Genetic Tweak Gave Mosquitoes a Nose for Human Blood

What gives mosquitoes a taste for human blood? It turns out that a small genetic tweak is responsible. Scientists are taking a closer look at the genetics of the mosquitoes that can carry yellow fever in order to better learn how best to prevent the spread of this disease.

"The more we know about the genes and compounds that help mosquitoes target us, the better chance we have of manipulating their response to our odor," said Carolyn "Lindy" McBride, one of the researchers, in a news release.

In order to examine which compounds triggered the mosquitoes-and what genetics were involved-the scientists conducted a three-part series of experiments with the yellow fever mosquito. The scientists placed forest and domestic mosquitoes in a large cage and then allowed them to bite either a guinea pig or a researcher's arm. Then, the mosquitoes chose between streams of air that had passed over a guinea pig or human arm. Finally, the mosquitoes chose between the scent of nylon sleeves that had been in contact with a human, or a guinea pig.

Surprisingly, in all three cases the domestic form of the yellow fever mosquito seemed to prefer the human scent. The forest form, in contrast, primarily chose the guinea pig.

The scientists then investigated a bit further by breeding the two mosquitoes and then looking at the genetics of these mosquito hybrids. In the end, they found 14 genes that differed between human- and guinea pig-preferring hybrids. Two of them were the deodorant receptors Or4 and Or103. The scientists then followed up on Or4 by implanting the gene into fruit-fly neurons. In the end, they found that the neurons exhibited a burst of activity when exposed to sulcatone, but no change when exposed to guinea pig odors.

The findings reveal a bit more about what causes mosquitoes to target humans. This, in turn, may allow researchers to better develop methods to deter mosquitoes and, in turn, prevent the spread of yellow fever.

The findings are published in the journal Nature.