In Venezuela, a mysterious disease has killed nearly 40 people from indigenous river communities. In one village, 10% of the population has died. James Ingham investigates.
The origin of their name is not known for sure, but the Warao are often referred to as the "boat people".
The Warao's remoteness makes seeking medical help very difficult
Venezuela's second biggest indigenous group live on the banks of the mighty River Orinoco.
It is impossible not to be impressed by the landscape here.
There is just so much water. The hundreds of tributaries and channels spill with wildlife.
A chorus of birds, frogs and monkeys fills the air. River dolphins break the surface, splashing through the brown water as it flows through long grassland and forests to the sea.
This is a beautiful and largely unspoilt area.
But it is this isolation that also makes life so hard for the Warao. These people have few material goods aside from the basic huts they live in. Theirs is a hand to mouth existence.
They get by, but, when illness strikes, they struggle and suffer.
The child mortality rate is high. Poor nutrition and hygiene and inadequate health care means simple preventable problems, like diarrhoea and respiratory infections, claim the lives of many infants.
Now, in some communities, something else is killing them.
I met up with Charles Briggs, a professor of anthropology at the University of California at Berkeley and his wife Clara, a Venezuelan doctor.
Both have spent many years living and working with rural communities here, enough time for Charles to become fluent in Warao. They both know the Delta well, and care for and respect its people.
Clara (l) and Charles Briggs (r) have been investigating the deaths
Over the past few months, they have been helping the locals devise a new health plan.
Their work changed though, when it became apparent that something was bothering these communities. A number of deaths that no one could explain.
"They asked us to help," said Charles. "So we spoke to every family that was affected in just a part of the Delta.
"Gradually a pattern started to appear. Thirty-eight people had all died in the same way".
Clara recognised some of the symptoms.
The patients had high fevers, they were partially paralysed, thick saliva was coming from their mouths and they could not drink. Some even feared water.
"We thought it must be rabies," she said, explaining that some of the patients had been bitten by bats, carriers of this killer disease.
Together with community leaders, the team wrote up their findings and began a long journey to the capital, Caracas.
At first they were refused access to a minister, but they persisted and eventually presented their findings to the government.
It was not the first time.
The Waraos had told health authorities before, that they thought something strange was going on, but they say they did not get much response. This time was different.
The government set up a commission to investigate, heading to the Delta with a boat load of experts.
After its tour of the region, the health ministry announced that it had found no evidence of rabies.
"There hasn't been rabies in the Delta for 20 years," it said in a statement without giving more information on the scope or nature of its inquiries. "But we are still trying to find the cause of these deaths" it said.
So if rabies is not to blame then what is?
Well that is a question that Odilia Torres among others wants answered. This young mother has the most tragic of stories.
The unknown disease killed three of Odilia's children
Her face shows the pain she has been through. How could it not?
In just six months, three of her four children died of these same lethal symptoms.
Nothing could stop their rapid deaths. No Western medicines, no traditional Warao medicines.
"I'm so scared," she told me, fighting back tears. "What is this sickness?"
I could see the fear and helplessness in her eyes. "I'm left with only one young child now," she said, "I'm really scared of losing her too."
More parents share similar stories.
Anita Rivas and Arcenio Torres are just beginning to grieve. They appeared numb and still in shock, as they explained how their 19-year-old daughter, Elbia, died just a few days after her husband.
"No-one has come to visit us," Arcenio told me. "We've suffered so much and now we need support. We need at least cloth to make mosquito nets, but so far nothing."
These deaths could well continue, until experts find out what is happening. But even if they do, there is still so much more that needs to be done here to ensure the Warao's health improves.
"Health conditions here are abysmal," Charles the anthropologist tells me.
"There are fundamental needs that aren't being met. We're hopeful for improvement."
The government denies it is ignoring their needs, and says a health plan is in place for the Delta.
But it is clear improvements can and must be made.
Health centres are very basic. One I visited was staffed by just a couple of local nurses backed up, sometimes, by student doctors from Caracas.
It takes these people at least a day to get to a hospital if they are lucky enough to have a motorboat, or can beg someone who does to take them.
From Our Own Correspondent was broadcast on Thursday, 25 September, 2008 at 1100 BST on BBC Radio 4. Please check the programme schedules for World Service transmission times.