Simple mosquito killers are the new buzz in Gates Foundation’s malaria battle | The Seattle Times

Research team members check an attractive toxic sugar bait station on the outside wall of a home in Mali. In preliminary tests, the stations, which attract and kill malaria-carrying mosquitoes, caused populations of the bloodsuckers to plummet. (Westham Innovations)
Research team members check an attractive toxic sugar bait station on the outside wall of a home in Mali. In preliminary tests, the stations, which attract and kill malaria-carrying mosquitoes, caused populations of the bloodsuckers to plummet. (Westham Innovations)

Vaccines and genetic engineering grab the spotlight, but the Bill & Melinda Gates Foundation’s quiet funding for simple, new mosquito controls could be about to pay off in the effort to eradicate malaria.

 

Seattle Times science reporter

Since Bill and Melinda Gates galvanized the global health world with their 2007 call to eradicate malaria, researchers have been scrambling for new tools to get the job done.

The lineup includes headline-grabbing marvels like genetically engineered mosquitoes, a laser fence to zap the malaria-carrying bugs and a silver-bullet vaccine. But there’s no telling when — or if — any of those technologies will actually pan out.

Meanwhile, a less flashy Bill & Melinda Gates Foundation initiative could be about to pay off with two potentially game-changing new ways to kill mosquitoes. Though simple and environmentally friendly, both approaches crashed mosquito populations in initial field trials in Africa.

Private companies already exist to commercialize the products, which could be deployed within a few years. And both also show promise for helping Americans battle mosquitoes in their own backyards.

“There’s lots of innovation, lots of cool ideas for malaria, but we really need things that can start saving lives in a timeline of three to five years,” said Penn State University entomologist Matt Thomas. “Simply having a great idea that sits on the lab bench isn’t going to do that.”

Humble insecticides have been the workhorse of every successful malaria elimination drive, including those that banished the disease from the United States and Europe. Since 2000, malaria deaths worldwide have fallen by half, and almost 80 percent of the gains are attributed to wider use of insecticide-treated bed nets and indoor spraying.

It’s cheaper and easier to develop new methods of mosquito control than to develop and gain approval for new drugs or vaccines, said Dan Strickman, a senior program officer at the Gates Foundation. But mosquitoes will eventually develop resistance to any conventional insecticide. Almost since its founding the Gates Foundation has been quietly investing in research on novel insecticides — while also searching for entirely new ways to control mosquitoes.

The two new technologies, which Strickman says could be “transformational,” capitalize on mosquito behavior. One turns an entire house into a toxic trap using humans as bait. The other lures mosquitoes with the scent of their primary food — which isn’t blood.

“These are tools that don’t just replace something that we do now,” Strickman said. “They do something different.”

The house trap was dreamed up under a mango tree in a Tanzanian village where Thomas, Dutch entomologist Bart Knols and colleagues gathered for a brainstorming session.

 

One of the topics was an odd preference on the part of malaria-carrying mosquitoes for slipping into houses via the gap between the walls and roof that’s common in many African dwellings. The scientists came up with the idea of inserting plastic tubes, called eave tubes, under the roofline and closing off the rest of the gap.

The mosquitoes, which bite indoors at night, are lured into the tubes by the scent of humans in the house. But instead of a tasty blood meal, the insects encounter a pesticide-coated mesh insert that douses them with poison.

With funding from the European Union, the researchers tested the concept by building an experimental village inside a screened enclosure the size of two tennis courts. They seeded a small marsh with malaria-free mosquitoes to establish a self-sustaining population and recruited volunteers to act as bait, sleeping in houses equipped with eave tubes and window screens.

The results were “incredible,” Strickman said. “The mosquitoes were basically gone, without spraying, without a lot of use of insecticides.”

The Gates Foundation was so impressed that the giant philanthropy bypassed its normal funding channels and anted up $10.2 million for large-scale tests that will include malaria monitoring.

The work will start early next year in 40 villages in the West African nation of Ivory Coast. Half the villages will get eave tubes, while the other half will use conventional mosquito control, Thomas explained.

Computer modeling suggests that installing eave tubes in even half the homes in some African communities could have a significant impact on malaria, he added. After the initial cost of installation, the only expense would be replacing the insecticide-coated inserts a couple of times a year.

A Dutch company, In2Care, is already manufacturing the tubes and is part of the research. “This is a tool that can be made field-ready,” Thomas said.

Workers drill holes along the roofline of a house in Kenya to install eave tubes to kill malaria-transmitting mosquitoes. In initial trials, mosquito populations in the village crashed.  (Penn State University)
Workers drill holes along the roofline of a house in Kenya to install eave tubes to kill malaria-transmitting mosquitoes. In initial trials, mosquito populations in the village crashed. (Penn State University)

Eave tubes target mature female mosquitoes, which only feed on blood in order to produce eggs. The other new approach to mosquito-killing exploits the insects’ main food source — which is nectar.

Watching mosquitoes flit around flowers gave Israeli scientists the inspiration for using sugar to lure mosquitoes into a trap. The team got an early grant from the Gates Foundation, and was later funded by the U.S. military.

What emerged is the concept called attractive toxic sugar bait, or ATSB.

“It’s entirely new,” Strickman said. “There’s never been a real attract-and-kill product for mosquitoes before.”

The idea is to use a bait that draws mosquitoes with its sweet scent, but is mixed with a small amount of insecticide. “As long as the mosquitoes come and feed on these things, they’re going to die,” Strickman said.

It took years of trial and error with solutions ranging from guava juice to fermented fruit brews for the scientists to develop a long-lasting, patented bait based on dates and sugar. A variety of insecticides can be used, including benign compounds like boric acid and garlic oil.

Tests in Israel and West Africa showed that use of toxic sugar bait, either as a spray or bait stations, can reduce mosquito populations by 90 percent or more. It seems to work well even in places with a lot of natural sugar sources, like flowers and rotting fruit.

The approach is especially powerful because it can kill males and young females, Strickman said. But early versions also killed bees and other pollinators. The newest bait stations, which encapsulate the lure and insecticide in a flat, black membrane, don’t seem to attract beneficial insects, but more research is needed, said University of Miami environmental health expert John Beier, a member of the project science team.

The Gates Foundation is funding large trials in Mali through the UK-based Innovative Vector Control Consortium.

The Israeli-based manufacturer Westham Co. is a key player in the trials and is already thinking about how to gear up for commercial production, Strickman said. Equipping a house with two long-lasting bait stations could cost as little as $5 and could be enough to control local mosquito populations, he added.

“We hope to have a product in Africa on the market as early as 2019,” Strickman said.

Research on eave tubes and toxic sugar baits has already generated products for mosquito control in the U.S. and other developed countries.

Researchers tested the effectiveness of attractive toxic sugar bait stations on mosquitoes released inside screened enclosures in the West African nation of Mali.  (Westham Innovations)
Researchers tested the effectiveness of attractive toxic sugar bait stations on mosquitoes released inside screened enclosures in the West African nation of Mali. (Westham Innovations)

Americans can buy a sugar-based spray from Terminex that kills mosquitoes with garlic oil, or hire the company to have their property sprayed. Backyard bait stations aren’t available yet but eventually will be, Beier said.

“I would certainly buy one at Home Depot if I could,” he said.

In2Care, the company that makes eave tubes, also produces stand-alone mosquito traps that use the same type of insecticide-coated mesh to deliver the fatal dose. The traps were recently approved for emergency use in the U.S. against the mosquitoes that transmit Zika, dengue and other viruses.

Funding from Gates and others has created a golden age in what’s called vector control — the unglamorous slog of battling mosquitoes, said Karl Malamud-Roam, manager of Rutgers University’s public health pesticides program.

“There hasn’t been any time in the last hundred years when so many new … ideas have been floating around, with people who care and money to test things,” he said.

For malaria, the next challenge will be to figure out what mix of mosquito killers will work best in combination with existing medical treatments to beat back the disease and shrink its footprint over the next 10 to 15 years, he said.

By that time, some of the futuristic techniques like genetic engineering or a better vaccine might be ready for prime time, said Thomas, of Penn State.

“Hopefully, at that point they will be just mopping up.”

Some of the reporting for this story was conducted during a fellowship sponsored by Malaria No More, which is partly funded by the Bill & Melinda Gates Foundation.

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