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Programme Against African Trypanosomosis (PAAT)

Stage 3: initiating AAT elimination

The focus of the PCP’s final stages (3 to 5) is to create sustainable AAT-free areas. In particular, the focus of Stage 3 is the interruption of AAT transmission. Many activities already described for Stage 2 have to be carried out (or continued) in Stage 3, but emphasis differs. The collection of baseline and monitoring data is more intensive than in Stage 2, so as to address the higher information requirements of an elimination campaign [1, 2]. Focus is on tsetse data, including longitudinal monitoring of tsetse densities [3], age structure and natural abortion rates (the latter only needed to measure SIT-induced abortion rates, if a SIT component is planned) [4]. At very low tsetse densities, advanced statistical analysis of tsetse catches is needed to measure the probability of having achieved tsetse elimination [3]. Despite the emphasis on tsetse data, essential AAT [5-7] and socio-economic data [8] are still needed.

In order to eliminate tsetse flies in the target area, a suppression phase focuses on the reduction of tsetse densities, while a second mop-up phase completes the elimination. A range of tools can be used in the process, either alone but preferably in combination following an integrated pest management approach. These include the methods already mentioned in Stage 2 such as ITC and ITT. However, more expensive methods can be used in an elimination context [9], like SAT [10] and SIT [11, 12]. Some of the methods are more appropriate for suppression, while others are more effective for elimination. For example, SIT is the only technique with inverse density dependent efficiency (i.e. it works best when wild tsetse densities are very low), so it is particularly efficient for elimination [13].

Once tsetse flies are eliminated, the need to clear the parasite reservoir in livestock should be evaluated. A blanket treatment may be particularly important to eliminate T. vivax, whose mechanical transmission can occur in the absence of tsetse. Control and surveillance of livestock movement may also be necessary to reduce the risk of disease reintroduction.

Compared with Stage 2, AAT elimination requires more centralized, top-down management and coordination. Despite this, farmers’ sensitization and involvement remains crucial. Public information campaigns (e.g. radio, TV, etc.) ensure the engagement and support of the beneficiaries, who can also contribute directly to the campaign (e.g. if ITC is used).

Transition from Stage 3 to Stage 4 is linked to the interruption of AAT transmission (i.e. not directly to the elimination of the tsetse vector).

References

  1. Bouyer, J. et al., Stratified entomological sampling in preparation for an area-wide integrated pest management program: the example of Glossina palpalis gambiensis (Diptera: Glossinidae) in the Niayes of Senegal. J. Med. Entomol., 47 (2010), pp. 543-552
  2. Percoma, L. et al., Enquêtes entomologiques préparatoires à une lutte à grande échelle contre les glossines, assistées par un système d’information géographique: cas de la Pattec au Burkina Faso. Rev. Elev. Med. Vet. Pays Trop., 68 (2016), pp. 157-165
  3. Dicko, A.H. et al., Using species distribution models to optimize vector control in the framework of the tsetse eradication campaign in Senegal.
  4. Vreysen, M.J et al., Tsetse flies: their biology and control using area-wide integrated pest management approaches. J. Invertebr. Pathol. 112 (2013), S15-S25
  5. Seck, M. et al., The prevalence of African animal trypanosomoses and tsetse presence in Western Senegal. Parasite, 17 (2010), pp. 257-265
  6. Adam., Y. et al., Bovine trypanosomosis in the Upper West Region of Ghana: entomological, parasitological, and serological cross-sectional surveys. Res. Vet. Sci., 92 (2012), pp. 462-468
  7. Sow, A. et al.. Baseline survey of animal trypanosomosis in the region of the Boucle du Mouhoun, Burkina Faso. Res. Vet. Sci., 94 (2013), pp. 573-578
  8. Bouyer, F. et al., Ex-ante benefit-cost analysis of the elimination of a Glossina palpalis gambiensis population in the Niayes of Senegal. PLoS Negl. Trop. Dis., 8 (2014), p. e3112
  9. Shaw., A. et al., Mapping the benefit–cost ratios of interventions against bovine trypanosomosis in Eastern Africa. Prev. Vet. Med., 122 (2015), pp. 406-416
  10. Kgori, P.M. et al., The use of aerial spraying to eliminate tsetse from the Okavango Delta of Botswana. Acta Trop., 99 (2006), pp. 184-199
  11. Vreysen, M.J. et al., Sterile insects to enhance agricultural development: the case of sustainable tsetse eradication on Unguja Island, Zanzibar, using an area-wide integrated pest management approach. PLoS Negl. Trop. Dis., 8 (2014), p. e2857.
  12. Vreysen, M.J. et al., Glossina austeni (Diptera: Glossinidae) eradicated on the island of Unguja, Zanzibar, using the sterile insect technique. J. Econ. Entomol., 93 (2000), pp. 123-135
  13. Bouyer, J. et al., Trypanosomosis: control methods. P.-C. Lefèvre (Ed.), Infectious and Parasitic Diseases of Livestock, Éditions Lavoisier (Tec & Doc) (2010), pp. 1936-1943