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Scientists believe they have found a way to beat sleeping sickness using a bacterium against the tsetse fly host that spreads the disease to humans.

In the same way that we have friendly bacteria in our intestines, the tsetse fly harbours bacteria in its midgut, muscle and salivary glands.

Experts in Belgium have genetically modified these "good bugs" so they attack the culprit parasite carried by the fly.

But work is needed to hone the process.

The latest findings are published in the open access journal Microbial Cell Factories.

Sleeping sickness, or human African trypanosomiasis, is a potentially fatal disease that plagues many regions of Africa.

Although the number of people being infected with the disease has been going down thanks to better diagnosis and treatment, there were still more than 7,000 new cases recorded in 2010.

The parasite causing sleeping sickness is transmitted to humans through the bite of the infected tsetse fly.

This causes fever, headaches, aching joints and itching. Then follows the second stage of disease as the parasites cross the blood-brain barrier to infect the central nervous system.

The person then becomes confused, poorly co-ordinated and experiences the sleep disturbances which give the disease its name.

Without treatment, sleeping sickness is fatal.

But current therapies often have unpleasant side-effects.

The drug most commonly used to treat the condition is a derivative of arsenic developed more than 50 years ago. And the treatment can be excruciatingly painful and potentially fatal. Often described by patients as "fire in the veins," between 5% and 20% of those treated die of complications from the injected drug.

And so scientists are seeking alternatives.

The Belgium team at the Institute of Tropical Medicine in Antwerp have focused on finding a way to destroy the sleeping sickness parasite - trypanosome - that the tsetse fly carries.

They found bacteria called Sodalis glossinidius, which naturally live in the fly and can be used to mount an attack from the inside.

Altering the genes of the bacteria led it to release fragments of antibodies known as nanobodies against the parasite.

With more work, the researchers hope to be able to produce targeted nanobodies which could kill or block the development of trypanosome.

Dr David Horn of the London School of Hygiene and Tropical Medicine said: "This is a neat and promising concept. The goal now will be to develop a deliverable toxin, not necessarily a nanobody, which exhibits anti-trypanosomal activity in the fly."