2009-06-28

Aedes Aegypti is a tricky enemy with a dangerous weakness for travel. Unlike other mosquitoes, it can survive the cold and thrives on city life. The increase of international trade and the accelerating pace of urbanization have broadened its horizon with grim consequences. The disease it carries, dengue fever—debilitating and sometimes lethal—is spreading fast. More than 100 million people in 100 countries are afflicted every year. Fatality rates can top 20 percent. There is no vaccine, no cure and no solution—none, at least, that conventional medicine can offer.

A new strategy involves a subtle reconfiguring of the bug's DNA. Scientists working in labs near Oxford have devised a genetic modification that sterilizes the male Aedes, transforming the critter into his own worst enemy. He can still mate—but he can't breed. Any offspring dies before becoming fully developed. The idea is to release a huge, all-conquering swarm of the doctored insects into the wild, let them find partners among the native females and wait for the mosquito population to decline. Preliminary trials, looking at both safety and effectiveness, have already taken place in Malaysia. Within a few years, the Franken-insects could be airborne.

The idea of GM mosquitoes was first floated 20 years ago. But it's only recently gained the support of mainstream health officials. The Bill and Melinda Gates Foundation has invested $38 million into the research. In May, experts from around the world gathered in Geneva for a meeting sponsored by the World Health Organization to discuss progress and develop global guidelines for testing. Some environmental groups are alarmed at the development, and a confrontation looks certain. This is one they may lose. Unlike GM crops, whose benefits have more often gone to farmers, GM insects address a global health problem that causes great human suffering and death.

Dengue fever may be only the start. Researchers are tweaking the genome of the Anopheles gambiae mosquito, the species that carries the malaria parasite, which kills at least a million people each year. Scientists hope to produce, say, a mutant bug with a superboosted immune system capable of killing off the parasite or loaded with an extra gene to block its development.

The practice of displacing pests with sterile mates has been common practice for 50 years. Every week, Guatemala, Mexico and the U.S. irradiate 2 billion male Mediterranean fruit flies before releasing them to search out mates. What's new, of course, is the use of genetic manipulation instead of irradiation, which tends to leave Aedes too weak to pursue females. By slipping a single gene known as OX513, a composite partly derived from coral, into its DNA, British scientists believe they can doom any progeny beyond the larva stage.

To an eco-aware generation, already fearful of genetically modified food, any tinkering with the world's delicately balanced ecosystems is unacceptable. "The inherent arrogance of believing that you can control the outcome is outrageous," says Gillian Madill, a genetic-technologies campaigner at Friends of the Earth in Washington. Besides, the argument goes, malaria is already both preventable and curable without recourse to bolder and more risky tactics. A battery of effective drugs, notably artemisinin, is now available, and aid agencies have had success with bed nets drenched in insecticide.

Malaria, though, remains a formidable foe. There are signs of a developing resistance to the drugs, including artemisinin. Malaria is reemerging in parts of Southeast Asia, and many countries are struggling to meet their target of reversing the spread of malaria by 2015, one of the Millennium Development Goals set by the U.N. Progress toward a vaccine has been slow. "We know today that we won't be able to control or eradicate the parasite unless we tackle the vector [the mosquito]," says George Christophides of Imperial College in London.

Environmental groups are being forced to take the morally precarious path of arguing against technology that could save the lives of millions of poor people. The population of sub-Saharan Africa accounts for more than 85 percent of all the world's malaria cases, and loses at least 750,000 people a year to the disease. Africans can't afford the same anxieties as people in North America have shown over GM crops. "Malaria is different because we in the West don't have it," says Arthur Caplan, professor of bioethics at the University of Pennsylvania. "If you are sitting with your pregnant wife in a hospital in Tanzania or Malawi, then you are not going to be so worried about the escape of a few mosquitoes."

The scientific establishment is not taking public acceptance for granted. The WHO is devising rules for testing GM mosquitoes to ensure that a foreign gene could not find its way into other organisms. Three new biosafety-training centers are planned in Africa, Asia and Latin America. "As a community, we are trying to take an extraordinarily cautious approach," says Paul Eggleston of Keele University in England. Modifying the mosquito may be a risk worth taking, but it won't be taken without public support.

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