Scientists discover why some people are mosquito magnets

A scientific study recently demonstrated that fatty acids emanating from the skin can create a heady scent that mosquitoes cannot resist.

It can be impossible to hide from a female mosquito – she will stalk any member of the human species by tracking our CO2 exhalations, body heat and body odor. However, some of us are distinct “mosquito magnets” who receive more than their fair share of bites. There are many popular theories as to why someone might be a favorite snack, including blood type, blood sugar level, garlic or banana consumption, being female, and being a kid. Yet there is little credible data to support most of these theories, says Leslie Vosshall, head of the Neurogenetics and Behavior Laboratory at Rockefeller University.

This is why Vosshall and Maria Elena De Obaldia, a former post-doctoral researcher in her lab, set out to study the main theory explaining the variable attractiveness of mosquitoes: individual odor variations linked to skin microbiota. Through a study, they recently demonstrated that fatty acids emanating from the skin can create a powerful scent that mosquitoes cannot resist. They published their results in the journal Cell October 18.

“There’s a very, very strong association between having high amounts of these fatty acids on your skin and being a mosquito magnet,” says Vosshall, Professor Robin Chemers Neustein at Rockefeller University and Chief Scientific Officer. from the Howard Hughes Medical Institute.

Researcher on female Aedes aegypti mosquito bites

A female Aedes aegypti mosquito bites a Rockefeller University researcher. 1 credit

A tournament no one wants to win

In the three-year study, eight participants were asked to wear nylon stockings over their forearms for six hours a day. This process was repeated over several days. Over the next few years, investigators tested the nylons against each other in all possible pairings in a round-robin style “tournament”. They used a two-choice olfactometric test that De Obaldia constructed, consisting of a Plexiglas chamber divided into two tubes, each ending in a box containing a stocking. They placed Temples of the Egyptians mosquitoes – the main vector species for Zika, dengue, yellow fever and chikungunya – in the main bedroom and watched as the insects flew through the tubes to one nylon or the other.

By far the most attractive target for Temples of the Egyptians was Subject 33, who was four times more attractive to mosquitoes than the next most attractive study participant, and 100 times more attractive than the least attractive, Subject 19.

Trial samples were anonymized, so experimenters did not know which participant wore which nylon. Yet they would notice that something unusual was brewing in any trial involving Subject 33, as the insects would swarm towards this sample. “It would be obvious a few seconds after the start of the test,” says De Obaldia. “That’s the kind of thing that really excites me as a scientist. It’s something real. It’s not splitting hairs. It’s a huge effect.

The participants were sorted into high and low attractors, then the scientists set out to determine what made them different. They used chemical analysis techniques to identify 50 molecular compounds high in the sebum (a moisture barrier on the skin) of the most attractive participants. From there, they found that the mosquito magnets produced carboxylic acids at much higher levels than the less attractive volunteers. These substances are found in sebum and are used by bacteria in our skin to produce our unique human body odor.

To confirm their findings, Vosshall’s team recruited 56 other people for a validation study. Again, Subject 33 was the most alluring and remained so over time.

“Some subjects had been in the study for several years, and we saw that if they were a mosquito magnet, they remained a mosquito magnet,” says De Obaldia. “A lot could have changed about the subject or his behaviors during this time, but it was a very stable property of the person.”

Even knockouts find us

Humans mainly produce two classes of odors that mosquitoes detect with two different sets of odor receptors: Orco and IR receptors. To see if they could engineer mosquitoes that couldn’t spot humans, the researchers created mutants that were missing one or both receptors. The Orco mutants remained attracted to humans and were able to distinguish between mosquito magnets and weak attractors, while the IR mutants lost their attraction to humans to a varying degree, but retained the ability to find us. .

These are not the results the scientists were hoping for. “The goal was a mosquito that lost all attraction to people, or a mosquito that had a weakened attraction to everyone and couldn’t discriminate Subject 19 from Subject 33. That would be great,” Vosshall says, because it could lead to the development of more effective mosquito repellents. “And yet, that is not what we have seen. It was frustrating.

These results complete one of the Vosshall’s recent studiesalso published in Cellwhich revealed the redundancy of Aedes aegypti extremely complex olfactory system. It is a fail-safe that the female mosquito relies on to live and reproduce. Without blood, she can’t do either. That’s why “she has a back-up plan and a back-up plan and a back-up plan and is attuned to those differences in the skin chemistry of the people she’s pursuing,” Vosshall says.

The Mosquito Scent Tracker’s apparent unbreakability makes it hard to envision a future where we aren’t the number one meal on the menu. But one potential lead is to manipulate our skin microbiomes. It is possible that painting the skin of a high-attractive person like Subject 33 with sebum and skin bacteria from the skin of a low-attractive person like Subject 19 could produce a mosquito masking effect.

“We haven’t had that experience,” Vosshall notes. “It’s a difficult experience. But if it were to work, then you could imagine that by having a dietary or microbiome intervention where you put bacteria on the skin that are able to somehow change the way they interact with sebum, then you could convert someone like Subject 33 to Subject 19. But this is all very speculative.

She and her colleagues hope this article will inspire researchers to test other species of mosquitoes, including the genus. Anophelesthat spreads malaria, adds Vosshall: “I think it would be really, really cool to know if it’s a universal effect.”

Reference: “The differential attraction of mosquitoes to humans is associated with skin-derived carboxylic acids.[{” attribute=””>acid levels” by Maria Elena De Obaldia, Takeshi Morita, Laura C. Dedmon, Daniel J. Boehmler, Caroline S. Jiang, Emely V. Zeledon, Justin R. Cross and Leslie B. Vosshall, 18 October 2022, Cell.
DOI: 10.1016/j.cell.2022.09.034

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