offering a new way to diagnose malaria.
“We better understand parasite-vector-host transmission events and their overdispersed nature in human populations,” they wrote. “These compounds may permit further improvement of already highly functional lures for trapping malaria mosquitoes or even serve as biomarkers for malaria, providing a basis for novel and noninvasive diagnostic tools.” – by Gerard Gallagher
Disclosures: Robinson and several other authors report being inventors on a patent application filed with the United Kingdom Intellectual Property Office.
Perspective
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Several studies over the past 5 to 10 years hint that malaria-transmitting mosquitoes are more attracted to hosts with Plasmodium infections. This discovery has led to the hypothesis that Plasmodium infection changes the odor of its host to increase transmission. In the study by Robinson and colleagues, the authors provide new, independent evidence that mosquitoes are more attracted to the smell of children with Plasmodium infection. In addition, they find some odorants that are both sensed by and attractive to mosquitoes. There are some limitations to this study, because children were treated with antimalarials at the start of a 20-hour odor collection, and so some parasite-generated odors could have been missed. In addition, only the children with Plasmodium infection received antimalarials, for understandable reasons, and this could have changed the odor profiles. Understanding where these Plasmodium-associated odors come from will be an exciting area for research and may lead to improved odor-baited mosquito traps.
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