20100405
ALLAFRICA

Lagos — A powerful lure to trap and kill the tsetse flies that transmit sleeping sickness in humans is one step closer following the identification of the scents that attract them.

Using either artificial or natural scents to bait tsetse fly traps is not a new idea. They are already used to attract flies that carry parasites that cause sleeping sickness in animals.

But scientists had been unable to identify the scents that lure the flies that carry the sickness. Now research in Burkina Faso and Ivory Coast has found chemicals in human odours, as well as those from cows and pigs that lure more flies towards traps.

Tsetse flies infest about ten million square kilometres of Sub-Saharan Africa, where they transmit parasites known as trypanosomes that cause human and animal African trypanosomiasis.

There are no vaccines or prophylactic drugs for the disease. It is treated with drugs to which the parasites are becoming increasingly resistant, and can have unpleasant and sometimes fatal side effects.

The only option for tackling the disease is killing flies using traps. This could be more effective if they were baited with odours, said the researchers writing in PLoS Neglected Tropical Diseases. This would then reduce the number of traps needed and therefore cut costs.

"We are trying to identify attractants for the species that cause sleeping sickness in humans, and so help to make the control devices more cost-effective," co-author Michael Lehane, of the Liverpool School of Tropical Medicine, United Kingdom, told SciDev.Net.

In West Africa, the most dangerous tsetse fly species belong to the river dwelling palpalis group -in Burkina Faso, Glossina tachinoides and Glossina palpalis gambiensis; and in the Ivory Coast, Glossina palpalis palpalis.

The researchers found that G. tachinoides is attracted to cow odour; G. P. gambiensis to cow and human odour; and G. P. palpalis to odours from pigs and humans.

In some cases the attraction rates soared - for example, traps baited with cow odour attracted five times the number of G. tachinoides flies.

"Our results showed that attractants can improve trap catches up to three fold for tsetse of the palpalis group. This is new for this group and will make tsetse control cost effective by reducing the number of traps and targets deployed," said Jean Baptiste-Rayaisse, the paper's lead author, from the International Centre of Research and Development on Breeding in Sub-Humid Areas (CIRDES) in Burkina Faso.

Lehane says that the researchers are aiming to test the technology in the field in the near future.