Evidence gathered in the case studies confirms the band-like gradient suggested in Figure 2; the actual location of the different case studies is given in Figure 14 as compared with West African ecozones.
In most of Togo (Figure 14) drainage systems form an intricate web of favourable riparian tsetse habitats; savannah and forest species only persist in a few well-defined protected areas. The riparian tsetse habitats can hardly be avoided by livestock and appear not to be affected by crop encroachment at current cropping intensity levels. Farmers have responded to this by adopting trypanotolerant breeds. Nevertheless, low cattle numbers and the strong correlation observed between packed (red) cell volume (PCV), i.e. an indicator of the animal health status, and the integration of cattle and agriculture clearly show that these breeds, with little veterinary follow-up in traditional livestock production systems, do survive, although some production losses occur. In market-oriented livestock production systems, i.e. with access to cash and thus to veterinary inputs, livestock owners tend to increase the size of their cattle through cross-breeding trypanotolerant Somba females with trypanosusceptible Zebu bulls. This phenomenon was also observed on a larger scale elsewhere where it resulted in stabilized new cattle genotypes, for example, Borgou in Benin and Ketekou in Nigeria. In the northern part of Togo (Figure 14) climatic conditions are drier and suitable riparian habitats are more readily identifiable within a tropical dry forest landscape, allowing proper herd management practices that avoid contact with the vector. This area coincides with the southern distribution limit of trypanosusceptible Zebu breeds. Crop encroachment had a marked impact on G. tachinoides. As a result of proper management, tsetse control was successful and animal health significantly improved at the village level (Batawui et al., 2003).
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FIGURE 14 Background: West African ecozones derived from remotely sensed data on vegetation and temperature and ground-measured climatic data (source: PAAT-IS).
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The Sideradougou pastoral area in Burkina Faso (Figure 14) is more humid than northern Togo. Nevertheless suitable riparian habitats remain relatively easy to identify. Depending on livestock production systems, contact between vector and host may or may not be avoided. This largely depends on the availability of water resources. Different landscapes yield different risk levels identified as epidemiological hot spots. Control measures focusing on these hot spots not only decreased fly density but also disrupted trypanosomiasis transmission in such a way that a significant reduction in disease incidence could be measured. Sustainability largely depends on the organizational capacity of local communities. This includes the concerted choice of control methods (de la Rocque, in preparation).
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FIGURE 15 Scenarios for the dryer northern band and more humid southern band of West Africa are summarized.
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The Mouhoun river basin (Figure 14) includes a variety of riparian habitat types representative of the dry ecozone at a subregional level. The dominant cattle breeds are trypanosusceptible Zebu and, because it is a major cotton growing area, crop encroachment is relatively high. Based on field data on disease prevalence and anaemia, a distinct epidemiological pattern was shown; the trypanosomiasis problem was mainly confined along the main stream while low problem levels occurred along less important tributaries. Field data on tsetse allowed modelling of fly-ecology bands depicted in Figure 2.
TABLE 3
Vector suppression strategy on the Mouhoun river
basin
|
Mouhoun (see Figure 14) |
Fly ecology category |
Vector suppression strategy |
Needed complementary research |
|
1. Sources |
Ubiquitous |
Extensive web of drainage lines with suitable habitat. High epidemiological risk. Need for identification and control of epidemiological hot spots (Sideradougou model). |
Prior to considering elimination, link and relative isolation from southern river basins must be researched. A crucial factor is to avoid reinvasion downstream. |
|
2. Ascending leg |
Linear |
No agriculture in valley. Habitat preserved and identified. Important flood zones. Large-scale vector suppression possible. |
Monitoring fly population on the main stream and seasonal fluctuations along tributaries. |
|
3. Northern bend |
Linear- fragmented |
Within circumscribed habitat healthy tsetse populations. Outside harsh climatic conditions preventing reinvasion. |
Monitoring fly population. |
|
4. Descending leg |
Linear |
High anthropogenic pressure from east. Riparian habitat degraded. Stressed tsetse populations with high mortality rates. |
Research the possibility of using the high agriculture intensity stretch of the main stream as a barrier to upstream reinvasion. |
|
5. Major tributaries |
Linear |
Linear habitat in isolated pockets. Various levels of anthropogenic impact. |
Identification of fly pockets. Investigate genetic isolation of pockets and dispersion models. |
Fly-ecology category: as depicted in prediction output ( see Figure 13).
Any decision support towards tsete and trypanosomiasis management in West Africa must consider the fact that the epidemiology of tsetse-transmitted trypanosomiasis differs with varying climatic settings and land-use patterns. Therefore, the sustainable management of this major threat to animal health will have to be systematic, stepwise and pragmatic. A tentative list of the data inputs needed to achieve such a high level of integration is given in Figure 15.
Although data-driven decision support was successfully implemented in the southern humid band (e.g. Togo case study), this is not yet the case for the northern dry band. Many of the assumptions made during the desk study aiming at selecting priority areas for tsetse eradication have yet to be validated in the selected areas. Based on the experience gained on the Mouhoun river system in Burkina Faso, part of the Mali-Burkina Faso priority area for areawide vector eradication, an integrated approach including pathways for research is suggested in Table 3.
