DEET-free mosquito repellents on the way

The Bill & Melinda Gates Foundation didn't have Americans in mind when it started pouring money into research on mosquito-borne diseases more than a decade ago. The goal was to save lives and reduce suffering in the developing world, where malaria and other deadly fevers run rampant.

So is it selfish to ask if there's anything in it for us?

More specifically: Are all these studies ever going to yield a replacement for DEET?

With cautious caveats, many researchers are convinced the answer is finally "yes."

Thanks in part to an infusion of cash from the world's biggest philanthropy, understanding of the mosquito's astounding sense of smell has advanced rapidly in the past few years. Now, those insights are poised to pay off in the form of better products to block the bloodsuckers' ability to sniff us out.

"We are on the cusp of making major discoveries," said Anandasankar Ray, a neurobiologist at the University of California, Riverside, who leveraged a seed grant from Gates to land federal funding for his studies.

Most experts caution that it's likely to be five years or more before hikers, sportsmen and picnickers can wash their hands of the greasy, DEET-laced lotions and sprays that dominate the market today.

Ray is more optimistic, as befits a man who has already spun off one company, called Olfactor Laboratories. "At least some of these things could be available within a year," he predicted.

The first might be the Kite Patch, a 2-inch cloth square unveiled by Olfactor this summer. Fasten the chemical-impregnated patch to your clothes, the company claims, and it creates an aerosol shield that renders you invisible to mosquitoes for 48 hours. The technology grew out of Ray's Gates-funded project, which identified common, nontoxic compounds that can wreak havoc with the mosquito's ability to detect the carbon dioxide exhaled by potential prey.

"One of the strongest, if not the strongest, attractive cue for mosquitoes and any blood-feeding insect is a turbulent plume of CO2," Ray said. "That's how they know a living vertebrate is in the vicinity."

Before it can be sold in the U.S., the Kite Patch must receive safety certification and undergo independent tests to verify that it works.

Approval can't come soon enough for the nearly 12,000 fans who donated $557,254 to Kite Patch's recent crowdfunding campaign. The money will be used for field trials in Uganda, and donors are first in line for patches if the product makes it to market here.

But some scientists caution that a repellent that only shuts down CO2 sensors could run into an obstacle that has confounded many attempts to trick one of mankind's oldest adversaries. In the female mosquito, evolution has crafted the biological equivalent of a guided missile with multiple methods to lock in on a target and ensure she gets the blood she needs to produce eggs.

"Mosquitoes are smarter than we are," said Leslie Vosshall , a neuroscientist at The Rockefeller University in New York City. "They have other ways to detect us."

Wisps of carbon dioxide may draw the insects in from afar. But mosquitoes have more than 80 types of odor receptors in their "noses" -- which are actually appendages on the head called maxillary palps. Each type is tuned to a specific scent, from the lactic acid in sweat to compounds in breath and the skunky aroma of feet, which many species find irresistible.

Every human has a unique scent signature, which is probably why mosquitoes pester some people but barely buzz others.

Vosshall was part of a consortium that received a $5 million Gates grant in 2005 to study the mosquito nose, at the same time a group headed by Larry Zwiebel at Vanderbilt University got $8.5 million.

The foundation has since pulled back from big grants for basic research and doesn't fund much work on repellent anymore.

But that initial investment kick-started what was really a "fringe field," Vosshall said.

Scientists now have a much clearer molecular-level picture of mosquito olfaction -- and how complicated it is. They've developed methods to quickly screen thousands of compounds for repellent-worthiness, and have identified several tantalizing candidates.

"We have a suite of compounds that could really be the next generation in intelligent mosquito -- and other insect -- repellents," Zwiebel said.

At the U.S. Department of Agriculture's Mosquito and Fly Research Unit in Gainesville, Fla., Ulrich Bernier and his colleagues also have a lineup of chemicals that repel mosquitoes more effectively and last longer than DEET.

The lab is a successor to the one where USDA scientists developed DEET in collaboration with the military. In the aftermath of World War II, researchers screened hundreds of compounds the old-fashioned way: by having volunteers stick their arms in cages full of hungry mosquitoes.

Bernier still uses the technique, serving as his own guinea pig. But he also relies on computer algorithms to design and synthesize new repellents and lures that can be used to trap mosquitoes.

Yet after all these decades, no one is certain how DEET works its magic.

Vosshall believes she's close to cracking the mystery. Her experiments have shown that mosquitoes robbed of their sense of smell are impervious to DEET. That's strong evidence that the repellent does act as a cloaking device that prevents mosquitoes from smelling their human prey.

Mosquitoes also seem repulsed by the chemical's taste, which they detect through taste buds on their feet when they land on DEET-slathered skin.

Vosshall has a project in the works which she hopes will settle the remaining questions. "My feeling is that you can't improve on current technology unless you understand how the current technology works," she said.

But she understands the world's impatience.

"When I go on a trip with my friends and relatives, they say: 'Leslie, enough talk! When is there going to be a product?'?"

(Reach Seattle Times writer Sandi Doughton at Distributed by Scripps Howard News Service,

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