Tackling sleeping sickness from within.

Throughout sub-Saharan Africa, the tsetse fly is the bearer of bad news. When it feeds, this blood-sucking insect can transmit parasites called trypanosomes into humans. The parasites cause sleeping sickness, a disease that attacks the nervous system and can lead to death.

Trypanosomes aren't the only guests residing inside tsetse flies. Several kinds of bacteria also have symbiotic relationships with the flies, notes Serap Aksoy of Yale University School of Medicine. The insects provide organelles that comfortably house the bacteria; in return, the microorganisms synthesize compounds that supplement the tsetse fly's limited diet.

Aksoy and her coworkers have recently learned how to maintain a population of one of these bacteria in the laboratory, an ability that has enabled the researchers to add foreign DNA to the microbes. The genetically engineered bacteria can still live symbiotically with tsetse flies. Aksoy plans to modify the bacteria by adding genes that encode trypanosome- destroying compounds. If researchers can spread such bacteria through the tsetse fly population, they might rid the insects of the disease-causing parasites, says Aksoy.