Magazine article Newsweek

Zika Reviving Decades-Old DDT Debate, but Here's Why It's Unfounded; Conservative Publications Are Pushing the Return of DDT, but Experts Say That's Ridiculous

Magazine article Newsweek

Zika Reviving Decades-Old DDT Debate, but Here's Why It's Unfounded; Conservative Publications Are Pushing the Return of DDT, but Experts Say That's Ridiculous

Article excerpt

Byline: Zoe Schlanger

Last week, at the bottom of a New York Times story about the Zika virus outbreak, an old and controversial chemical made a brief appearance. DDT, the insecticide made famous for its environmental consequences by Rachel Carson's 1962 book, Silent Spring, was being "mentioned a bit" in public health circles as a possible means to eradicate the Zika-carrying mosquito, Aedes aegypti, wrote the Times.

DDT works as a neurotoxin, killing mosquitoes and other pests brain-first. Scientists determined decades ago that DDT causes serious environmental damage, leading the U.S. to ban the chemical in 1972; the 150 parties to the 2001 Stockholm Convention agreed to put an end to its use too. More recent studies have drawn connections between DDT and neurotoxic health effects in humans, like Alzheimer's, Parkinson's disease, breast cancer, diabetes and impaired brain development in children.

These concerns, said Lyle Petersen, director of the division of vector-borne diseases at the Centers for Disease Control and Prevention, need to take a backseat in the face of the hazards of Zika. DDT, he argued, could be used in small amounts on the walls inside homes; the environmental damage widely associated with the insecticide was tied with large-scale agricultural use, and scale matters. "That concern about DDT has to be reconsidered in the public health context," he told the Times.

But according to Joe Conlon, a technical adviser to the American Mosquito Control Association and a former entomologist with the U.S. Navy, using DDT to control Zika is a terrible idea. "DDT seems like a silver bullet, but it isn't." First of all, the mosquitoes might be resistant to DDT. Conlon says the Latin American countries where Zika is blooming now used DDT heavily in the 1960s to kill off the Aedes aegypti, which also carries diseases like dengue and yellow fever. It worked, but the mosquitoes in the region developed robust resistance to the pesticide, which may still be lingering in the population. DDT resistance lasts a long time, he says, because the chemical persists in the environment so long. If you spray a wall with DDT today--a method commonly used because mosquitoes are known to rest on walls a moment after having a blood meal--it could still be coated by DDT in 20 years. The mosquito population continues to be bombarded by the chemical, so the resistance shows up in every subsequent mosquito generation.

And even if the mosquitoes aren't already resistant, they will be. It only takes a "few generations" of mosquito to develop resistance, and when an Aedes mosquito's life span is about 10 days, that's not long at all. Conlon speculates mosquitoes could develop resistance within a year. "What's even worse, resistance to DDT can stir cross-resistance to the other pesticides we use, like the pesticide we use to treat bed nets, to fight malaria."

In the end, Conlon says, there may be no good chemical solution to the Zika mosquito. …

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