Are you a human mosquito magnet? Your genes may be to blame, according to a study of twins that suggests your DNA is the main factor that makes some people much more appetizing to the pesky insects. The good news is that identifying the genes involved could help scientists devise ever more effective mosquito repellents.
An estimated 20 percent of people are especially attractive to mosquitoes. Puzzled scientists have explored many reasons why mosquitoes seem to prefer some people to others. Possibilities include a person's blood type, metabolism, exercise levels and even clothing color. Previous studies have even shown that Anopheles gambiae, a malaria-carrying scourge in Africa, is more attracted to pregnant women. Diet is another oft-cited culprit, but no solid link between certain foods and mosquito bites has been shown—despite the persistent but unproven claims that intake of garlic or beer will repel or attract the insects.
One thing science can agree on is that body odor seems to play a significant role. “The mosquito's sense of smell is the primary method used to select which human to feed on,” says James Logan of the London School of Hygiene & Tropical Medicine. “There is an enormous amount of data to support the fact that how attractive you are to mosquitoes is determined by body odor.” Now, by studying human twins, Logan and colleagues have found that the specific body odors that affect mosquitoes appear to have a genetic basis.
His team conducted experiments with sets of twin sisters who volunteered to be mosquito bait for the betterment of science—18 pairs of identical twins and 19 pairs of non-identical twins. Non-identical, or fraternal, twins share far fewer genes than identical twin pairs. To test their mosquito-attracting mojo, the twins each placed a hand into one branch of a Y-shaped tube. Then dengue mosquitoes (Aedes aegypti) were released into the third branch, where they could sense the human odors and fly down to bite whichever twin they found most attractive.
While the identical twins proved equally attractive to mosquitoes, some of the non-identical twins were far less likely to be bitten than their siblings. This matches previous work showing that identical twins are more likely to have the same body odor than fraternal twins, Logan says. According to their tests, the measured level of heritability for this trait—the amount of total variability in body odor that can be attributed to genetics—was quite high. The results suggest that genes may play as big a role in determining whether our smell attracts mosquitoes as they do in regulating our height or IQ. Other possible factors to account for mosquito attractiveness, including diet and cleanliness, were largely controlled for during the study.
The team's findings, published today in PLOS ONE, could prove a valuable weapon in the fight against these pests and the many diseases they transmit. Current repellents such as DEET aren't foolproof, and some mosquitoes can become immune to DEET in just a few hours.
Finding the genes that govern certain body odors may help scientists develop more targeted types of mosquito repellants, and the authors have identified one promising place to search. The major histocompatibility complex (MHC) genes are believed to control odor cues associated with genetic similarity—perhaps to help avoid inbreeding by deterring humans from being attracted to a close relative. Those same genes may somehow trigger odors that either attract or repel mosquitoes, the authors theorize.
“Once we identify the genes involved, we may be able to screen populations to better predict the likely level of risk of being bitten, which is directly correlated to transmission of diseases like malaria and dengue," says Logan. If the genes are linked to a repellent odor, "we may also be able to develop a drug which would up-regulate the production of natural repellents by the skin and therefore minimize the need for topical repellents.”