Chagas Disease (African Trypanosomiasis)

Trypanosoma cruzi parasites in a stained blood smear — Trypanosoma cruzi parasites, the cause of Chagas disease. (Wikimedia Commons / CDC — Myron G. Schultz, public domain)

Chagas disease and African sleeping sickness are caused by closely related parasites — Trypanosoma cruzi in the Americas and Trypanosoma brucei in sub-Saharan Africa. Together they sicken millions and remain hard to cure.

Chagas disease

Chagas spreads through the "kissing bug," a nocturnal insect that lives in the cracks of mud-brick walls across Latin America. Its bite delivers the parasite into the bloodstream, where it settles in for life. About 6.5 million people are infected, mostly in Latin America, with another 300,000 in the United States.

For most of those people the infection is silent for years. Then, in roughly a third, it starts attacking the heart, the esophagus, or the colon — Chagas is one of the leading causes of heart failure in endemic regions. The two available treatments, benznidazole and nifurtimox, only work reliably when given early; in chronic patients they fail more often than they succeed, and most patients can't tolerate the side effects.

African sleeping sickness

Across sub-Saharan Africa, a cousin parasite — Trypanosoma brucei — is carried by the tsetse fly. Early infection looks like malaria: fevers, headaches, swollen lymph nodes. If untreated, the parasites cross into the brain. Sleep cycles invert, confusion sets in, and the disease becomes fatal.

Adult tsetse fly resting on a surface — Tsetse fly (Glossina morsitans), the vector for African sleeping sickness. (Wikimedia Commons / Alan R Walker, CC BY-SA 3.0)

Roughly 70 million people live in tsetse country across 37 African nations. Better surveillance has cut new infections sharply — fewer than a thousand reported in 2018 — but the existing treatments are decades old. Melarsoprol, still used for advanced cases, kills about 5% of the patients it treats.

What Folding@home simulates

Trypanosomes are single-celled organisms — many orders of magnitude too big to simulate atom-by-atom, even one of them. Folding@home simulates the proteins inside the cell instead: the molecular machines a parasite relies on to survive in its host. Mapping how one of those proteins folds and moves can reveal where a small drug-like molecule might grip it and shut the parasite down.