Why certain people are magnets for mosquitoes

A female mosquito will hunt down any member of the human by monitoring our CO2 exhalations, body heat, and body odour, so it is impossible to hide from her. But some of us are clearly "mosquito magnets" who get more bites than we should. Popular explanations for why someone might be a favoured snack include their blood type, blood sugar level, use of garlic or bananas, gender, and age. Leslie Vosshall, director of the Rockefeller Laboratory of Neurogenetics and Behavior, notes that there isn't much reliable information available for the majority of them.

This is the reason Vosshall and Maria Elena De Obaldia, a former postdoc in her lab, decided to investigate the top theory to account for variations in mosquito attraction: personal odour variations linked to skin microbiota. In a recent study, it was shown that the strong scent produced by skin-emanating fatty acids may be what repels mosquitoes. Their findings were published in Cell.

Vosshall, the Robin Chemers Neustein Professor at The Rockefeller University and the Chief Scientific Officer of the Howard Hughes Medical Institute, asserts that there is a "very, very strong association" between having a lot of these fatty acids on your skin and drawing mosquitoes to you.

Eight individuals were requested to wear nylon stockings over their forearms for six hours each day for the duration of the three-year trial. They went through this process several times. The nylons were pitted against one another in all conceivable pairings throughout the course of the following few years in a round-robin style "tournament." De Obaldia created a two-choice olfactometer assay for them, which consisted of a plexiglass chamber split into two tubes, each of which ended in a box holding a stocking. In the main chamber, they positioned Aedes Aegypti mosquitoes, which are the main carriers of Zika, dengue, yellow fever, and chikungunya. They watched as the insects flew down the tubes in either the direction of one nylon or the other.

Subject 33 was by far the most alluring target for Aedes aegypti, attracting the mosquitoes 100 times more than Subject 19, who was the least attractive research participant, and four times more than the next most alluring subject.

The trial samples were de-identified, so the researchers had no way of knowing which individual had donned which nylon. In any trial involving Subject 33, however, they would realise that something was off because insects would flock to that sample. De Obaldia claims that it would become clear shortly after the assay began. "As a scientist, it's the kind of stuff that really excites me. This is a genuine situation. This is not a case of nitpicking. The impact is significant."

The subjects were divided into high and low attractors, and the researchers then inquired as to what made each group unique. 50 molecular components that were higher in the sebum (a moisturising barrier on the skin) of the very attractive participants were found using chemical analysis techniques. This led them to the conclusion that mosquito magnets produced carboxylic acids at substantially higher amounts than the less attractive participants. Our distinct human body odour is created by bacteria on our skin using ingredients found in the sebum.

Vosshall's team recruited an additional 56 participants for a validation study to validate their findings. Subject 33 continued to be the most intriguing subject throughout time.

"We discovered that if they were a mosquito magnet, they remained a mosquito magnet," adds De Obaldia. "Some individuals were in the study for several years. Numerous aspects of the subject or their behaviours "might have altered throughout that time, yet this was a relatively stable quality of the person."

Mosquitoes have two distinct sets of olfactory receptors, known as Orco and IR receptors, which they use to detect primarily two groups of human scents. The researchers developed mutants lacking one or both of the receptors to explore if they might make mosquitoes that were unable to detect humans. While IR mutants lost their attraction to us to varying degrees but still had the ability to locate us, Orco mutants continued to be drawn to humans and were able to distinguish between mosquito magnets and low attractors.

The scientists had not anticipated these findings. "The ideal mosquito would have no attraction to humans, or would have a weaker attraction to everyone and be unable to distinguish between Subject 19 and Subject 33. That would be fantastic, "Because it might result in the creation of more potent insect repellents, claims Vosshall. "However, it was not what we observed. It was annoying."

These findings support a recent study by Vosshall that was also published in Cell and that demonstrated the redundancy of the extraordinarily intricate olfactory system of Aedes aegypti. The female mosquito depends on it as a backup to survive and procreate. She cannot perform either action without blood. Vosshall claims that as a result, "she has a backup plan, a backup plan, and a backup plan" and is aware of the variations in the skin chemistry of the targets she targets.

It is challenging to imagine a world in which humans are not the main course on the menu due to the mosquito scent tracker's seeming unbreakability. However, altering the microbiomes on our skin is one option. It's possible that applying sebum and skin bacteria from the skin of a low-appeal person, like Subject 19, to the skin of a high-appeal person, like Subject 33, could have the effect of masking mosquitoes.

Vosshall says, "We haven't tried that experiment." "That experiment is challenging. But if that were to be successful, you may think that you could change someone like Subject 33 into a Subject 19 by introducing bacteria through a nutritional or microbiome intervention that alters how they interact with sebum. But all of it is purely theoretical."

Vosshall continues, "She and her coworkers hope that this paper will motivate researchers to test other mosquito species, including in the genus Anopheles, which transmits malaria." "I think that figuring out whether this is a general effect would be really, really cool."