Mosquitoes bite some of us more than others, here’s why
Mosquitoes are known to find their desired “human snacks” using CO2 exhales, body heat and smell. However, some of us often complain about getting more than our fair share of bites. There are numerous theories as to why mosquitoes might prefer other people – blood type, blood sugar level, being a woman or a child, all without enough credible data.
Vosshall and Maria Elena De Obaldiaa former postdoc in the lab, decided to investigate the leading theory that explains the variable attractiveness of mosquitoes: individual odor variations associated with skin microbiota.
According to the study published in the article, “Differential mosquito attraction to humans is associated with skin-derived carboxylic acid levels.”
They recently showed that fatty acids released from the skin can create an intoxicating perfume that mosquitoes can’t resist. They published their results in Cell.
“There’s a very, very strong connection between high levels of fatty acids in your skin and mosquito magnets,” said Vosshall, Robin Chemers Neustein Professor at Rockefeller University and scientific director of the Howard Hughes Medical Institute.
In a three-year study, eight participants were asked to wear nylon stockings over their arms for six hours a day. They repeated this process for several days. Over the next several years, researchers tested nylons against each other in all possible pairings through a round robin-style “tournament”.
They used a two-choice olfactometer assay constructed by De Obaldia, which consisted of a Plexiglas chamber divided into two tubes, each ending in a box containing a sock. They placed Aedes Aegypti mosquitoes—the primary vector species for Zika, dengue, yellow fever, and chikungunya—in the main chamber and watched as the insects flew down tubes toward either the nylon or the other.
By far the most attractive target to Aedes aegypti was subject 33, which was four times more attractive to mosquitoes than the next most attractive study participant and an astonishing 100 times more attractive than the least attractive, subject 19.
In the experiments, the samples were not identified, so the experimenters did not know which participant had used which nylon. Still, they noticed that in any experiment involving subject 33, something unusual was going on, as insects flocked to that sample. “It would be obvious within seconds of starting the assay,” says De Obaldia. “That’s the kind of thing that really excites me as a scientist. This is something real. This is not splitting hairs. This is a huge impact.”
The researchers sorted the participants into high and low attractors and then asked what set them apart. They used chemical analysis techniques to identify 50 molecular compounds that were elevated in the sebum (the skin’s moisturizing barrier) of highly 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 in sebum, and the bacteria on our skin use them to produce the unique human body odor.
To confirm their findings, Vosshall’s team enrolled another 56 people in a validation study. Again, topic 33 was the most attractive and remained so over 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,” De Obaldia says. “A lot of things could have changed about the subject or their behavior during that time, but this was a very stable feature.”
Humans mainly produce two classes of odors, which mosquitoes detect with two different sets of olfactory receptors: Orco and IR receptors. To see if they could engineer mosquitoes that couldn’t detect humans, the researchers created mutants that lacked one or both of the receptors. The Orco mutants remained attracted to humans and could distinguish between mosquito magnets and shallow lures, while the IR mutants lost their attraction to humans to varying degrees but retained the ability to find us.
These were not the results the researchers were hoping for. “The goal was a mosquito that would lose all attraction to humans, or a mosquito that would have reduced attraction to everyone and couldn’t distinguish subject 19 from subject 33. That would be awesome,” says Vosshall, because it could lead to the development of more effective mosquito repellents. “And yet that wasn’t what we saw. It was frustrating.”
These results complement one of Vosshall’s recent studies, also published in Cell, which revealed redundancy in Aedes aegypti’s extremely complex olfactory system. It is a bug shelter where the female mosquito lives and reproduces. Without blood, he can do neither. That’s why “he has a back-up plan, a back-up plan, a back-up plan, and he’s attuned to the differences in the skin chemistry of the people he’s following,” says Vosshall.
The apparent unbreakability of the mosquito odor meter makes it difficult to imagine a future where we are not number one on the menu. But one possible way is to manipulate the skin’s microbiome. It is possible that applying the skin of an attractive person like subject 33 with sebum and skin bacteria from the skin of an unattractive person like subject 19 could produce a mosquito-repelling effect.
“We haven’t done that experiment,” Vosshall points out. “It’s a difficult experiment. But if it worked, you could imagine that if you put bacteria on the skin that could somehow change the way they interact with sebum, you could change someone through diet or microbiome therapy. Like subject 33 to subject 19. But it it’s all very speculative.”
He and his colleagues hope this paper will inspire researchers to test other mosquito species, including the Anopheles mosquito species that transmit malaria, Vosshall adds: “I think it would be really cool to find out if this is a universal effect.”
HT
Source: ANI