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Maria Teresa Segundo remembers thinking the deaths were normal. Her grandparents and older neighbors would suddenly see swelling in their knees or wrists. They’d be very tired. And then, one day, they’d be gone.

“We thought it was just age,” says the 50-year-old woman from the Guarani ethnic group, who has the loose skin and shrinking body of someone decades older. Then, in the 1990s, the Bolivian government began reaching out to communities to explain that the deaths were being caused by a disease called Chagas, which is transmitted by a bug called the vinchuca. This pest, known in the U.S. as the “kissing bug,” lives in the walls of mud huts in the eastern Bolivian region known as the Chaco and elsewhere. The beetlelike insect feeds off of the blood of animals and people.

Chagas is a disease that can lay dormant for years, eventually causing extreme fatigue and joint swelling; the lifetime risk of developing heart or other vital organ failure is about 30 percent. For decades Chagas has been endemic throughout South America. Several countries greatly reduced contagion through fumigation and by building homes of concrete, which the vinchuca can’t penetrate, but approximately 8 million people in 18 countries in the Americas still suffer from the disease.

After a visit to Segundo’s village decades ago, local government officials sprayed people’s homes with insecticides every few months, she says. She would get headaches from the smell, which lingered for days. The pests always returned.