AN AMBITIOUS campaign to rid Africa of one of its greatest scourges, the
tsetse fly, was launched this week by African countries with the support of UN
agencies. The decision follows the successful eradication of the fly from the
island of Zanzibar.
The tsetse fly carries single-celled parasites called trypanosomes that
attack the blood and nervous system, causing sleeping sickness in humans and
nagana in cattle. Sleeping sickness kills up to 400,000 people each year, and
the tsetse鈥檚 direct and indirect effects are estimated to cost the continent
around $4 billion a year.
In Zanzibar, the first step was to cut tsetse numbers by trapping them and by
applying insecticide to the backs of cattle. Then vast numbers of males rendered
sterile by exposure to gamma radiation from cobalt-60 were released from planes
(快猫短视频, 29 November 1997, p 12).
Female tsetse only mate once,
so if their mate is sterile they don鈥檛 produce any offspring. Since Zanzibar was
declared tsetse-free in 1997, meat and dairy production have doubled.
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Now PATTEC, the Pan African Tsetse and Trypanosomiasis Eradication Campaign,
will extend the programme to the whole of Africa. 鈥淭his campaign is really
getting at the root of poverty,鈥� says Peter Salema of the International Atomic
Energy Agency in Vienna, one of the agencies supporting the campaign. For
example, tsetses have prevented the use of oxen for ploughing or, he says, for
transportation.
The PATTEC programme has been made feasible by a tenfold fall in the cost of
producing sterile males in the past decade. Tsetses are hard to breed because
they bear just five or six live young. But semi-automated systems have now been
developed for raising them, and for separating the sexes. A silicon membrane
feeding system also means the flies can be fed using blood from abattoirs
instead of live animals.
Despite this, totally eliminating the tsetse from Africa could cost as much
as $20 billion. But the campaign will build on the $35 million a
year that African governments already spend on eradication.
One complication is that whereas there was only one type of tsetse in
Zanzibar, there are 22 varieties elsewhere in Africa. Fortunately, tsetses are
poor fliers and many infested areas are isolated from each other, so the problem
can be tackled step by step.
Preparatory work is now under way in Botswana, Mali and Ethiopia. 鈥淭he
country that鈥檚 most keen is Ethiopia, and they believe they have mountain
valleys there sufficiently isolated for the fly to be eliminated,鈥� says Chris
Curtis of the London School of Hygiene and Tropical Medicine. He points out that
the sterile insect technique was used successfully to eliminate screw-worm flies
in North and Central America.
But the programme won鈥檛 be welcomed by everyone. Some regard the tsetse as
鈥淎frica鈥檚 best conservationist鈥�, because it keeps people and cattle out of some
regions.