Why Do Mosquitoes Like To Bite You Best? It's In Your Genes
A study that asked a few dozen pairs of twins to brave a swarm of hungry mosquitoes has revealed another clue to the cluster of reasons the insects are more attracted to some people than others: Genes matter.
"Twins that were identical were very similar in their level of attractiveness to mosquitoes, and twins that were [not identical] were very different in their level of attractiveness," says James Logan, a medical entomologist at the London School of Hygiene & Tropical Medicine who led the study. "So it suggests that the trait for being attractive or unattractive to mosquitoes is genetically controlled."
It's long been known that female mosquitoes, which need the proteins in a blood meal to make their eggs, are more drawn to certain people than others, and that various factors are involved.
Women who are pregnant seem to attract the insects more than women who aren't, for example, and people infected with the malaria parasite seem to be most attractive during the period when the parasite is most transmissible.
In their own previous research, Logan and his colleagues found that people who are bitten less frequently seem to "smell differently to mosquitoes." It's almost as if they produce a natural repellent, he says.
The most recent study, published Wednesday in the journal PLOS ONE, indicates that there are likely specific genes behind those differences in people — genes that affect the way each person smells to the insects.
To figure that out, the researchers brought 18 pairs of identical twins and 19 pairs of fraternal twins into the lab. Each person stuck a hand in one of the short arms of a Y-shaped plexiglass tube, as air was blown past the hand, toward 20 female Aedes aegypti mosquitoes clustered at the long end of the Y. Once released, the insects could choose between the twins — to fly upwind, along either side of the Y, presumably following the odor of the person they were most attracted to. (The scientists used a new batch of hungry mosquitoes in each trial, and also compared the results to trials that involved "clean air" and nobody's hand.)
There was essentially no difference in the mosquitoes' response to genetically identical twins, the scientists found, but quite a bit of difference in their response to fraternal twins, who are as genetically different from each other as any other pair of siblings. Logan now wants to try to identify which genes exactly influence attractiveness.
"If we could work out which genes are involved, we could develop new repellents," Logan says — which could be much more than a boon to backyard barbeques. Mosquitoes spread lots of terrible diseases.
"The mosquito tested here, Aedes aegypti, is the main transmitter of the yellow fever virus, and the dengue virus, and some other infectious agents," says Richard Pollack, a public health entomologist at the Harvard School of Public Health. "So the more we learn about what causes a mosquito to find a person, the better we'll be able to design better strategies to protect people."
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Transcript
DAVID GREENE, HOST:
OK, spring just got here. But for many people, it's already time to start thinking about summer, soaking in the sunshine, maybe trips to the beach, barbecues and in many parts of the country, mosquitoes. You feeling itchy yet? Here's NPR health correspondent Rob Stein with some new research on those little buggers.
ROB STEIN, BYLINE: It's annoying enough when mosquitoes start buzzing around your ears, but it's downright crazy-making when they start biting you and nobody else around you. Ever wondered, why? Well, James Logan at the London School of Hygiene and Tropical Medicine has, too.
JAMES LOGAN: We have sort of anecdotal evidence from people that you know members of their family might get bitten more than others. And that led us to believe that there might be some sort of hereditary component. So there might be a genetic link with how attractive you are to mosquitoes.
STEIN: To try to find out, Logan and his colleagues brought 37 pairs of twins into the lab to do a series of experiments to see if there was any difference between the identical twins, who have exactly the same genes, and non-identical twins, who have different genes, in terms of being mosquito magnets or not.
LOGAN: In one of the experiments, we would have one twin's hand in one side and the other twin's hand in the other side and we could measure whether the mosquitoes flew to one twin or the other.
STEIN: And they report what they found in this week's issue of the journal Plos One.
LOGAN: The attractiveness of the identical twins was very similar to each other and much greater than when we looked at non-identical twins. So in the non-identical twin case, we find that one twin was usually more attractive than the other, which suggests that the genes are controlling certainly a significant proportion of how attractive you are to mosquitoes.
STEIN: The next thing Logan wants to do is try to identify which genes exactly do this and how. He hopes that will lead to better ways to keep mosquitoes away.
LOGAN: What we might also be able to do further down the line is possibly develop a drug that you could take that would cause the body to upregulate the production of natural repellents and therefore minimize the need for putting topical repellents on the skin.
STEIN: That would be a huge development and not just for backyard barbecues. Richard Pollack is a public health entomologist at Harvard. He says mosquitoes spread lots of terrible diseases.
RICHARD POLLACK: The mosquito tested here, Aedes aegypti, the yellow fever mosquito, is the main transmitter of the yellow fever virus and the dengue viruses and yet some other infectious agents. So the more we learn about what causes a mosquito to find a person, the better we'll be able to design better strategies to protect people.
STEIN: But Logan and Pollack agree that's a ways off. So for now, we're stuck slathering on the Deet, wearing long-sleeved shirts and pants and running back inside when we just can't take it anymore. Rob Stein, NPR News. Transcript provided by NPR, Copyright NPR.
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