Ridding a region of malaria is, in theory at least, fairly simple. Female mosquitoes transmit the disease when they make a meal of infected blood, gestate the malaria-causing parasites (called sporozoites), and then inject them into the bloodstream of another victim at a later feeding. Break any part of that cycle, and the parasite can’t reproduce; keep up that effort, and you can halt any malaria epidemic. In practice, however, breaking the malaria cycle takes a lot of work. Italy and the American South have all but eradicated the disease by draining swamps, spraying insecticides, improving medication, and introducing air conditioners, screen doors, and mosquito nets. But for many places—including most of Africa—the resources for a broad, sustained effort are out of reach.
Which is why I found myself in a basement laboratory in central Italy last spring, peering into a cage of mosquitoes. The scientist in charge of the lab, Andrea Crisanti, a parasitologist and microbiologist at Imperial College London, has developed a technique that can spread a genetic modification through generations of the insects. “In one or two seasons, you can thoroughly attack an entire wild population at a chosen site,” he says. This breakthrough, heralded in Nature last spring, opens the possibility of replacing a region’s malarial mosquitoes with genetically modified competitors. Give them a trait that cuts the transmission of malaria, and the epidemic will likely be beaten. “We want to ask the mosquitoes to do what humans have not been able to,” says Crisanti, who is considering three promising approaches. One modification would render the insect unable to recognize the human scent. Another would significantly reduce the mosquito’s lifespan, giving the parasite less time to reproduce before dying along with its host. The one that Crisanti thinks is likeliest to succeed would kill female mosquitoes in the embryonic stage, leaving the males to spread the modification until the resulting sex imbalance caused the population to crash.