The village of Tumangu, in northern Uganda, defines remote. It's hard even to find on maps. But it shows up frequently in news stories. Grace Aber is about to show me why.
She leads me down a narrow dirt path, passing a couple of clay huts. We get to a big mango tree. Aber's 17-year-old son, Patrick, sits under it. His shoulders are slouched. His eyes look like glass.
Aber tries to get him to say his name. A small grunt is the only sound he makes.
Patrick wasn't always like this, Aber says. He used to love going to school, reading. But a decade ago, when he was about 6, he began to change.
"It started with the nodding of the head," Aber recalls.
First the nodding, then seizures, with Patrick writhing on the ground, screaming.
Aber didn't know that what she was witnessing was the onset of what is known as nodding syndrome, a strange and debilitating illness that affects only children in a small pocket of East Africa. Its cause is unknown.
Patrick's convulsions continued a few times a day, every day. He stopped growing. He stopped talking.
And then, a year later, Aber noticed Patrick's little sister, Amiro Alice, stumbling around. A few days later, Aber realized that Alice was also nodding. A couple of years later, a third child. Then a fourth.
"My heart was scared. How does this disease catch someone?" she asks. "We want researchers to tell us the ways that someone catches this disease."
Scott Dowell, with the Centers for Disease Control and Prevention in Atlanta, is leading its investigation into nodding syndrome. Usually, he says, investigators can figure out the cause of a strange outbreak after just a few weeks. This hasn't been the case here.
"Nodding syndrome is definitely unusual in that it's a much tougher nut to crack," he says.
For more than three years, epidemiologists at the CDC have been trying to crack it. They've gone to northern Uganda and collected blood samples, tissue samples, spinal fluid. Dowell says they've looked at all the infectious causes that CDC can test for, but the explanation is still not clear.