The Next Step in Malaria Prevention May Be to Make People Taste Bad

Desperate parents of nail-biting kids and furniture-chewing dogs often turn to foul-tasting compounds to deter their loved ones’ gnawing. In the future, we might be trying something similar with mosquitoes, as scientists now say that malaria-causing mosquitoes use scent and taste to decide who to bite. They published their research in the journal Nature Communications.

The mosquito, that scourge of summer, is more than just a nuisance. Mosquito-borne viruses like Zika and dengue are on the rise. Rates of malaria are down, but still high; around 214 million people were affected in 2015 alone. As drug developers race to develop vaccines, other scientists are hoping to find ways to keep disease-carrying mosquitoes from biting in the first place. To do that, they’ve got to know mosquitoes inside and out.

A mosquito lives by its noses. Yes, noses, plural. Every mosquito has three sets of scent-detecting parts: two antennae, two fuzzy mouthparts called maxillary palps, and two little spots called labella at the end of its proboscis. The antennae and palps are scent-only, but the labella contain neurons for sensing both smell and taste.

That’s a lot of olfactory information for a teeny tiny brain to take in. To find out how the mosquitoes do it, researchers tinkered with the genes of the malaria-carrying mosquito Anopheles gambiae. They tricked out the mosquitoes with a gene that would cause cells called odorant receptors (ORs) to glow bright green, which would make them easier to spot under a microscope. Building fluorescent proteins into bug parts is not a new technique, but it’s never been done before in mosquitoes.

This is a female Anopheles gambiae mosquito with olfactory neurons on the antennae, maxillary palp, and labella labeled in green. Image Credit: Olena Riabinina and Courtney Akitake, Johns Hopkins Medicine

 
By looking at the mosquitoes’ glowing ORs, the team was able to trace the paths from the pests’ sense organs to their brains. They found that information taken in by the antennae and maxillary palps was sent to brain regions called antennal lobes (this process is the same in flies). But signals from the labella went over to an area called the subesophageal zone—an area that had previously only been associated with taste.

The researchers say this likely means that a mosquito not only sniffs us but tastes us, too, poking with the end of its proboscis to confirm we’re edible before unsheathing its gross, syringe-like feeding needles.

It’s an unsettling concept, to be sure, but it might just help us out down the road. Co-author Christopher Potter, a neuroscientist at Johns Hopkins University, says we could use An. gambiae's brain cells against it—all we have to do is convince it that we taste terrible. “Our goal is to let the mosquitoes tell us what smells they find repulsive and use those to keep them from biting us,” he said in a statement.

Lead author Olena Riabinina, now at Imperial College London, noted that their success with the glowing protein has created new possibilities for mosquito research. “We were pleasantly surprised by how well our genetic technique worked and how easy it is now to see the smell-detecting neurons,” she said. “The ease of identification will definitely simplify our task of studying these neurons in the future."

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