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Scientists want to release millions of genetically-modified mosquitos in Florida. Here's why.

Scientists want to release millions of genetically modified mosquitos in the Florida Keys, all for the sake of public health.

Really.

Researchers with British biotech company Oxitec want to use the mosquitos as a weapon against other mosquitos who are spreading two deadly fevers, dengue and chikungunya. The two fevers have both had outbreaks in the US this year, and pose a growing threat to Americans. The Florida Keys Mosquito Control District wants to use the experiment to control the region's problematic mosquito population.

There isn't a licensed vaccine or treatment for dengue. So, scientists have turned their efforts to targeted the mosquitos that infect people, fighting them with genetically-modified mosquitos developed by a British biotech firm. Here's how they're modifying the insects.

How does it work?

mosquito

Marcos Teixeira de Freitas/ Flickr

The process starts with tiny mosquito eggs. Researchers inject them with very small amounts of DNA that the biotech firm manufactured. Many of the mosquitos don't survive this process, and others don't take on the DNA as their own. But in a few mosquitos, the DNA does take, and works its way into the insect's genome, making the mosquitos sterile.

The eggs will hatch, and scientists will monitor them. If the DNA injection works in the sperm cells of a male mosquito, or the egg-producing cells of a female mosquito, the DNA can be passed along to the next generation. Those insects are bred with other mosquitos, with the hope that the DNA will be passed on.

The sterilized male mosquitos compete with wild male mosquitos to mate with female mosquitos that spread the fevers. When the modified mosquitos win, the female don't reproduce — and the spread of disease (hopefully) slows.

Some scientists urge a cautionary approach in releasing genetically modified insects, because researchers are not exactly sure how it will play out when the mosquitos are released en masse into an environment. Hellen Wallace, a genetic modification researcher, explained the danger in a 2011 editorial in Scientific American.

"On release, GM [genetically modified] mosquitoes become part of a complex system involving predators and prey, other mosquito species, four types of dengue virus, other tropical diseases transmitted by mosquitoes, and the humans—including children—who are being bitten and infected."

There's concern that genetically modified mosquitos might bite people and cause harmful effects. Oxitec aims to mostly use male mosquitos, because they don't bite. In a trial of the mosquitos in the Cayman Islands, only one female mosquito was released for every 3,000 male ones. For anything to be transmitted in a mosquito bite by one of those rare females, the genetically engineered proteins would have to be in the insect's saliva. Oxitec says there aren't any introduced proteins in the salivary glands of their mosquitos.

How do we know it will work?

We don't for sure. Because each environment is different, it's not entirely predictable how successful the release of genetically modified insects will be in controlling the target population of infected mosquitos. It all depends on how well the sterilized male mosquitos compete against wild ones in mating with the female mosquitos. But evidence from previous trials shows this is a valid approach.

One trial in the 1970s tested the effectiveness of using genetically modified sterile mosquitos to eliminate a mosquito population in El Salvador. There, 4.4 million mosquitos were released over an area of about six square miles. The sterile mosquitos wiped out the target mosquito population, though the chemical sterilization used on them would probably not be allowed in current techniques.

Oxitec first released its genetically modified mosquitos in 2009 on the Cayman Islands in the Caribbean. A trial of one strain of the insect found that when the genetically modified mosquitos were released into the wild, they mated successfully with female mosquitos over the four weeks they were studied.

A larger trial in Grand Cayman in 2010 saw an 80 percent reduction in the mosquitos that spread dengue, chikungunya, and yellow fever. The company has since released the modified insects in Malaysia and Brazil.

The proposal to use the insects in the Florida Keys is under review by the FDA, so it's not a go quite yet. But Oxitec has had success in working with US regulators on trials using genetically modified insects. The US Department of Agriculture assessed Oxitec's release of over 15 million genetically modified moths, and the moths behaved how scientists predicted they would. No negative outcomes to the environment, agriculture or human health were detected.