If you’ve always felt like you’re a mosquito magnet, scientists now have important evidence for you: Mosquitoes are more attracted to certain humans, according to a new study. A research team led by Leslie Vosshall, a Rockefeller University professor and director of her behavioral and neurogenetics lab, sought to identify why certain people seem to attract more mosquitoes than others. The results of the research were published in the journal Cell on October 18.
Over the course of the last three years, the researchers asked a group of 64 volunteers to wear nylon stockings on their arms for six hours a day for several days. Maria Elena De Obaldia, the first author of the study and a former postdoctoral fellow at Rockefeller University, built a “two-choice olfactometer assay”: an acrylic glass chamber into which the researchers placed two of the stockings. The study team then released yellow fever mosquitoes — scientifically called Aedes aegypti — into the chamber and noted which sock attracted them the most.
This test allowed the researchers to separate study participants into “mosquito magnets,” whose socks attracted a lot of mosquitoes, and “low attractors,” who didn’t seem as attractive to insects. The scientists examined the skin of the mosquito magnets and found 50 molecular compounds that were higher in these participants than in the others.
“We had no preconceived notions about what we would find,” Vosshall, who is also chief scientific officer of the Howard Hughes Medical Institute, told CNN. But one difference was particularly distinctive: Mosquito magnets have much higher rates of carboxylic acid in the skin than low attractors.
Carboxylic acids are found in sebum, the oily substance that creates a barrier and helps keep skin hydrated. Carboxylic acids are large molecules, Vosshall explained. “They’re not that smelly by themselves,” she said. But beneficial bacteria on the skin “chew these acids, which produce the characteristic human odor,” which may be what attracts mosquitoes, according to Vosshall.
The odor of skin secretions plays a role
One of the study participants, identified as Subject 33, was the center of attention for mosquitoes: the subject’s stockings were 100 times more attractive to mosquitoes than those of the rest of the participants.
And the level of human attraction appeared to remain fairly constant over time for the participants who were tracked over the three-year period, Vosshall said.
Subject 33, for example, “never stopped being the most attractive human being” to mosquitoes, which could be “bad news for those who are mosquito magnets.” When it comes to the Aedes aegypti mosquito, the females prefer to use human blood to fuel their egg production, speeding up their search for humans to hunt. And these mini-predators use a variety of mechanisms to identify and choose the humans they bite, Vosshall said.
Carboxylic acids are just one piece of the puzzle that explains how pesky insects choose their targets. Body heat and the carbon dioxide we release when we breathe are also a factor of attraction.
Scientists don’t yet know why carboxylic acids seem to attract mosquitoes so strongly, Vosshall said. But the next step could be to explore the effects of reducing carboxylic acids on the skin.
“You can’t completely remove natural moisturizers from your skin, that would be bad for your skin’s health.” However, Vosshall said dermatological products could minimize carboxylic acid levels and reduce mosquito bites.
“Each bite of these mosquitoes puts people in a dangerous situation for their health,” he said. “Aedes aegypti mosquitoes are contagious vectors for dengue, yellow fever and Zika. Those magnet people will be much more likely to get infected with those viruses.”
Mosquitoes evolved to hunt based on scent
Matthew DeGennaro, an associate professor at Florida International University who specializes in mosquito neurogenetics, told CNN that the study results help answer long-standing questions about what specific factors cause mosquitoes to choose some humans more. than others. He did not participate in the study.
“This study clearly shows that these acids are important,” he said. “Now the way mosquitoes perceive these carboxylic acids is interesting because these particular chemicals are really heavy, so they’re hard to smell from a distance.”
“It could be that these chemicals are altered by, say, the skin microbiome, and that causes a certain type of odour. Or it could be that other factors in the environment break down these chemicals a bit, so they’re easier for mosquitoes to detect.”
The results are also “a great example of how well insects can smell,” DeGennaro added. “This insect has evolved to hunt us.” For DeGennaro, the staying power of certain humans’ attractiveness is one of the most interesting aspects of the research.
“We didn’t know that there were very stable preferences of mosquitoes for certain people,” he said. “It might suggest that the skin microbiome is important, although they didn’t address that.”
Further research should explore the microbiome that exists on human skin to understand why mosquitoes are attracted to certain compounds over others, she said. And that could lead to better products to reduce mosquito bites and the spread of disease.
“I think if we understand why mosquitoes find a host, we can design new repellants that stop mosquitoes from detecting those chemicals,” DeGennaro said. “And this could be used to improve our current repellents.”
(With information from CNN in Spanish)