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Annual Report: CIRAD 2006

At-risk landscapes and tsetse fly behaviour: the bases for vector control strategies

In sub-Saharan Africa, animal trypanosomoses transmitted by tsetse flies have considerable economic consequences for the animal production sector. To control these diseases, it is vital to understand the ecology of tsetse flies, and particularly the factors that affect their vectorial capacity. Studies are under way, primarily in Burkina Faso, to determine these factors.

Treating cattle using an acaricide-insecticide foot bath, in Burkina Faso © J. Bouyer/CIRAD

In Burkina Faso, trypanosomoses are primarily transmitted by two tsetse fly species that live along streams and rivers: Glossina palpalis gambiensis and G. tachinoides. Studies of at-risk landscapes, and also of how the flies feed, are making it easier to target vector control strategies more effectively, on both a landscape and an animal scale, and to transfer a control technique used against ticks to tsetse flies.

Identifying at-risk landscapes

An initial series of studies concerned the relations between riparian plant ecotypes and tsetse fly densities in Mouhoun, a region in the Mid-West of the country. The landscapes along the river were analysed by spatial remote sensing. As the riparian forests were too small to be analysed directly, it was the surrounding pixels that were examined on images from the Landsat 7 TM satellite (30 m by 30 m pixels). These analyses pinpointed certain properties of the riparian belt, such as the degree of disturbance or the ecotype, by identifying clusters of similar neighbourhoods and comparing them with field surveys. The risk of cyclical trypanosome transmission was then estimated by calculating the entomological inoculation rate, which was equal to the relative density of the vectors multiplied by the percentage of infectious tsetse flies. This analysis served to locate trypanosome risk zones by considering these principal components of vectorial capacity over the whole of the Mouhoun loop, ie a 702-kilometre hydrographic network. It enabled the definition of three atrisk landscapes.

Land saturation due to increasing animal densities and cash crop extension, combined with reduced rainfall, is resulting in the increasing fragmentation of ecosystems propitious to tsetse flies. Riparian belts have thus become corridors enabling the flies to move between the remaining propitious zones, which surround protected areas. Studies of spread (by marking, release and recapture), population genetics and geometric morphometrics serve to quantify those movements and provide a clearer understanding of target population structure, their degree of isolation and their size.

Such studies, prior to vector control operations, are intended for major control projects on a whole-population level (also called area-wide management), notably under the Pan-African Tsetse and Trypanosomiasis Eradication Campaign (PATTEC). They serve to confine operations, but also to set up barriers to isolate more vulnerable subunits that may be attacked in succession.

Trophic behaviour and vector control

A study of the vectors themselves, and particularly of how they feed, revealed two determining specificities for trypanosomosis epidemiology and control. Firstly, the existence of a learning period, which steers trophic preferences towards the first host encountered. This discovery casts doubt on current epidemiological models, which do not take account of this factor and consider the trophic preference of individuals—one of the components of vectorial capacity—to be constant. Secondly, it observed tropism, which prompts tsetse flies to attack the ends of the members on cattle. This result has an immediate practical application: adapting an acaricide-insecticide foot bath in order to develop an integrated control strategy against both the tick Amblyomma variegatum and tsetse flies, which are the main vectors in the subhumid zones of West Africa. The technique is currently being practised in periurban zones of Burkina Faso, and demonstration foot baths are to be installed in neighbouring countries (Mali, Benin, Ghana, Chad, Cameroon, Central African Republic). Besides animal trypanosomoses, tsetse fly behaviour also has an impact on the epidemiology of sleeping sickness, and vector control centring on epicutaneous treatment of pigs has been organized in Guinea.

Contacts

Jeremy Bouyer, e-mail ; Laure Guerrini ; François Roger ; Laurence Vial

UPR: Epidemiology and Ecology of Animal Diseases

Partenaires

  • Agriculture and Veterinary Information and Analysis (AVIA-GIS, Belgium),
  • Centre international de recherche-développement sur l’élevage en zone subhumide (CIRDES, Burkina Faso),
  • Direction nationale de l’élevage (Guinea),
  • Direction nationale de l’élevage (Senegal),
  • Institut de médecine tropicale (IMT, Belgium),
  • Institut de recherche pour le développement (IRD, France),
  • International Atomic Energy Agency (IAEA, Austria),
  • Pan-African Tsetse and Trypanosomiasis Eradication Campaign (PATTEC),
  • Food and Agriculture Organization of the United Nations (FAO, Italy),
  • Programme national de lutte contre la trypanosomiase humaine africaine (PNLTHA, Guinea),
  • West African Economic and Monetary Union (UEMOA),
  • University of Neuchâtel (Switzerland), University of Oxford (United Kingdom).

This work was funded by Fragfly (Wellcome Trust), Saphyto, Ceva-santé animale, Bayer, IAEA, WECARD and UEMOA.

For further information

  • Website: FRAGFLY project
  • Bouyer J., 2006. Ecologie des glossines du Mouhoun au Burkina Faso : intérêt pour l’épidémiologie et le contrôle des trypanosomoses africaines. Thèse, université de Montpellier II, 212 p.
  • Bouyer J., Guerrini L., Desquesnes M., de la Rocque S., Cuisance D., 2006. Mapping African animal trypanosomosis risk from the sky. Veterinary Research, 37 : 633-645.
  • Camara M., Caro-Riano H., Ravel S., Dujardin J.P., Hervouet J.P., De Meeus T., Kagbadouno M.S., Bouyer J., Solano P., 2006. Genetic and morphometric evidence for population isolation of Glossina palpalis gambiensis (Diptera: Glossinidae) on the Loos islands, Guinea. Journal of Medical Entomology, 43 : 853-860.
  • Stachurski F., Bouyer J., Bouyer F., 2006. La lutte contre les ectoparasites des bovins par pédiluve : une méthode innovante utilisée en zone périurbaine subhumide du Burkina Faso. Revue d'élevage et de médecine vétérinaire des pays tropicaux, 58 : 221-228.