Better mosquito-killing through science
▶ Among the trial methods: genetic engineering, radiation, larvicide ▶ “We don’t really have any method that’s working”
Until there’s a vaccine or treatment for the Zika virus, the quickest way to control its spread is to attack the mosquitoes that carry it. Biotech companies and governments are wielding their best weapons, all of which involve breeding the bloodsuckers in labs and applying treatments that render them unable to reproduce or spread viruses, then releasing them into the wild.
In Brazil, Oxitec says it expects approval within weeks to sell the government a bioengineered mosquito incapable of having offspring. If there are enough sterile mosquitoes in the mating pool, fewer new ones will be born. Oxitec, a British subsidiary of U.S. biotech company Intrexon, has conducted trials in South America since 2009 and already has a facility in Brazil that can breed 2 million genetically modified (GM) mosquitoes in a week. “We’re very much operational,” says Chief Executive Officer Hadyn Parry.
The United Nations International Atomic Energy Agency has offered to show Brazilian authorities how to sterilize male mosquitoes with radiation. The technique is widely used to control agricultural pests. Australian scientists say they might be able to block transmission of Zika by infecting mosquitoes with a naturally occurring bacterium. And Mosquitomate, a Lexington, Ky.-based startup, is experimenting with a way to dust the bugs with a hormone-based larvicide.
These strategies mark a sharp departure from the old pesticide-centric method of “spray-’n’-pray.” So far, “we don’t really have any method that’s working,” says Paul Reiter, a consultant on insect-borne disease who’s worked at France’s Institut Pasteur and the U. S. Centers for Disease Control and Prevention.
Mosquitoes have developed resistance to DDT and many of the synthetic pyrethroid compounds used to treat mosquito nets. The Aedes aegypti mosquito, which spreads Zika and dengue fever, is rapidly proliferating in tropical cities, where it can breed in showers, toilet tanks— even in discarded bottle caps. The World Health Organization, describing A. aegypti as “an opportunistic and tenacious menace,” on Feb. 16 urged countries “to boost the use of both old and new approaches to mosquito control.”
Oxitec says it’s readying a Brazilian factory to produce 60 million GM mosquitoes a week, but that would cover an area with only about 60,000 people. While the British company won’t disclose construction costs, they could easily run into the tens of millions of dollars. A decade ago, it cost $8.4 million to build a facility in Brazil capable of breeding and irradiating 200 million Mediterranean fruit flies weekly, according to a 2011 study published by Oxitec scientists. The breeding facilities for the other treatment methods have similar requirements.
Introducing treated mosquitoes into the general population presents special challenges. They’re too fragile to
drop from planes. Oxitec will use trucks to spread its genetically modified insects. The UN is working with a German company to develop delivery by drone.
Once the mosquitoes reach their destination, though, they’ll begin annihilating themselves, and that’s a big advantage, says Mosquitomate founder and CEO Stephen Dobson, an entomology professor at the University of Kentucky. Says Dobson: “We let the mosquitoes do the work for us.” �Carol Matlack, with Jason Gale and Jonathan Tirone The bottom line Several new anti-mosquito treatments seek to introduce lab-bred bugs that can’t reproduce or transmit viruses.