Ex-ante benefit-cost analysis of the elimination of a Glossina palpalis gambiensis population in the Niayes of Senegal

Abstract

Background: In 2005, the Government of Senegal embarked on a campaign to eliminate a Glossina palpalis gambiensis population from the Niayes area (∼ 1000 km(2)) under the umbrella of the Pan African Tsetse and Trypanosomosis Eradication Campaign (PATTEC). The project was considered an ecologically sound approach to intensify cattle production. The elimination strategy includes a suppression phase using insecticide impregnated targets and cattle, and an elimination phase using the sterile insect technique, necessary to eliminate tsetse in this area.

Methodology/principal findings: Three main cattle farming systems were identified: a traditional system using trypanotolerant cattle and two "improved" systems using more productive cattle breeds focusing on milk and meat production. In improved farming systems herd size was 45% lower and annual cattle sales were €250 (s.d. 513) per head as compared to €74 (s.d. 38) per head in traditional farming systems (p<10-3). Tsetse distribution significantly impacted the occurrence of these farming systems (p = 0.001), with 34% (s.d. 4%) and 6% (s.d. 4%) of improved systems in the tsetse-free and tsetse-infested areas, respectively. We calculated the potential increases of cattle sales as a result of tsetse elimination considering two scenarios, i.e. a conservative scenario with a 2% annual replacement rate from traditional to improved systems after elimination, and a more realistic scenario with an increased replacement rate of 10% five years after elimination. The final annual increase of cattle sales was estimated at ∼ €2800/km(2) for a total cost of the elimination campaign reaching ∼ €6400/km(2).

Conclusion/significance: Despite its high cost, the benefit-cost analysis indicated that the project was highly cost-effective, with Internal Rates of Return (IRR) of 9.8% and 19.1% and payback periods of 18 and 13 years for the two scenarios, respectively. In addition to an increase in farmers' income, the benefits of tsetse elimination include a reduction of grazing pressure on the ecosystems.

Figure 1. Location of the study area, between Dakar and Thiès, Senegal.

The grid corresponds to 5*5 km cells that were used to design the entomological sampling strategy during the feasibility study . Pixels that could harbor Glossina palpalis gambiensis as predicted by the Maxent model are coloured in red. White lozenges correspond to the livestock farms geo-referenced during the preliminary survey whereas circles correspond to the farms surveyed during the socio-economic survey (see text for details).

Figure 2. Time table of the tsetse elimination project in the Niayes.

This table was used as a basis for the cost calculations.

Figure 3. Frequencies of cattle breeds in relation to tsetse presence and farming system.

The frequency of trypanotolerant cattle can be associated with two dominant groups, one based mainly on trypanotolerant cattle, and the second based on improved breeds, present almost only in the tsetse free area. The latter can be subdivided into two sub-groups based on the frequency of Gobra zebu cattle, which is the main breed for meat production in the area: an improved livestock keeping system targeting milk production, and a second one targeting meat production.

Figure 4. Boxplots of cattle herd size and annual sales of improved and trypanotolerant cattle.

Annual sales correspond to the total sales divided by the number of cattle present in the farm.

Figure 5. Distribution of the costs by partner (left) and component (right).

Figure 6. Comparison of the total costs of the project and increase in global cattle sales.

The figures (Euros) concern the Niayes area over a period of 30 years after the beginning of the project. Cattle sales include meat and milk sales. S1 corresponds to the scenario with a constant 2% annual replacement rate from traditional trypanotolerant farming systems to improved farming systems, and S2 to the scenario with an accelerated replacement rate according to the sociology of innovation (see text for details).