Mosquitos carrying Zika may have an Achilles heel

A Miami-based researcher and his team are hoping to make humans undetectable to the Aedes aegypti.

The workplace of neurogeneticist Matthew DeGennaro, on the campus of Florida International University in Miami, doesn’t look especially high tech. The Laboratory of Mosquito Genetics and Behavior is filled with metal shelving and neatly labeled plastic tubs—it could be a bread-baker’s simple pantry. But looks can deceive.

DeGennaro and his team are using advanced technology to cook up tools to do battle with the Aedes aegypti mosquito, the primary carrier of Zika as well as dengue and yellow fever, and a particularly nasty virus called chikungunya.

DeGennaro explains the scope of the problem in no uncertain terms, “Worldwide, approximately 725,000 people die every year because of mosquito-borne illness.”

Combine that with the fact that about 300 cases of Zika have shown up in Miami-Dade County since January, and you can see what’s motivating these scientists to think hard about these mosquitos.

DeGennaro and his crew aren’t the only team working on this problem—in fact, humans have tried for a century to exterminate Aedes aegypti, with no success—but this group thinks they’ve found an Achilles heel of sorts in the pest that they hope to exploit.

“Mosquitoes are born with the knowledge of how to find a human host,” DeGennaro explains. “The primary way mosquitoes find people is using their sense of smell.”

The bacteria on our skin metabolizes our sweat and produces an odor that appeals mightily to the females, the only ones that bite. DeGennaro says to think of it this way: If you’re a big meat eater and you haven’t eaten for a few days, then someone serves you up a delicious-smelling, perfectly cooked roast beef. And DeGennaro’s team is trying to create mosquitos that simply can’t smell us. If they can’t find us, they can’t nourish their eggs and reproduce. Nor can they spread disease to us.

His team has a powerful tool at its disposal—a gene editing technique called clustered regularly interspaced short palindromic repeats, or CRISPR, for short.

“It’s [a] way of specifically going into that genome, taking a nucleus, and it just cleaves the gene, just at one spot. Just the gene you’re interested in,” DeGennaro explains. “It’s an amazing technique that has revolutionized biology in all sorts of ways.”

It takes about six months to create a batch of modified mosquitos, and then it’s testing time. To see whether it’s working, a tester puts his arm in a box behind a screen and other team members send in the mutants. The ones that are attracted bang up against the screen, trying to get to the arm. In this way, researchers can tell whether they have genetically affected the insect’s sense of smell.

“We are getting closer,” he says. “I think we’re making progress. I’m hopeful that we can use this knowledge to really deeply understand how mosquitos smell the world and particularly how they smell people.”

The team is also using the results of their genetics experimentation on the Aedes aegypti to develop attractants and repellents to control mosquito behavior.

“You can actually make a repellant by making ourselves invisible to them,” says DeGennaro. “By blocking their sense of smell with a designer perfume. We and others hope to identify such chemicals and use them to hide people from mosquitos.”

Another group using genetics to approach the Aedes aegypti problem is the British company Oxitec. They’re modifying male mosquitos so that, when they mate with females, their offspring will die almost immediately. The company’s plans to test these mutants on a small island near Key West have become fodder for intense public debate. A referendum on whether they may release them in the wild will appear on the November 8th ballot.

Until then, DeGennaro’s lab will continue to focus on smell. And the stakes are high.

“This is not about making a redder tomato,” DeGennaro says. “This is about blocking a disease that is making it less safe for women to have children in Miami. And across the world.”