In lab tests, insects carrying disease home in on sweat-soaked stockings
The notoriously crafty parasite that causes malaria may have yet another trick up its sleeve scientists have learned: It makes mosquitoes that carry it more attracted to human body odor, a new study suggests. Compared with noninfected mosquitoes, those carrying Plasmodium falciparum, the most dangerous of the parasites that carry malaria,visited a fabric covered with a person’s sweat far more frequently, researchers report May 15 in PLOS ONE.
Hundreds of millions of people have malaria, and more than 500,000 die of it each year. Plasmodium’s ability to manipulate its hosts could help explain its ability to infect so many people. Researchers have found that infected mosquitoes take longer blood meals than noninfected ones, increasing the odds that the parasite will be passed on.
Since mosquitoes find their prey using odor, scientists have wondered whether the parasite affects its host’s sense of smell. A 2007 study found that a species of Plasmodium parasite that causes malaria in rodents can alter mosquitoes’ olfactory proteins.
To study how the parasite affects mosquitoes’ attraction to people, a team led by Renate Smallegange, then of Wageningen University and Research Center in the Netherlands, collected foot sweat from a volunteer who wore nylon stockings for 20 hours. Then her team put the odor-laced fabric in a cage with two groups of Anopheles gambiae, mosquitoes that transmit the malaria parasite to people. One group was infected with Plasmodium falciparum; the other wasn’t.
Infected mosquitoes landed on the fabric three times as frequently as did noninfected mosquitoes, the researchers found.
“It's a very interesting, although somewhat preliminary, result,” says Michael Riehle, an entomologist at the University of Arizona in Tucson. He notes that the experiment used only 176 mosquitoes and just one person’s sweat.
The researchers don’t know how the parasite manipulates mosquitoes’ sense of smell. It’s also unclear which component of human odor is the most attractive to the mosquitoes. That information could help researchers develop traps to catch infected mosquitoes, the researchers say.
“We're at the tip of the iceberg, really, of understanding all the strategies the parasite is using in the mosquitoes,” says parasitologist Hilary Hurd of Keele University in England, who collaborates with some of the study’s authors. “That's remarkable, given that this is a single-celled organism we're talking about.”
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