PADER DISTRICT, Uganda (Reuters) - Most mornings, Michael Odongkara takes his daughter Nancy Lamwaka outside and ties her ankle to a mango tree.
It's not something he likes to do. But the disease that gives the 12-year-old violent seizures has so diminished her mental capacity that she no longer talks and often wanders off. Once, she was lost in the bush for three days.
"It hurts me so much to tie my own daughter to a tree ... but because I want to save her life, I am forced to. I don't want her to (get) loose and die in a fire, or walk and get lost in the bushes, or even drown in the nearby swamps," he said.
Lamwaka suffers from nodding syndrome, a disease of unknown origins and no known cure, which Ugandan authorities estimate affects more than 3,000 children in the country.
Named after its seizure-like episodes of head nodding, the disease, which mostly affects children between five and 15, has killed more than 200 children in Uganda in the past three years. Thousands of children in South Sudan are also sufferers.
As the seizures are often triggered by food, children who have nodding syndrome become undernourished and mentally and physically stunted.
"There is a general effect on their neurological system to the extent that some can be impaired in vision, eating and even mere recognition of their immediate environment," said Dr. Emmanuel Tenywa, a country advisor in disease control for the World Health Organization (WHO) in Uganda.
As her father watched helplessly from under a nearby tree, Lamwaka cried out and began to convulse. Saliva flowed from her mouth and her whole body shook for a few minutes until she finally went limp in the dust. Lamwaka has had episodes like this up to five times a day for the past eight years, and her health has steadily deteriorated.
"When she was talking she would ask for food," he said. "These days she just stretches out her hand begging for it."
Nodding syndrome was first documented in Tanzania as early as 1962. Fifty years later, researchers still don't know what it is.
"We have a long list of things that are not causing nodding disease. We still don't have a definitive cause," said Dr. Scott Dowell, director of the division of global disease detection and emergency response of the Centers for Disease Control (CDC).
Officials from the Atlanta, Georgia-based CDC were in Uganda for nine days in February on the latest of three trips to investigate the disease.
"We have ruled out, through our field studies and our laboratory testing, more than three different hypothesized causes including . . . 18 virus families with hundreds of members," said Dowell.
It's a relatively rare situation for the CDC to be in; of 600 outbreaks of illnesses investigated by the organization's division of global disease detection, just six are unresolved.
Although they have no reason to believe the disease will spread, researchers can never be certain. Dowell cites "slim disease," which emerged in West Africa in the 1980s and turned out to be the beginnings of AIDs.
The researchers do have some leads: one is a possible link with the black fly-borne parasite that causes river blindness, or onchocerciasis.
"All of these cases are reported in areas where there is onchocerciasis, so we strongly think there is a relationship between the two," said Dr. Tenywa of the WHO.
Investigators say they plan to do genetic testing on skin samples taken from the children to try to establish a link.
"In the coming weeks we anticipate learning a lot more about whether this is a variant of onchocerciasis or whether it might be some other sort of parasite that looks like onchocerciasis," said the CDC's Dowell.
Researchers have also observed a deficiency of vitamin B6 in the populations where the disease is prevalent.
As long as the cause of the disease remains unknown, officials are focusing on treating its symptoms. CDC researchers met with Ugandan health officials to discuss how a trial of treatments would work.
The trial, which could begin as early as May, will test two types of anti-convulsants as well as vitamin B6 supplements. Some afflicted children are already on anti-epileptic drugs, with varying degrees of success.
"I think everybody is in agreement that at this stage it would be good to have a much better idea about what treatments are working and if any of them are harmful," Dowell said.
Investigators say that they hope to have a protocol for the trial, which will include 80 children, ready to submit for ethics approval in Uganda and the United States in a couple of weeks.
But for those who have been living with the disease and its effects, it all seems to be moving very slowly. In Uganda, frustration over the government response is growing.
"People are very bitter and they think the government has abandoned them," said Martin Ojara, local council coordinator for the Acholi sub-region in Uganda, which is where the disease is concentrated.
Though the government recently announced a plan to establish treatment centers and bring in health workers to address the disease, some say it's too little, too late.
A request by the Health Ministry for 3.8 billion Ugandan Shillings (about $1.5 million) to fight the disease was not included in the supplementary budget recently submitted to parliament for approval. The finance ministry, which said the request was late, has instructed health authorities to reallocate funds from their existing budget until the next supplementary budget.
"It is very sad," said Beatrice Anywar, an opposition member of parliament for one of the most affected areas. "It shows how the government really doesn't care."
The government maintains it has been seeking a cause and treatment for the disease since it first surfaced.
"There have been a lot of attempts, from 2009 to date, to get the riddle of this situation answered -- what is the problem and how can it be addressed," Musa Ecweru, the minister of state for disaster preparedness and emergency response in the prime minister's office, told reporters in early March.
"Everybody knows that government has not just folded its hands. It has been doing all it takes to make sure that it will (get) on top of this situation," he said.
Anywar and others have called for the area to be declared a disaster zone -- in some villages in her district, almost every family has a child with nodding disease and some families even have several, she said.
"The children (with the disease) who are of school-going age cannot go to school and have no future," said Anywar. "Food security is a problem because these parents are not productive.
"The parents of these sick children are traumatised by an unknown disease and literally have lost hope."
Children with nodding syndrome are prone to accidents such as drowning and burning because of mental impairment, and many of the fatalities from the disease are the result of these secondary causes.
Since she contracted the disease, Lamwaka has had many such incidents. Her body is covered with bruises from falling and there are raw, pink wounds on her hands from when she fell into the fire recently when both of her parents were away.
"She doesn't know that she is on fire, that she is burning until someone comes and brings her away from the fire," said her father.
He admits he has stopped taking her to the doctor.
"Even if they give us drugs, I'm not sure if the drugs will help," said Odongkara.
Sitting in the shade nearby is his mother, Jujupina Ataro, 72. She has three grandchildren with the disease and spends her time bathing and feeding them, and even cleaning up their faeces since they can no longer use the toilet by themselves.
She said many of her neighbours and friends also have children with the disease.
"I know so many in this area. If a doctor would come you would see how many people would turn up ... it's uncountable," she said. "It's like the generation is wiped out."
Editing by Sonya Hepinstall