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Tsetse and trypanosomiasis
If we have been controlling tsetse for so long, why are they still a problem?
This question has been the subject of several books and remains a controversial subject. However, the answer can be summarised as follows.
There have been a few large-scale successes, with countries such as Botswana, South Africa and Zimbabwe eliminating tsetse from most of their farming areas. However, these countries are at the natural limits of tsetse distribution, and the national successes are relatively slight when assessed on a continental scale.
Trypanosomiasis in Zimbabwe for example, has been largely eliminated three times in the past hundred years. About half the country (~200,000 square kilometres) was probably infested by tsetse in the 1850s. A pandemic of rinderpest at the end of the 19th century killed huge numbers of wild hosts, and, as a result, tsetse disappeared from most of the country.
Over the next 50 years, the host and fly populations recovered and trypanosomiasis returned as a major problem. Between 1950 and 1975, large-scale control operations, based on the use of ground spraying with DDT and dieldrin and the destruction of wild hosts, eliminated tsetse from most of the country for a second time.
However, the war for independence in the 1970s made it difficult to protect these gains, and yet again tsetse returned to their pre-rinderpest limits. So, for the third time, Zimbabwe pushed the tsetse belt back to the edges of the country where it currently remains. The same sort of story can be applied to most tsetse-affected countries.
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