A trio of instruments for tsetse control
Africa may be the birthplace of humanity but for hundreds of thousands of years, human activity on the continent has been constrained by unpredictable climates, harsh environments, pests and more disease-causing parasites than exist anywhere else in the world. Whilst the hundreds of migrants that were the first to leave Africa dispersed, thrived and multiplied, those that remained behind continued to struggle to survive. Over the millennia many parasites, including malaria and bilharzia, have affected people's potential to prosper but one insect pest - the tsetse (Glossina Spp.) - and the parasite it carries has, above all, limited the land available for cultivation and the spread of domesticated livestock. Despite many and various approaches to its control over the past 100 years, tsetse remains unchanged and the affect of the trypanosome species that it transmits continues to affect millions of poor people and their livestock. The challenge today, according to Ian Maudlin, Programme Manager for the DFID Animal Health Programme, is to provide tools for the individual farmer so he can deal with the problem of tsetse and trypanosomiasis in his own way and in his own time.
During the past year there has been some healing of the divisions within the international tsetse and trypanosomiasis community on the best way forward for tsetse control, and it is clear that future disease management strategies should encompass a broad range of control options for use in different circumstances. One tool will not fit all. With this in mind, recent advances in several livestock keeper-based tsetse control strategies were discussed at a workshop held in Nairobi in October 2003 with the aim of taking new knowledge in each area to a point where promotion and application of each of three technologies could be realised.
Restricted application: a reason for restraint?
One of the best-known techniques of farmer-based control of tsetse is the application of insecticides - pyrethroids - to cattle. However, the method of application has generally involved 'whole body' treatments applied at monthly intervals, which can prove expensive or require a plentiful and guaranteed supply of water. Additional concerns from researchers include the effect on dung beetles due to the contamination of dung, and the impact on tick populations, which can prevent young cattle from developing a natural immunity to tick-borne diseases. From research in Zimbabwe, the solution seems to lie in the restricted amount of insecticide used on each animal and, in theory, it appears that not all animals need to be treated. For G. pallipides, it has been found that the flies mainly feed on the belly and the legs of cattle. By minimising treatment to these areas, application intervals can be doubled and yet total insecticide use, compared to whole body applications, can be reduced to around 40 per cent.
The advantage with this technique is that existing formulations of pyrethroids can still be used and applied by the farmer with existing equipment, be it a paintbrush or sprayer. The current limitation of the technology is that is has only been tested in Zimbabwe and only on G. pallipides although collaboration has begun on tests in other regions with other species of tsetse. As Glyn Vale of Natural Resources Institute (NRI) in the UK, concludes, "This is not a new idea. In fact many people are already using restricted application for ticks but we are simply trying to point out that with a slight tweaking of the application, farmers could save an enormous amount of money and still get good control of tsetse."
A net advantage for zero-grazing
Small-scale farmers produce the majority of Kenya's milk but, many of the cows are kept in zero-grazing pens where they are a sitting target for biting flies, including tsetse. And, if animals become infected with trypanosomosis, milk yields, calving rates and farmers' incomes are seriously affected. To improve livestock production in Western Kenya, an EU Project known as FITCA (Farming in Tsetse Controlled Areas), has been testing an insecticide-impregnated net which is used as a one-metre high barrier around the pen to prevent biting flies from bothering the cows. The effects, according to Burkhard Bauer, Project Manager for FITCA in Kenya, have been quite remarkable.
Cows bothered by biting flies are constantly on the move, stamping their legs, swishing their tails and twitching their ears, which can make milking difficult and inhibit proper let-down of milk. Even without the presence of disease, milk yields can be extremely poor, as little as one litre per milking. However, with an insecticide-treated barrier to prevent the flies from entering the pen, cows quickly settle and farmers are reporting improved milk yields of up to day 2 to 3 litres a day. Other observations include fewer flies around the compound, including mosquitoes affecting the household. Much interest in the technology has already been evident from farmers not involved in the project. It is hoped that this interest will continue to spread, and a private company that has taken up the approach is currently working on a distribution network to make the polyester netting commercially available.
A harmonious approach
What is it about a warthog that makes it so attractive to tsetse and yet waterbuck and zebra remain free of the effects of tsetse and the trypanosomes they carry? The answer, according to Rajinder Saini of ICIPE (the International Centre for Insect Physiology and Ecology, Kenya), is an odorous one: warthogs have a smell that attracts or 'pulls' tsetse to them whereas the smell of a waterbuck repels or 'pushes' tsetse away. Although cattle are also highly attractive to tsetse, it has been known for some time that cattle urine contains one compound, methoxyphenyl, which is mildly repellent. This has been used by ICIPE to develop a synthetic repellent, which effectively prevents tsetse from smelling the cattle when hung in a dispenser on a collar around the animal's neck.
Trials have been conducted on herds in Nguruman in south-western Kenya with pastoralist herds and results have shown that with only 50 to 75 per cent of the animals wearing collars, over 95 per cent of the infection occurs in unprotected animals. Although the compound is only currently available in minute quantities, which makes it very expensive, an agreement has already been signed with an Italian pharmaceutical company to start mass-production. For pastoralists, who currently rely on trypanocidal drugs for trypanosomiasis control, it is an alternative option, which can be used alone to push tsetse away. For more sedentary communities, the use of the collar ('push') could also be combined with a 'pull' technology, that is cattle treated with pour-ons or with traps/targets in the area where protected cattle are grazing ('pull and kill').
From a researcher's point of view each of the three technologies will continue to be tested and refined. But for farmers anxious to protect their cattle any one of these approaches, all of which have proved to be effective and simple to use, could be used without further discussion. However, the difficulty of technology transfer in Africa is not only whether these tools are commercially viable but that Africa's range of climates, habitats, pests and diseases means that each technology will have to prove itself against the continent's diversity if they are to be truly successful against tsetse.
Date published: January 2004
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