African animal trypanosomosis is a parasitic blood disease transmitted by several species of the blood-sucking tsetse fly (Glossina spp.). The disease constrains livestock productivity and agricultural development across a wide swathe of Africa1. Fifty million cattle are found in tsetse-infested parts of the continent (Kristjanson et al. 1999). Annual losses from the disease are estimated to be at least US$ 1.6 billion (Swallow 1998) and could be as high as US$ 5 billion (Murray and Gray 1984). There are a number of ways to control the disease: tsetse flies can be suppressed using traps, targets or insecticides; preventive and curative drugs can be administered to threatened or sick animals; and breeds of livestock with genetic resistance to the disease can be selected and raised. The technical effectiveness of alternative control strategies—often involving more than one method—depends on interactions among such factors as tsetse and trypanosome species, topography, natural vegetation types, livestock breeds, livestock and human population distributions and densities, conditions in factor and product markets, and crop and livestock production systems (d'Ieteren et al. 1999).
1. The disease also has a human form and current estimates put the number of newly infected people at 300 thousand per year (Cattand 1999)
Trypanosomosis is particularly important in Ethiopia where about seven million cattle (15% of the continental total) are at risk of contracting the disease and where cattle are the main source of traction for crop cultivation. In 1991, the International Livestock Centre for Africa (ILCA) and the International Laboratories for Research on Animal Diseases (ILRAD)—-which together now comprise ILRI—-began conducting research on tsetse control in the south-western region of the country, in an area located in the upper reaches of the Ghibe Valley, 180 km south-west of the Ethiopian capital, Addis Ababa. The aim was to assess the efficacy and impacts of a then relatively novel tsetse control approach, namely applying insecticides as 'pour-ons' along the spines of cattle.2 The trial began in January 1991 and has been very successful in reducing tsetse challenge and disease prevalence, with considerable impacts on farm productivity and farmer incomes.
2. Tsetse and other biting flies landing on animals treated with pour-on insecticides are contaminated, fly away and die. If enough animals in a tsetse-infested area are treated, and if sufficient flies make contact with those animals, the pour-on technology can be extremely effective.
Prior to the intervention, the valley was heavily infested with three species of tsetse fly, namely Glossina morsitans submorsitans Newstead, G. pallidipes Austen, and G. fuscipes fuscipes Newstead. Following control, the apparent density of tsetse and biting flies in the region fell by 95%. This reduction in tsetse challenge led to a decrease in trypanosome prevalence in cattle of over 61%, despite a high level of resistance to all available trypanocidal drugs. The number of curative trypanocidal drug treatments per animal fell by 50%. Calf growth rate increased by 20% on average; calf mortality and abortion decreased by 57%. Average cow body weight was boosted by 4%, the cow:calf ratio by 49%, and adult male body weight by 8%. Between 1995 and 1997, expenditures on trypanocidal drugs fell by US$ 39 thousand, which more than offset the US$ 16 thousand cost of the pour-on. The additional benefits of increased output of meat (40%) and milk (30%) equalled US$ 146 thousand. This implied a benefit/cost ratio of 11.6 over two years and 9.3 projected over 10 years, and increases in annual household income of between 10 and 34% (Leak et al. 1995; Swallow et al. 1995; Woudyalew et al. 1999; Rowlands et al. (forthcoming)).
Most households in the area practice integrated crop–livestock farming, with animal draft power being the central integrating factor. The total number of cattle in the control area rose from 500 in 1991 to at least 6500 in 1997, contributing significantly to agricultural productivity via availability of draft animals (Woudyalew et al. 1999). Larger livestock holdings have implied more draft animals on average. This has resulted in significant increases in cropped areas, with each additional ox owned translating into between 0.6 and 0.9 ha more of cultivated land (Swallow et al. 1998).
Not only did ILRI scientists design the trial, ILRI undertook to procure pour-ons on the international market, store them, transport them to the nine supply points ('crushes'), and apply treatments to animals presented by farmers. ILRI team members periodically engaged local cattle owners in formal and informal discussions about the effectiveness of the pour-ons and the need for a minimum level of pour-on application to maintain low levels of tsetse density and trypanosomosis prevalence in the region. Local community organisations and participating cattle owners were responsible for building and maintaining the treatment centres in their localities. In the context of the current analysis, the most crucial aspect of the trial was that, while ILRI initially provided pour-on treatments to farmers free of charge, full cost-recovery was implemented after two years (Swallow et al. 1995). Since 1992, therefore, farmers have been deciding on pour-on use-rates and intensities for themselves.
