If you always suspected it might be a mosquito magnet, scientists now have evidence to show you: Mosquitoes are actually more attracted to certain humans than others, according to a new study.
A research team led by Leslie Vosshall, a professor at Rockefeller University and head of the neurogenetics and behavior lab, sought to identify why certain people seem to attract more mosquitoes than others. The research results were published in the journal Cell on Tuesday (18).
Over 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, first author of the study and a former postdoctoral fellow at Rockefeller University, constructed a “two-choice olfactometer assay” – an acrylic glass chamber in which the researchers place two of the socks.
The study team then released yellow fever mosquitoes, scientifically called Aedes aegypti, into the chamber and observed which sock attracted the most insects.
This test allowed the researchers to separate study participants into “fly magnets,” whose socks attracted lots of mosquitoes, and “low attractors,” which didn’t look as attractive to the insects. Scientists examined the skin of those who were the mosquito’s 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,” said Vosshall, who is also the scientific director of the Howard Hughes Medical Institute. But one difference was particularly distinct: those that were the mosquito magnets had much higher rates of carboxylic acid in their skin than the low attractors.
Carboxylic acids are found in sebum, the oily substance that creates a barrier and helps keep your skin hydrated.
Carboxylic acids are large molecules, explained Vosshall. They “are not so smelly on their own,” she said. But the beneficial bacteria in the skin “chew these acids, which produce the characteristic human smell” — which may be what attracts mosquitoes, according to Vosshall.
The odor of skin secretions plays a role
One of the participants, identified only as Subject 33, was the mosquito champion: the subject’s socks were 100 times more attractive to mosquitoes than the least attractive participants.
And the humans’ level of attraction appeared to remain fairly constant over time for the participants who were monitored over the three-year period, Vosshall said.
Subject 33, for example, “has never taken a day off to be the most attractive human,” which might be “bad news for mosquito magnets.”
When it comes to Aedes aegypti, female mosquitoes prefer to use human blood to fuel their egg production, giving urgency to the search for humans to feed on. And these minipredators use a variety of mechanisms to identify and choose the humans they bite, Vosshall said.
Carboxylic acids are just one piece of the puzzle to explain how pesky insects can choose their targets. Body heat and the carbon dioxide we release when we breathe also attract mosquitoes to humans.
Scientists still don’t know why carboxylic acids seem to attract mosquitoes so strongly, Vosshall said. But the next step may 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,” she said. However, Vosshall said that dermatological products can minimize carboxylic acid levels and reduce mosquito bites.
“Each bite from these mosquitoes puts people in danger to public health,” she said. “Aedes aegypti mosquitoes are vectors of dengue, yellow fever and zika. These people who are magnets will be much more likely to be infected with the viruses.”
Mosquitoes evolved to hunt by scent
Matthew DeGennaro, an associate professor at Florida International University who specializes in mosquito neurogenetics, said the study results help answer long-standing questions about what specific factors make mosquitoes love some humans more than others. He did not participate in the study.
“This study clearly shows that these acids are important,” he said. “Now how mosquitoes perceive these carboxylic acids is interesting because these chemicals in particular are very heavy, so they are difficult to smell from a distance.”
“It could be that these chemicals are being altered by, say, the skin microbiome, and that causes a certain type of odor plume. Or it could be that other factors in the environment break down these chemicals a little bit so they are easier for mosquitoes to detect.”
The results are also “a great example of how good insects are to smell,” added DeGennaro. “This insect evolved to hunt us.”
For DeGennaro, the staying power of the attractiveness of certain humans is one of the most interesting aspects of the research.
“We didn’t know there were very stable mosquito preferences for certain people,” he said. “It might suggest that the skin microbiome is important, although they haven’t addressed that.”
More research should explore the microbiome that lives on human skin to understand why mosquitoes are attracted to certain compounds over others, he 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 repellents that will prevent mosquitoes from detecting these chemicals,” DeGennaro said. “And that can be used to improve our current repellents.”
Source: CNN Brasil
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