For most people, a single bite from a parasite-infected tsetse fly can trigger a slow, agonizing and sometimes fatal disease known as African sleeping sickness. But new research shows that some people, as well as baboons and other great apes, are naturally resistant to infection. Cassandra Willyard awakens to the possibility of using existing immunity to engineer new therapies and transgenic livestock.

Jayne Raper, her long brown hair swept back into a bun, leans forward to look through the twin lenses of a benchtop microscope. The slide below them contains hundreds of wriggling parasites. These are African trypanosomes—not the variety that causes sleeping sickness in people, but a very close cousin that infects cattle and other animals. These single-celled protozoans just came out of the freezer, but the microscope’s hot light makes their knife-like bodies thrash and twist. “They’re beautiful, aren’t they?” she muses.

‘Beautiful’ may not be a word that most researchers would use to describe this deadly parasite. But Raper, a biochemist at New York University School of Medicine, is mesmerized by the microbe and the possibility of thwarting its defenses to combat sleeping sickness, a plague that afflicts an estimated 30,000 people living in Africa each year. Over the past two decades, Raper and other basic scientists have learned an astonishing amount about how this tiny organism evades the human immune system, and they have uncovered genetic mutations that allow humans and other primates to resist the parasite. Yet it is still unclear whether they can leverage their newfound knowledge to curb the disease.

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