Don't Let the Bugs Bite: Can Genetic Engineering Defeat Diseases Spread by Insects?

Article excerpt

Celia Cordon-Rosales wants to build a ghost town. A dozen small thatch and adobe huts would stand in several clusters. A few pigs would occupy nearby pens, insects would buzz to and fro, and bacteria would live out unremarkable lives. But the mock hamlet would be devoid of human residents. It would also be enclosed in nets of mesh so fine that nothing as large as a bug could escape. And a ditch would encircle everything to collect any runoff water that might permit microorganisms to leave the site.

All in the name of entomology.

Such an elaborate and carefully contained field site is needed for her research on Chagas' disease, says Cordon-Rosales, who works at the Universidad del Valle de Guatemala in Guatemala City. Chagas' is one of several insectborne diseases that she and other researchers are aiming to take on through genetic engineering. Given the potential problems with releasing genetically modified organisms--either microbes or the insect vectors that carry them--scientists are incorporating extraordinary precautions into their research plans.

People contract Chagas' disease via infection with Trypanosoma cruzi. These single-celled protozoa get shuttled among people and animals by several species of insects called kissing bugs or assassin bugs. The bugs feed on the blood of many mammals and leave behind feces laden with parasites that can then enter the body.

The insects, which get one of their nicknames from a tendency to bite people near the mouth, infest huts and other rudimentary dwellings throughout much of Latin America. Kissing bugs and the trypanosomes that they carry range as far north as the United States, although Chagas' infections north of Mexico occur primarily in wild animals.

Of more than 90 million people living where Chagas' disease is endemic, an estimated 12 million to 18 million are infected. Between 10 and 30 percent of those infected subsequently develop heart failure or other chronic, life-threatening symptoms, and about 50,000 people die from the infection each year. There is no vaccine or cure for Chagas' disease.

Cordon-Rosales and her U.S. collaborators are also targeting malaria, sleeping sickness, and dengue and yellow fevers.

The goal for some of these efforts is to genetically alter the disease-spreading insects, while other efforts seek to manipulate organisms that live within the bugs. It will take a lot of basic scientific research before a single infection can be prevented. But even if researchers can develop genetic approaches to preventing infections, they'll face another, perhaps tougher, challenge. Will governments permit the release of modified insects or bacteria, even in regions of the world where they might do the most good?

While nobody plans to release mutant insects or microbes for at least several years, recent progress has transformed fanciful visions of doing so into feasible projects.

RESILIENT SCOURGES In the mid-20th century, insecticides and other measures eliminated malaria from the United States and Europe, and many public health workers were optimistic that spraying chemicals could greatly reduce the global burden of many vectorborne diseases.

In retrospect, says Frank H. Collins of the University of Notre Dame in Indiana, "it was a little bit naive to think of it that way." Many insect populations, particularly in tropical regions, proved too hardy. Chagas' disease, once nearly eliminated from the southern reaches of South America, is making a comeback there. Dengue fever and yellow fever, both spread by mosquitoes, occur more widely and with more frequency today than they have in recent decades.

"We've conceded that we're not really going to get rid of the mosquitoes," says molecular biologist Anthony James of the University of California, Irvine. But augmenting conventional measures with genetic engineering and other innovative approaches might pare down some vector populations and leave others incapable of spreading sickness, he says. …