For millions of people around the world, mosquitoes are not just annoying; they’re vectors of deadly disease. More than 214 million people were infected with malaria in 2015 alone. Public health experts are doing all they can to eradicate the disease, but the tiny mosquito has proved a formidable adversary. In recent years, mosquitoes have even begun to develop a resistance to pesticide. Now, one team of researchers has made a strange discovery with a lot of potential: malaria-carrying mosquitoes stay away from chickens, which might make the birds (or even just their odor) an effective repellent. The research was published in the Malaria Journal.
Nearly 90 percent of new malaria cases occur in sub-Saharan Africa, where the mosquito Anopheles arabiensis plagues people and livestock. So researchers at the Swedish University of Agricultural Sciences and Addis Ababa University decided to monitor the mosquitoes’ behavior to find out how the pests selected their hosts.
The team set up a number of experiments in the lab, outside, and in people’s homes in the Ethiopian villages of Wama Kusaye, Baka-Boro, and Machara. Villagers in these areas commonly share their living quarters with their sheep, goats, and cattle, so the mosquitoes have the same dining options indoors and out. The researchers collected mosquitoes from homes and open spaces around the villages, then analyzed the blood in the mosquitoes’ guts to find out what they’d been eating.
The scientists then collected samples of hair, wool, or feathers from animals in Wama Kusaye. The samples were shipped to a lab, where their headspace—that is, the composition of the odors surrounding each one—was analyzed.
Back in Wama Kusaye, the team recruited 11 volunteers. Each night for 11 nights, the volunteers slept under mosquito nets. At the foot of each bed, the researchers set up a mosquito trap infused with the odor of sheep, goats, cattle, or chickens. As a control group, they also set up a trap beside a live chicken inside a mosquito-proof cage.
The results were quite interesting. Analysis of the mosquitoes’ stomach contents showed that their dining preferences depended on the setting. Indoors, humans were their favorite meal, but al fresco meals were evenly (and seemingly randomly) divided among cattle, sheep, and goats. Chicken, on the other hand, was off the menu. Not only did the mosquitoes opt not to feed on the birds, but they actively avoided them. Bed traps baited with the smell of chicken feathers were far, far emptier than the ones that smelled like other animals, and the same was true for the trap set up beside the live chicken.
Why would mosquitoes avoid feeding on, or even approaching, chickens?
The researchers have a few theories. It might be that chicken blood is less appealing. It could also be that their feathers are better than wool or hair at keeping nosy bugs out. Analysis of their odor revealed the presence of two compounds that have previously been found in people who are “non-attractive” to mosquitoes, as well as two other compounds that are well known as natural insect repellents.
Then there’s the fact that, unlike cattle, sheep, goats, or people, chickens eat bugs, and they’re good at it. Mosquitoes may have learned that it’s in their best interest to avoid them.
One way or another, the researchers say, chickens may be the next big thing in malaria prevention. They’re already working on feather-inspired repellents and urge their colleagues to consider doing the same. “With the increasing reports on insecticide resistance among disease vectors,” they write, “it is incumbent on the international malaria community to embrace these novel control methods and products.”
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