GIS (Geographical Information System) data can be easily used to help identify areas where disease control measures are best carried out. A current example is that of defining the best areas for feasibility studies for tsetse control in West Africa.
In this study, the
broad areas where impact is likely to be high were identified from the predicted
impact map as defined by PAAT-IS (the darker parts in the blue rectangle), and where control measures have not already been used (the grey parts).
As
a next step, farming intensity was estimated by overlaying data on cattle
densities and percentage of land under the cultivation cycle. This enables us to
highlight areas that may produce maximum economic benefit i.e. in
the tsetse belt but near centres of agriculture (shown in dark green and red)
from which farmers will
spread into any newly cleared areas.
Next the technical
feasibility of tsetse control has to be considered. Areas have to be identified
where both tsetse is (relatively) easy to clear, and there is minimal risk of
the new farming causing environmental degradation. In the picture on the left,
degradation is shown in vivid red, high population density in dark blue,
protected areas in dark green, and previously controlled areas in grey. Fly
presence is in yellow and bright green.
From this we can suggest that the suitable areas for control measures might be
anywhere that is yellow or bright green, but that the bright green (southern)
band is likely to be more difficult to clear.
However, we must also take the biology of the fly into account. Starting at its northern limit the
West-African fly belt can be divided in three bands. A northern band
where tsetse distribution is very patchy; a middle band where flies are more evenly spread over the
major river systems and finally a southern band where the flies also invade secondary and tertiary tributaries.
As you might expect, discrete fly populations, when identified, are more
easily dealt with than diffuse populations in the more humid southern parts of
the belt.
Unfortunately, however, the tsetse fly is a very strong flier, and can move
long distances. Therefore cleared areas can easily be reinvaded from
neighbouring (uncleared) areas. Arguably, therefore, clearing tsetse from the
drier parts might be achieved with minimal risk of reinvasion . Elsewhere, it
might prove necessary to maintain a barrier around a controlled area, where
flies are continuously being controlled.
Finally based on
the information given above, groups of river basins of different sizes (6,000 kmē,
60,000 kmē, 600,000 kmē) where selected to study the economic feasibility of
tsetse eradication. Three sizes of areas were identified: core areas, along the
edge of the tsetse belt (in
