We Have the Technology to Destroy All Zika Mosquitoes
Fear of the Zika virus could generate support for gene drives, a radical technology able to make species go extinct.
A controversial genetic technology able to wipe out the mosquito carrying the Zika virus will be available within months, scientists say.
The technology, called a “gene drive,” was demonstrated only last year in yeast cells, fruit flies, and a species of mosquito that transmits malaria. It uses the gene-snipping technology CRISPR to force a genetic change to spread through a population as it reproduces.
Three U.S. labs that handle mosquitoes, two in California and one in Virginia, say they are already working toward a gene drive for Aedes aegypti, the type of mosquito blamed for spreading Zika. If deployed, the technology could theoretically drive the species to extinction.
“We could have it easily within a year,” says Anthony James, a molecular biologist at the University of California, Irvine.
Any release of a gene drive in the wild would be hotly debated by ecologists. So far, no public health agency has thrown its weight behind the idea. But with Zika sowing fear across Latin America and beyond, the technology is likely to get a closer look. “Four weeks ago we were trying to justify why we are doing this. Now they’re saying ‘Get the lead out,’” says James. “It’s absolutely going to change the conversation.”
The Zika virus is now spreading “explosively" in the Americas, according to the World Health Organization, which last week declared a global health emergency. While the virus causes only a mild rash, the epidemic is frightening because of a suspected link to 4,000 children born in Brazil with microcephaly, or shrunken heads.
There’s no easy way to stop Zika. There is no vaccine and developing one could take several years. Brazil is sending 220,000 soldiers door-to-door to check for mosquitoes breeding in old tires and swimming pools. Women are being asked to delay pregnancy.
Gene-drive technology could be ready sooner than a vaccine, but it’s no quick fix, either, scientists caution. Self-annihilating mosquitoes will first have to undergo tests in the lab, then perhaps on an island, before they could be released more broadly. Regulations and public debate could stretch the time line out for years.
The Aedes aegypti mosquito is not native to the Americas. It’s an invasive species that is now found from Florida to Argentina and whose range could expand with climate change. In addition to the Zika virus, its bite also transmits the chikinguya and dengue viruses. Dengue fever causes 100 million people to fall ill each year.
Because of the extent of the problems Aedes aegypti causes, some scientists favor using advanced technology to drive the species to extinction, at least in the Americas. “These mosquitoes truly have little value,” says Zach Adelman, an entomologist at Virginia Tech who works with Aedes aegypti. “People in favor of eradication are going to be able to plead their case.”
While gene-drive technology could save human lives, the feature that makes it so powerful—that mosquitoes themselves spread it—also raises concerns over unforeseen ecological consequences. What if the DNA change somehow jumps to other insects? If things were to go wrong, would scientists be able to recall it? An expert panel of the National Academy of Sciences, in Washington, D.C., is expected to release a report in May on responsible use of the technology. “I don’t think there is a real consensus yet on gene drives,” says Keegan Sawyer, director of the study. “There are differing camps.”
Todd Kuiken, an environmental scientist who studies governance of new biotechnology for the Woodrow Wilson Center in Washington, D.C., says even an invasive species might be filling a useful biological niche. “I don’t think the entire ecosystem is going to collapse if you removed an invasive, but there is a lot of interconnectedness between species, especially in the tropics,” he says. “My concern is more the ecological interactions.”
The technology is still extraordinarily new. The systems work because scientists are able to weave gene-editing machinery directly into an insect’s DNA. That way, instead of a given gene passing to half of a mosquito’s offspring, as would normally happen, it spreads to all of them, a phenomenon dubbed “super inheritance.”
Depending on the genetic payload scientists choose to spread, they could eradicate insects or make them unable to spread disease.
The latter tactic, called “population replacement,” works by spreading a gene that makes mosquitoes unsuitable hosts for a pathogen so they won’t infect people. This approach was taken by James and collaborators last November, when, working in a secure lab, they developed a drive that spread a gene among mosquitoes which blocks the malaria parasite from developing (see “With This Genetic Engineering Technology There Is No Turning Back”).
But a gene drive can also make mosquito populations disappear. The simplest way to do that is to spread a genetic payload that leads to only male offspring. As the “male-only” instructions spread with each new generation, eventually there would be no females left, says Adelman. His lab discovered the Aedes aegypti gene that determines sex only last spring. The next step will be to link it to a gene drive.
Kevin Esvelt, a gene-drive researcher at MIT’s Media Lab who has been outspoken about the need to proceed cautiously, also thinks Aedes aegypti eradication should be the goal, so long as the public is onboard and the safety of the idea proved.
“Technologically, we could probably do it in a couple of years,” says Esvelt. “I’m sure we’ll be able to do it before people can agree if we should.”
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September 11-14, 2018
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