Existing targets for tsetse flies are bigger, and so more expensive, than the new targets

Wikipedia/Rob Merkus

[CAPE TOWN] The mammoth task of controlling tsetse flies, which spread sleeping sickness, in Sub-Saharan Africa could be made cheaper with the development of a more efficient insecticide-treated trap.

Some types of tsetse fly can be caught with traps that use artificial odours to lure them in. But Glossina fuscipes flies, which cause more than 90 per cent of sleeping sickness cases, are not attracted to artificial odours, and the natural odours that attract them have not yet been made into baits (see Tsetse flies lured by lizard scent).

Instead, control methods rely on traps or insecticide-treated targets without odour baits, but these must be widely distributed, making them costly and laborious to use.

In studies at Lake Victoria in Kenya, published in PLoS Neglected Tropical Diseases this month (7 July), scientists tried numerous types of insecticide-treated targets — netting injected with insecticides — to kill the flies.

They found that a small target covered in blue-and-black cloth attracted and trapped more tsetse flies than existing methods. It was also found to be cheaper.

Using the right colour means that the size of the targets can be reduced from one square metre to just 25 square centimetres. Twice as many are needed, but the cost per target is much smaller, say the researchers.

"The cost-effectiveness of the targets has been improved," says Jenny Lindh, an author of the study, who works at the UK-based Liverpool School of Tropical Medicine.

The scientists are now developing better visual baits, Lindh told SciDev.Net.

Setting so many traps can be problematic, says Glyn Vale, Zimbabwean-based adviser to the South African Centre for Epidemiological Modelling and Analysis at Stellenbosch University in South Africa. "There are the challenges of weather conditions, wild animals and people that might interfere with your work but the study has been aided by a great team of Kenyan researchers," he says.

Sleeping sickness affects around 300,000 people every year in Africa. The disease, caused by trypanosome parasites transmitted by the tsetse fly, can be treated only with toxic drugs that are hard to administer and sometimes ineffective.

If tsetse fly control becomes more effective, the demand for such drugs should decline, says Vale.

Link to full paper in PLoS Neglected Tropical Diseases