20100122
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Nairobi — Scientists baffled by the continued spread of sleeping sickness through Uganda have discovered that it is livestock markets that are driving the disease.

A team from Uganda and the United Kingdom analysed the incidence of the serious Rhodesian form of sleeping sickness, which is carried by cattle, in two newly affected districts.

They confirmed that villages close to livestock markets have higher rates of the disease.

The team looked at nearly 700 villages in the two districts. The scientists calculated the vulnerability of a village to sleeping sickness by mapping how close it was various risk factors such as areas where tsetse flies - which transmit the disease - are likely to live, livestock markets and health facilities.

They found that for every kilometre further from a livestock market a village was, the chance of catching sleeping sickness reduced by 21 per cent.

The research shows that livestock markets are a "major risk" to disease control, Sue Welburn, professor of medical and veterinary molecular epidemiology at the University of Edinburgh in the UK, and co-author of the research, told SciDev.Net.

There are two forms of sleeping sickness, or African trypanosomiasis - the Rhodesian form, common in eastern Sub-Saharan Africa, and the Gambian form which affects western and central Africa.

Uganda has caused particular concern because the country experiences both forms. In 2005, a British Medical Journal paper - also co-authored by Welburn - warned that the Rhodesian form was spreading northwards, posing the risk of convergence (see Double parasite threat of sleeping sickness in Uganda).

"The diseases have been separate for over 100 years but with expanding cattle trade northwards Rhodesian sleeping sickness has been moved northwards," Welburn explained.

She added that because diagnosis and treatment of the two forms are so different, treatment could be compromised - with patients receiving the wrong drugs for example - if the diseases coexisted.

To prevent the convergence, said Joseph Maitima, a senior scientist with the Kenya-based International Livestock Research Institute (ILRI), it is necessary to restrain each of the two in the areas they are endemic to by treating livestock before they are moved for sale or for pastures.

In response to the 2005 findings, a campaign - Stamp Out Sleeping Sickness - was launched. Cattle were treated and transmission was reduced by 75 per cent, diminishing fears of a deadly convergence. But villages are still being infected.

"The disease has stopped moving, but we are still having outbreaks because infected animals are not being treated as they should be," said Welburn.

The Stamp Out Sleeping Sickness programme will continue in February to treat all cattle in the two new regions to which it has spread.

The research was published in PLoS Neglected Tropical Diseases last month (December).