December 2, 2022
Mosquitoes

Mosquitoes

Researchers Learn Why Certain People Attract Mosquitoes More Than Others

The female mosquito will hunt down any person, although some of us experience significantly more bites than others. Our skin could hold the key to understanding why.

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 differences in mosquito attraction: personal odor 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 reported in Cell.

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

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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 several years in a round-robin type “tournament.”

De Obaldia created a two-choice olfactometer test 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 room, they positioned Aedes Aegypti mosquitoes, which are the principal 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 study involving Subject 33, however, they would realize that something was off because insects would flock to that sample. De Obaldia claims that it would become clear shortly after the test began. As a scientist, this is the kind of stuff that truly excites me. This is a genuine situation. This is not a case of nitpicking. It has a significant impact.

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 moisturizing barrier on the skin) of the very attractive individuals were found using chemical analysis techniques.

This led them to the conclusion that mosquito magnets generated carboxylic acids in substantially higher amounts than the less attractive participants. Our distinct human body odor 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.

“Some subjects were in the study for several years, and we saw that if they were a mosquito magnet, they remained a mosquito magnet,” says De Obaldia. “Many things could have changed about the subject or their behaviors over that time, but this was a very stable property 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 whether they might make mosquitoes that were unable to detect people. While IR mutants lost their attraction to us to varying degrees but still had the capacity 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 objective was to create a mosquito that would no longer be attracted to humans or a mosquito with a weaker attraction to everyone and the inability to distinguish between Subject 19 and Subject 33. That would be fantastic, adds Vosshall, as it would encourage the creation of more potent insecticides. “But we didn’t actually see that. It made me angry.”

These results complement one of Vosshall’s recent studies, also published in Cell, which revealed the redundancy of Aedes aegypti’s exquisitely complex olfactory system. It’s a failsafe that the female mosquito relies on to live and reproduce. Without blood, she can’t do either. That’s why “she has a backup plan and a backup plan and a backup plan and is tuned to these differences in the skin chemistry of the people she goes after,” Vosshall says.

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 likely 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, might have the effect of hiding mosquitoes.

“We haven’t done that experiment,” Vosshall notes. “That’s a hard experiment. But if that 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 how they interact with the sebum, then you could convert someone like Subject 33 into Subject 19. But that’s all very speculative.”

It’s impossible to imagine a world in which humans aren’t the most popular dish on the menu given the mosquito smell tracker’s seeming impenetrability. However, altering our skin’s microbiota is one option. It’s feasible to have a mosquito-masking effect by 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. (ANI)

Do You Attract Mosquitoes More Than Others? Here’s Why

 

Seen through mosquito netting, mosquitos feed on Robert Harrell at the University of Maryland Biotechnology Institute’s Insect Transformation Facility in Rockville, Md., on June 3, 2009.
Mosquitoes

 

Are you a “mosquito magnet?” Based on a study published Tuesday, there is real evidence that proves some people really do attract mosquitoes more than others — and it has to do with your smell.

What smell attracts mosquitoes?

In a paper published on Oct. 18 in the scientific journal Cell, researchers found that mosquitoes are drawn to certain body odors, which is why some people get a bit more than others.

Mosquitoes are enticed by people with high levels of carboxylic acids. Every person has unique levels of chemical compounds that create their individual scent. Those who produce high levels of carboxylic acids on their skin are the ones who attract mosquitoes.

“If you have high levels of this stuff on your skin, you’re going to be the one at the picnic getting all the bites,” said Leslie Vosshall, a neurobiologist at Rockefeller University in New York, per Scientific American.

Researchers also found that changes in grooming habits or diet did not impact an individual’s attractiveness to mosquitoes, meaning that the levels of these acids — and therefore attractiveness to mosquitoes — remained steady over time.

Scientists have theorized about why mosquitoes prefer certain individuals for years. Many believed odor played a role, but until this experiment, no one knew which smell was most popular among mosquitoes.

What happened in the study?

Researchers gathered 64 participants and asked them to wear nylon stockings on their arms for six hours. During this time, each individual’s scent profile was absorbed into the nylon.

“Those nylons would not have a smell to me or, I think, to anyone really,” said Maria Elena De Obaldia, lead author of this new study. However, the smell was certainly strong enough for the mosquitoes.

The stockings were put head to head in closed containers with dozens of mosquitoes to see which scent was most popular.

“They would basically swarm to the most attractive subjects,” De Obaldia said, according to The Associated Press. “It became very obvious right away.”

The experiment went on for months, and it was clear that some participants were far more attracted to mosquitoes than others. One subject received an attractiveness score “over 100 times greater” than the least favorite subjects.

Once enough evidence was gathered, researchers took a closer look at each subject’s scent profile and found a pattern — those with high levels of carboxylic acids were the most attractive to mosquitoes.

What does this mean for mosquito repellent?

DEET is the active ingredient used in many insect repellents. The chemical compound deters mosquitoes once they land. Mosquitoes can taste with their feet, so when they land and get a taste of DEET, they are driven away.

“Mosquitoes are repelled by its smell and by its taste,” Vosshall previously told NPR.

Although DEET was developed in the 1940s, it is still considered the most effective insect repellent today, with one major downside — it has to be reapplied often.

Researchers are hopeful that the new research will lead to a more state-of-the-art insect repellent that will protect even the biggest mosquito magnets in the future.

Why Do Some People Attract Mosquitoes More Than Others?

Mosquitoes (e.G., Aedes aegypti) are common vectors for many viruses that infect the human population, such as dengue, Zika, and yellow fever. A single female mosquito can bite multiple humans during her three-six weeks lifetime. Aedes aegypti is an efficient vector because it has a strong innate drive to hunt human hosts via sensory cues, such as body heat, exhaled carbon dioxide (CO2), and skin color.

Study: Differential mosquito attraction to humans is associated with skin-derived carboxylic acid levels. Image Credit: Fendizz / Shutterstock

Background

Although body heat and CO2 are common stimuli that indicate a living, warm-blooded animal, specific skin odor aids in identifying whether the target is non-human or human. In addition, although a large body of research has indicated that mosquitoes are more strongly attracted to some individuals than others, the underlying mechanism for this behavior is not yet clear.

Some non-scientific speculation associated with why some people attract mosquitoes more than others include the difference in blood type, pregnancy, malaria parasite infection, and beer consumption. Nevertheless, the most widely accepted explanation is differences in skin odor driven by an individual’s unique skin microbiota.

Human skin odor is a mixture of many organic compounds, the exact composition of which has not been extensively studied. Further, the extent of inter-individual variation in skin odor is yet to be analyzed thoroughly. Therefore, it is unknown which components are key in driving mosquito attraction to humans.

Depending on the exact composition and concentration of specific molecules, specific blends of odorants can be less or more attractive. For example, research has shown that the blend of ammonia and lactic acid strongly elicits mosquito attraction. Also, carboxylic acids augment mosquito attraction when combined with ammonia and lactic acid.

About the Study

In a new study published in the journal Cell, scientists evaluated the skin-derived compounds that distinguish between highly and weakly attractive humans. The mosquito sensory pathways required to determine such people were also analyzed. A two-choice behavioral assay was developed to test mosquito attraction with higher throughput. This allowed for frequent and repeated sampling of human subjects. Human skin odor samples from nylon stockings worn on the forearms were collected from 64 human subjects. After that, mosquitoes were studied to determine which nylon stockings were attractive to them.

Key Results

A cohort of weakly and highly attractive people to mosquitoes was discovered. It was also documented that the Orco (odorant receptor co-receptor) was not required to discriminate between them. Furthermore, the differential attractiveness of individuals to mosquitoes was found to be stable over many months and linked to the abundance of skin-associated carboxylic acids.

The highly attractive group produced more significant levels of three carboxylic acids, pentadecanoic, heptadecanoic, and nonadecanoic, and ten other unidentified compounds in the same chemical class. However, the specific blend of these chemicals differed among the highly attractive subjects. It was, therefore, concluded that there could be multiple reasons why an individual is highly attractive to mosquitoes. No specific chemical was noted to be produced in high quantities for less attractive subjects.

The attractiveness of an individual could depend on group settings as well; the “mosquito magnet” in a group could receive multiple bites while leaving the less attractive humans more or less untouched. It was proposed that exceptionally high or low attractiveness was a “fixed trait” that remains constant over several years. Research has also shown that identical twins are more similarly attractive to mosquitoes than fraternal twins, suggesting the presence of a genetic component.

It was observed that there was extensive redundancy in detecting human-derived skin odors. A possible mechanism of the ionotropic receptor (IR) could be its use of not one but three co-receptors for the odorant receptor (OR) system. The findings documented in this study show that mosquitoes do not distinguish between weakly and highly attractive humans using a single odor.

Concluding Remarks

The current study evaluated the association between the attractiveness of individual humans to mosquitoes and skin carboxylic acid abundance. However, causality could not be established as that would require confirming the necessity and sufficiency of specific chemicals for mosquito magnetics.

As mentioned above, human skin odor is a complex blend of several chemicals, and each requires its specialized detection method. This study mainly focussed on carboxylic acid groups, but it did not exhaustively document all human skin metabolites. Therefore, other types of compounds may influence mosquitoes’ differential attraction to humans. This issue was not addressed in this study.

The authors pointed out that carboxylic acids identified in the present study were not volatile, which raises the question about their function for differential mosquito attraction to humans across long distances. In the future, different analytical methods could be used to identify other compounds enriched on skin that attracts mosquitoes.

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