Oo-ooh, that smell.

Growing up in a region of the States where mosquitoes grew to monstrous proportions, forcing us to sweat around the campfire in skin-encasing pants and long-sleeved shirts, worrying if we’d all spontaneously combust due to the cloud of DEET forming a force-field around us, I think I’ve heard all derivations of methods to keep mosquitoes away and why they’re attracted to people – some more than others. For me and for most of us living in industrialized countries, finding ways to repel mosquitoes is mostly just about nuisance. We want to avoid those irritating itchy bumps and sleepless nights from that one damn mosquito that got trapped in the bedroom with us. However, for hundreds of millions of people living in sub-Saharan Africa, South America, and Southeast Asia, repelling mosquitoes is really a life-or-death battle.

The reason we in the States and other industrialized nations don’t have to worry about anything more than a mosquito bite (and the occasional West Nile virus scare) is because the mosquito species (Anopheles gambiae, for the Latin-proficient) that transmits the most fatal malaria parasite (another tongue-twister: Plasmodium falciparum) was successfully eradicated from these regions. In third-world countries, the mosquitoes still wreak havoc on the population. Of course, the hot and humid climate is perfect for these little pests. But the problem is much bigger: these are poor, undeveloped nations without the infrastructure or financial resources to implement large-scale eradication procedures. There have been great successes with insecticide-treated bed nets, but obviously a lot more work needs to be done, since 1-3 million people still die from malaria every year, making it one of the top three infectious disease killers (the other two being HIV-AIDS and tuberculosis).

Fortunately, scientists are on the case to figure out what attracts mosquitoes to humans. Even better, they know something more than what we grew up hearing: “you’re just not sweet enough,” or “just stop breathing and they won’t bother you.” Actually, mosquitoes have special odorant receptors in their neurons that let them “smell” different chemicals. That’s right, even though mosquitoes don’t have noses, they can smell! There are many different types of these odorant receptors that allow the mosquitoes to detect different chemicals – very similar to how humans can detect different odors (Su C et al. Cell 2009;139(1):45-59). A fascinating article was just published in the journal Nature, in which the authors wanted to know exactly which receptors were responsible for detecting human odors – no, not the odors you and I can detect on a crowded subway, but the chemicals we emit just by being human (Carey AF, et al. Nature 2010;464:66-71). The researchers did something really tricky: they knew the gene for each individual receptor. They also had mutant fruit flies that were missing their odorant receptors. The scientists could insert the mosquito receptor into a fruit fly neuron! Why is this so cool, other than just the simple fact that they could technically do this? Because they could put one receptor into one neuron, without all the other receptors around, and they could tell exactly what each receptor could respond to. In other words, they have a neuron with receptor A, and another with receptor B. They expose these neurons to different chemicals, some of which are found in human odors. If neuron A responds to a chemical, but not neuron B, the scientists would know that receptor A allows the mosquito to recognize this chemical. Some chemicals activated just one receptor, while some chemicals activated several; some receptors were activated by a small range of chemicals, while others by a large range (the researchers called this “tuning”).

These findings are really important to finding new ways to eradicate mosquitoes. If researchers can find receptors that let mosquitoes recognize humans, they can start researching how to block this response. If the mosquito can’t find her next meal, the consequences are pretty obvious. Or, if researchers can figure out the main chemicals being recognized by the mosquitoes, they can design traps to lure the mosquitoes away from human populations. Importantly, these techniques wouldn’t involve giving medicine or treatments to people or interfering with their daily lives.