Sleeping sickness test 'promising'

Sleeping sickness is a big killer in rural Africa

A genetic test for cattle could have an impact on the control of sleeping sickness, which claims the lives of about 100,000 people in Africa every year.

Scientists at the University of Edinburgh have been looking at the genetic structure of the parasites which carry the disease and can be transmitted to humans by tsetse flies.

It is hoped their discovery may lead to the development of a simple diagnostic test to check which cattle are carrying the dangerous parasites in east Africa.

Livestock there are hosts to two sleeping sickness parasites - Trypanosoma brucei rhodesiense, which affects humans, and Trypanosoma brucei brucei, which is non-human-infective.

The disease is spread by the tsetse fly

Up until now, scientists have been unable to differentiate between the two under the microscope because they look so similar.

But in a fast-track study in Uganda, the team of researchers made an important discovery, which is published in The Lancet.

They tested 70 T brucei samples, collected from humans and cattle in Uganda, for the presence of the serum-resistance-associated (SRA) gene, which allows Tb rhodesiense to survive in human serum.

SRA was present in all 29 samples from patients with sleeping sickness and in all eight cattle samples that were resistant to human serum in vitro.

Drug treatments

The gene was not found in any of the 33 cattle samples that were susceptible to human serum.

The team believes the presence of the SRA gene in cattle blood indicates they are carrying the Tb rhodesiense parasite, which could affect humans in east Africa.

Sue Welburn, who led the team carrying out the research, said: "Detection of the SRA gene could provide the basis of a simple diagnostic test to enable targeted control of Tb rhodesiense in the domestic livestock reservoir, thereby reducing the public-health burden of sleeping sickness in east Africa."

If the team have 100% correlation it sounds at least promising as a diagnostic test

Dr David Horn, microbiologist

Cattle found to be carrying the human-infective parasite would be treated with drugs to eradicate them from the animals' bloodstream.

Dr David Horn, a microbiologist at the London School of Hygiene and Tropical Medicine, believes this is a significant discovery.

He said: "If the team have 100% correlation it sounds at least promising as a diagnostic test.

"It seems quite impressive."

Preventing the spread of the disease has focused on eliminating tsetse flies in east Africa, but this is only a temporary solution.

Sleeping sickness is almost always fatal, although drugs are used to treat the disease.

Drug treatment can be associated with severe side-effects and up to 5% of people die as a result of chemotherapy.

A diagnostic test would make it easier to control the spread of the disease, say scientists.