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Brazilian town fighting Zika mosquitoes with more mosquitoes

Millions of genetically-modified mosquitoes are being released in the Brazilian town of Piracicaba with the hope that they'll take out Zika-infected mosquitoes
Millions of genetically-modified mosquitoes a... 02:08

PIRACICABA, Brazil --The town of Piracicaba is taking a very different approach in its battle against Zika -- it is fighting mosquitoes with more mosquitoes. Millions more.

"We release 800,000 mosquitoes a week in this neighborhood," biologist Cecilia Kosmann told CBS News.

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Cecilia Kosmann rides in a van from which she releases genetically modified mosquitoes. CBS News

But the mosquitoes that Kosmann releases are genetically modified by a British firm, Oxitec, to contain a lethal gene. In order to survive, the engineered insects need an antibiotic, which they receive while they're raised in the lab.

Then they're released so they will mate in the wild. Outside the lab, without the antibiotic, they die, as do their offspring who carry the same lethal gene.

"If we fight the mosquito, we are fighting every disease that that mosquito can transmit," Kosmann explained.

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Mosquitoes in a lab in Piracicaba, Brazil. CBS News

The Aedes aegypti mosquito can breed in almost any standing water -- drainage ditches, the bottom of a trash bag, a simple puddle. So breeding sites are constantly monitored. A second gene alteration makes the modified larvae fluorescent, so they're easy to count.

The company says the larvae population in the area dropped by 82% in less than a year.

"We know we can eradicate the Aedes aegypti mosquito," said Dr. Peter Hotez, one of the leading tropical disease experts in the world.

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Genetically modified mosquitoes are released to help fight Zika. CBS News

Dr. Hotez says an aggressive international campaign led to the near eradication of Aedes aegypti back in the 1970's. But the species has rebounded.

"I think we can evaluate these new technologies. It's worth evaluating them at scale, but that should not stop efforts right now using traditional methods," Dr. Hotez said.

Key West, Florida has applied to the FDA to conduct a test using the very same modified mosquitoes, although it's run into opposition from local residents who say it's too soon to understand the environmental impact.

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