KEY WEST, Florida (AP) — Millions of genetically modified mosquitoes could be released in the Florida Keys if British researchers win approval to use the bugs against two extremely painful viral diseases.

Never before have insects with modified DNA come so close to being set loose in a residential US neighborhood.

“This is essentially using a mosquito as a drug to cure disease,” said Michael Doyle, executive director of the Florida Keys Mosquito Control District, which is waiting to hear if the Food and Drug Administration will allow the experiment.

Dengue and chikungunya are growing threats in the US, but some people are more frightened at the thought of being bitten by a genetically modified organism. More than 130,000 signed a Change.org petition against the experiment.

Even potential boosters say those responsible must do more to show that benefits outweigh the risks.

“I think the science is fine, they definitely can kill mosquitoes, but the GMO issue still sticks as something of a thorny issue for the general public,” said Phil Lounibos, who studies mosquito control at the Florida Medical Entomology Laboratory. “It’s not even so much about the science — you can’t go ahead with something like this if public opinion is negative.”

Mosquito controllers say they’re running out of options that can kill Aedes aegypti, a tiger-striped invader whose biting females spread these viruses. Climate change and globalization are spreading tropical diseases farther from the equator, and Key West, the southernmost US city, is particularly vulnerable.

“An arriving person would be infectious for several days, and could infect many of the local mosquitoes,” Doyle said. “Within a few weeks you’d likely end up with several infected mosquitoes for each infected visitor.”

There are no vaccines or cures for dengue, known as “break-bone fever,” or chikungunya, which causes painful contortions. US cases remain rare for now, but dengue sickens 50 million people annually worldwide and kills 2.5 percent of the half-million who get severe cases, according to the World Health Organization. Chikungunya has already overwhelmed hospitals and harmed economies across the Caribbean after infecting a million people in the region last year.