Eco-social analysis of an East African agro-pastoral system: management of tsetse and bovine trypanosomiasis.

A key constraint for development of many East African agro-pastoral communities is African animal trypanosomiasis or nagana caused by Trypanosoma spp. and vectored by species of tsetse flies (Glossina spp.). Suppression of trypanosomiasis through trapping of tsetse fly populations was conducted from 1995 to 2005 at and near Luke, Southwest Ethiopia. Odor baited mass trapping technology was used to suppress adult fly populations to very low levels while tryponocidal drugs were used to treat trypanosome infections in cattle. Data on ecological, economic and social variables were collected and analyzed in the context of eco-social dynamics in the community. The bio-economicmodel of Regev et al. [Regev,U., Gutierrez, A.P., Schreiber, S.J., Zilberman, D., 1998. Biological and Economic Foundations of Renewable Resource Exploitation. Ecological Economics 26, 227-242] and Gutierrez and Regev [Gutierrez, A.P., Regev, U., 2005. The bioeconomics of tritrophic systems: applications to invasive species. Ecological Economics 52, 382-396]was used as amethodological framework for qualitative evaluation of the effects of tsetse/trypanosomiasis suppression on ecological, economic and social aspects. An objective function for single farmers was formulated to determine the optimal harvesting level of cattle, exposed to high and low levels of risk from tsetse/trypanosomiasis, as measured by the discount rate (δ) for a given base level pastoral resource (R=pasture or forage for cattle). The socially optimal objective function for resource exploitation by all farmers is that which maximizes the present value of utility of individuals expending revenues (consumption) from the revenue stream in ways that enhance the quality of life and yet assures the persistence of the resource base over an infinite time horizon (i.e., renewable resource sustainability). The bio-economic model predicts that reducing risk (δ) from tsetse and disease increased the cattle populations and their marginal value. The model also predicts that the interaction of decreased δ and increased productivity (θ) can lead to increased human and cattle populations and hence to over-exploitation of base resources (pastures) that lower environmental carrying capacity and reduced sustainability. Trap catches indicated that tsetse populations were reduced to very low levels, while the disease prevalence decreased from 29% to 10%. This led to a substantial increase in cattle including oxen populations, increased calving rates, increased milk production and increased the per-capita income. The availability of oxen allowed an increase in cultivated land from 12 ha in 1995 to 506 ha in 2005. Revenues (consumption) were invested in the purchase of more cattle and the establishment of a school for educating village children. Increases in land allocated to crops and other sources of income were also found. The bioeconomic model predicts the solution of the trypanosomiasis problems so transforms the East African agro-pastoral communities that new social structures will be required to cope with the ecological, economic and social consequences of this technological changes on sustainable development (sensu [Goodland, R., 1995. The concept of environmental sustainability. Annual Review of Ecology and Systematics 26, 1- 24]). This insight should not be lost in international rural development programs.