KACNGUAN, Sudan -- Martha Halim lives in fear. She is terrified of the moon's phases, afraid of eating and fearful of fires, rivers and ponds.
She is stricken with mysterious seizures that frighten her from eating. Her parents have tried everything. She's been to a hospital, she's seen a Western doctor and she's taken anti-epileptic drugs.
The 13-year-old has even been to witch doctors. She followed the advice of one, crawling through a termite mound while her parents slit the throat of a goat.
She gives a grim description of what it's like when her disease overpowers her.
"When it comes, it looks like a black cloud but in the shape of a human," said Martha. "That's all I know. At the end, I find myself on the floor."
Martha suffers from a strange affliction called "nodding syndrome," apparently unique to southern Sudan. Its young victims tend to nod vigorously at the sight of food. The condition often progresses to severe seizures, mental retardation and death.
Martha fell into a fire last year when she had a seizure while cooking. Her right leg is disfigured by a severe burn from knee to foot; she protected it with a soiled beige rag.
Her father, Neen Majak, says he has nearly given up hope. Anti-epileptic drugs haven't helped and neither have the remedies of witch doctors.
The affliction, which has been found in about 300 children so far, baffles experts. The World Health Organization began investigating it about two years ago, around a year after Martha's symptom first appeared.
Peter Spencer, an American neurotoxicologist who has investigated the condition for WHO, encountered another 13-year-old girl with a bizarre variation of the illness.
"I was able to demonstrate with her that she was a regular nodder with local food and by contrast she did not nod when eating a variety of American food -- candy bars or whatever. It was absolutely staggering," he said.
As she sits on a sisal mat with her parents under the shade of a tree beside their mud huts, Martha says no treatment has helped her.
Experts say a few children recover. Doctors with WHO think the disease may be related to a disorder seen in Uganda called Nakalanga syndrome, which also has symptoms of convulsions, stunted growth and sometimes nodding.
Spencer's investigation has found no obvious environmental causes. He wouldn't rule out a food connection, but said it is unlikely.
Unraveling the mystery of nodding syndrome is a question of money and time, Spencer said.
"If we're smart, we will unravel it. We won't let it burn on like we did HIV," he said. "You just cannot imagine a greater disaster for a community than their children being hit in this way."