If you're one of those people who mosquitoes just can't seem to resist, you can blame your genes, according to new research.
Previous studies have already found that different people naturally emit different odors that either attract or repel the insects, though it wasn't clear what caused these odors to differ from person to person: was it diet, or maybe body mass, or something else entirely? But a new pilot study from the London School of Hygiene & Tropical Medicine has found that genetics play a big factor in determining what kind of odor one's body gives off.
"The majority of what causes the level of attractiveness is down to genetics," James Logan, senior author on the study, which was published today in PLOS ONE, told me over the phone. "We know from previous studies that body odor is what mosquitoes use to find us and we know that difference in body odor causes different responses. What this study has done is taken that one step further to show that mosquitoes are picking up on odors that are controlled by genes, we just don't know which ones yet."
Logan and his team used sets of twins (some identical and some non-identical) to test out how much genes play a role in the body odors mosquitoes detect. The degree to which genes influence something is called heritability, and is measured on a scale from 0.0 to 1.0. In this study, twins would stick their hands into a y-shaped tube with another stimulus in the other side (either their twin, or empty air). Mosquitoes would then be released into the tube and counted to see how many flew towards a stimulus and how close they got.
"Identical twins are identical in their genetics. Non-identical twins differ in their genetics," Logan told me. "We can determine whether what we're seeing is controlled genetically by comparing the correlation between identical twins versus the correlation between non-identical twins."
In other words: imagine multiple sets of twins, some identical and some non-identical. If all the identical twins have the same effect on mosquitoes as their sibling (attraction or repulsion) but the non-identical twins differ from their sibling (one is attractive and the other repellent), it indicates that genes probably play a role.
The researchers found that the heritability of being attractive or repellent to mosquitoes was quite high, at 0.83. For context, research has shown height has a heritability factor of around 0.8 while IQ is somewhere between 0.5 and 0.8.
Though the pilot study used a relatively small sample size—they looked at 37 sets of twins—Logan said the high heritability rate is strong evidence that genes are playing a role in whether or not we smell tasty to mosquitoes.
So what does all this matter? Well, if researchers are able to identify the gene that turns on or off the repellent odor factories in a human body, they might be able to find ways to do that chemically. They could potentially create oral medications to make someone naturally repellent to mosquitoes, reducing the need for topical repellents and decreasing the risk of contracting illnesses mosquitoes carry, such as malaria and West Nile virus.
But first, Logan wants to do more research on the heritability in other populations, particularly in sub-Saharan Africa where the risk of certain mosquito-transmitted diseases is much higher.
"We could also potentially one day be able to identify members in a population that are most at risk of being bitten by mosquitoes and therefore most at risk of getting diseases like malaria or dengue fever," Logan said. "You could screen populations and then target your control to those individuals. It would also help with mathematical modeling of diseases because in a lot of models we assume that everybody gets bitten the same amount, but we know that's not the case."