The resultspublished Tuesday in the journal Cell, could lead to new products that may mask or alter certain human odors, making it harder for mosquitoes to find human blood and potentially curbing the spread of disease.
Mosquito-borne diseases affect about 700 million people a year, and experts expect that number to rise as global temperatures rise, said University of Washington professor and health expert Jeff Riffell. mosquitoes who did not participate in the research. A. aegypti mosquitoes are known to live in tropical or subtropical climates, but the insect is now breeding all year in the district and parts of California.
Just by breathing, we tell mosquitoes that we’re there, said Leslie Vosshall, scientific director of the Howard Hughes Medical Institute and principal investigator behind the new study. Female mosquitoes are designed to bite blood, because without it they won’t have enough protein to reproduce.
“Think of it like a big protein shake,” Vosshall said. “It’s a way for them, in one minute, to absorb the equivalent of 150 pounds of food and then use it to produce eggs.”
Scientists already knew that these mosquitoes had a preference for some humans over others, but the reason is not fully understood.
Experts have found that people seem to become more attractive to mosquitoes when they they are pregnant or after having a few beersprompting further research into whether mosquitoes can be attracted to certain smells.
Vosshall, whose lab is at Rockefeller University, investigated why some people seem to smell better of an A. aegypti mosquito that others.
Luckily, no one had to sit in a room full of mosquitoes to conduct this experiment. Instead, the researchers collected the natural scent of people’s skin by having them wear nylon stockings over their arms. They cut the stockings into two-inch pieces and placed two pieces of fabric behind two separate hatches in a clear plastic box where dozens of mosquitoes were flying. The researchers then opened the traps and the insects would choose to fly to the bait – the downs – behind the first or second door.
Vosshall said the researchers held a round robin and counted each time an insect was attracted to a particular sample, much like the points in a basketball game. One of the samples, described as being from “subject 33”, emerged as a favorite of the insects.
“Subject 33 has won a hundred games,” Vosshall said. “They were completely undefeated. Nobody beat them.
The study found that people like Subject 33, who have higher levels of compounds called carboxylic acids on their skin, are more likely to be “mosquito magnets,” Vosshall said.
All humans produce carboxylic acid through sebum, a waxy layer, on their skin. The sebum is then eaten up by the millions of beneficial microorganisms that colonize our skin to produce more carboxylic acid. In large amounts, the acid can produce an odor that smells like cheese or smelly feet, Vosshall said. This smell seems to attract female mosquitoes looking for human blood.
Notably, the nylon stockings used in the study didn’t really smell of sweat, she said. Mosquitoes are incredibly sensitive to human scent; and perfume or cologne can’t cover it. The experiment was conducted over three years, and the same people continued to call on the mosquitoes, regardless of what they ate that day or if they changed their shampoo, Vosshall said.
“If you’re a mosquito magnet today,” Vosshall said, “you’ll be a mosquito magnet three years from now.”
The study did not explain why some people have more carboxylic acids on their skin than others. But, Vosshall said the makeup of the skin microbiome is unique to each individual.
“Everyone has a completely unique village of bacteria living on their skin,” Vosshall said. “Some of the differences in mosquito magnetism that we see here may simply be the differences in the types of bacteria.”
LJ Zwiebel, a professor at Vanderbilt University who was not involved in the research, said that while carboxylic acids are clearly implicated in the study, there is no “single compound” that attracts mosquitoes. It’s probably a “cocktail” of different components that signals the mosquito to come in and bite, he said.
“The mosquito is a multimodal magnet that uses many different signals,” Zwiebel said. Carboxylic acids are “an important component but not the only one”.
For someone who doesn’t want to be bitten by mosquitoes, Zwiebel said his advice is to take a shower to reduce “all those juicy compounds” that are on your skin, especially around your feet, with its ” unique smells”.
Vosshall said that the The future lies in figuring out how to “manipulate” the odors that come from the skin and, potentially, the bacteria that live there. Scientists, for example, may be able to develop a probiotic skin cream that interferes with or reduces levels of certain by-products, which could make a person less attractive to mosquitoes.
“It’s only when you understand what makes people a mosquito magnet that you can start thinking about ways to stop it,” Vosshall said.