Scientists are stepping up their efforts to eradicate sleeping sickness across sub-Saharan Africa.

This potentially deadly condition affects more than 500,000 people each year. Four out of five people who contract it die.

The disease is caused by the trypanosomiasis parasite and is transmitted by the tsetse fly.

The disease if not treated can cause death Eric Fevre, University of Edinburgh

These parasites are found in as many as one in three cows in some parts of the continent.

"Infected animals look very thin and they lose appetite," says Subhash Morzaria of the International Livestock Research Institute (ILRI) in Kenya. "About 99% of animals if not treated will die."

Traditionally, experts have advised farmers to treat infected cows with drugs or insecticides However, these are expensive and out of the reach of many.

There is also increasing evidence that fly trapping, which is carried out extensively in a bid to combat the disease, is ineffective.

New approaches

As a result, scientists at the ILRI are looking at alternative approaches.

One of the options being considered is to try to breed cattle that are resistant to these parasites.

The scientists already have a head start because Ndama cattle are naturally resistant.

However, these cows grow slowly and are small which means they are not particularly popular with farmers.

The scientists are hoping to cross-breed these cows with Boran cattle which are more beefy and more popular with farmers.

It is a long-term project but the scientists believe it is the way forward.

"Cattle are major reservoirs for parasites that infect humans," says John McDermott, a vet and epidemiologist at the ILRI.

"There is a great interest in reintroducing cattle in many areas but the risk is that if we reintroduce cattle that are infected with this parasite then the disease will spread."

He adds: "Recently in Uganda, that was exactly the case. Sleeping sickness has been spreading from cattle over whole districts at a rate of 1.5km per month."

Vaccine hope

Their efforts are important because there is also little hope of a vaccine to protect cows from the parasites within the next few years, not least because the African market is too small to entice pharmaceutical industries to invest in research. Other options are also being considered.

"We are working together with policy makers and government to consider how best to treat animals before they move and avoid moving infected animals into new areas," says Mr McDermott.

Sleeping sickness can have a devastating impact on communities.

Eric Fevre of the University of Edinburgh says: "It is a significant burden because the disease is very debilitating. It is also very expensive to treat and has a huge impact on health services.

"The disease if not treated can cause death. The impact is very substantial."

This story is featured in the radio programme Health Matters on the BBC World Service.

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