In the middle of the West African rainforest a unique research project is underway.

1996-7 saw 280 ebola deaths

High up in the tree canopy scientists are trying to find the source of one of the world's deadliest diseases before another major outbreak occurs.

The disease is ebola and the next six months may prove crucial for the scientists' quest.

In the middle of the night deep in the forest of Ivory Coast, scientists test the blood of a bat in the hunt for one of the world's deadliest viruses.

Gareth Jones at a laboratory station deep in the Ivory Coast jungle

The type of bat they are testing may be the host for ebola virus - cause of one of the most frightening diseases known to science.

In 1995 a single ebola outbreak killed 245 in the town of Kikwit, in former Zaire.

It has one of the highest mortality rates of any disease, with at least four out of five of those infected bleeding to death. Since 1976 there have been nine major ebola incidents - scientists urgently need to know more about it.

Scientists have had only 20 years to study the mysterious virus but it is probably been lurking in the African jungle for millions of years. But where exactly is the natural reservoir and why is it apparently breaking out more often now?

Dr Pierre Formenty is one of several international virus hunters trying to find out. The World Health Organization has built an arial walkway high up in the rainforest of Ivory Coast close to the site of an ebola outbreak in chimpanzees four years ago.

Every day in the rainy season Dr Formenty sets traps for animals suspected of hosting the virus. Scientists are narrowing the hunt down to the forest canopy and believe they are getting closer.

It is thought that humans get ebola by coming into contact with infected chimpanzees or monkeys. But researchers think its origins lie further down the food chain - in plants, small mammals or insects.

Having trapped the animals, the dangerous work at the forest research station now begins. When a virologist handles anything with suspected ebola, the most stringent precautions are needed. A Swiss scientist dissecting a chimp in 1994 contracted the virus and almost died.

Bats are thought to be a principal carrier

"We try to take precautions to prevent any outbreak," said Dr Formenty.

"One of these animals may have ebola. If you forget to be attentive in your work it could be deadly for you."

So far 1,800 mammals and 300 birds have been tested and all shown up negative for the virus.

That leaves Dr Formenty homing in on his chief suspects - bats. He says that catching them in the forest canopy has revealed how little we know about these animals. But it will be another six months before tests become sophisticated enough to prove if they are indeed the hosts.

If so, more research on their behaviour will be needed to try to predict the next outbreak.

As human populations encroach further into the rainforest in search of food, fuel and land, such research is vital. And not just on ebola, but on the increasing number of strange viruses with which humans are now coming into contact.

Working with the virus is extremely hazardous

There is concern that with rapid changes in climate and ecology, we will be threatened by dangerous new viruses or new combinations of them

"Viruses are now taking advantage of each other to cause damage to human populations," says Dr Formenty.

The experts behind this project are deeply concerned about emerging viruses. In the past 20 years 30 new diseases have been reported - many of them spreading from animals to humans.