Tsetse-transmitted trypanosomiasis is still an important constraint to agricultural development in the subhumid - including the wetter areas of the semi-arid zones - and humid zones of Africa. Tsetse flies infest an area of about 10 million km2 stretching across 40 countries in sub-Saharan Africa. The disease affects both humans and livestock. It is currently estimated that about 50 million people (Kuzoe, 1991) and 48 million cattle (Kristjanson et al., 1999) are at risk of contracting trypanosomiasis. On an individual basis, untreated animal or human trypanosomiasis will lead, at best, to a chronic debilitating condition and, at worst, to death.
Generally, the benefits of T&T control will derive from a reduced risk of contracting the disease - both human and animal - and a diminution in the incidence of trypanosomiasis, thereby reducing mortality rates and expenses incurred in prevention and disease treatment, and thus improving human health and the productivity of existing livestock. For decades, standard methodologies for benefit-cost analysis have been applied to assess the most cost-effective techniques of T&T control, and to evaluate the benefits and costs of control including those arising outside the direct boundaries of livestock development projects. In recent years, efforts have been directed at understanding and estimating the impacts of African animal trypanosomiasis control on land use and the environment (Reid, 1999; Bourn et al., 2001), and the impacts of African animal trypanosomiasis on livestock productivity, livestock management, crop production and human settlement (Govereh, 1999; PAAT, 2000). An overview of the control techniques is provided here to set the stage for a discussion of their suitability for control, large-scale use and amenability to community participation.
Historically, aerial and ground spraying have been the means used by public agencies to control trypanosomiasis. These techniques formed the backbone of large-scale tsetse control efforts until the 1980s (Swallow, 1994; Barrett, 1997). In recent years, however, concerns about the costs, sustainability and environmental safety of spraying, coupled with financial restrictions, caused a decline in the capacity to organize large-scale operations and the levels of supervision of several national control programmes.
The sterile insect technique (SIT) is based on the release of male tsetse flies that have been bred and sterilized in the laboratory, which then compete in the control area with the wild fertile males for the females to be fertilized. The technical feasibility of the SIT for tsetse control has been proven in a number of pilot programmes in East and West Africa (Cuisance et al., 1984; Brandl, 1985, 1988; Barrett, 1997). The high cost of the technique and complex logistics have favoured its initial use in a strategy to eradicate tsetse flies from isolated pockets before tackling continuous belts of infested land. The SIT works better as a mop-up operation. The release of sterile males would normally be preceded by a phase of tsetse suppression by the communities using traps, targets, pour-ons and chemotherapy. Community participation is thus a critical contributing factor to the success of this technique.
The decline in the use of spraying techniques helped to stimulate interest in traps and targets/screens that are often enhanced with attractant odours. Impregnated traps and targets attract and kill tsetse-fly species in a variety of situations. The technology is relatively simple and less environmentally polluting than spraying. Traps and targets are also inexpensive and lend themselves to possible community participation. Field problems exist, however, with losses because of theft, damage from humans, fire or loss from being washed away in the rainy season. Wildlife can also contribute to the loss of traps and targets.
Insecticide-treated livestock can be regarded as a modification of the trap and target technique whereby, instead of stationary targets, insecticide-treated domestic animals (treated by dip or pour-on), can be used as moving targets (Leak et al., 1995, 1996). Targets and pour-ons can be used in combination as non-polluting and cost-effective methods of combating trypanosomiasis, particularly in cattle. Pour-ons are most effective when cattle are present in sufficient numbers and represent the overwhelming proportion of the host complex of tsetse in the area, and when they are presented for treatment on a regular basis. Communities of a few villages increasingly and successfully use dips and hand spraying of pyrethroids to combat both tsetse and ticks.
The husbandry of trypanotolerant livestock remains a control technique that has been used by African farmers for centuries (FAO, 1987; dIeteren et al., 1998). Several West African breeds - short- and longhorns - including NDama and Baoulé, and a few East African breeds have been shown to have a superior ability to control trypanosomiasis. Indeed, these animals can survive and produce in areas of low to moderate tsetse challenge without the aid of drugs. Trypanotolerant cattle are raised under different management systems, sometimes along with trypanosusceptible breeds. These animals, however, may succumb to trypanosomiasis under high challenge or physiological stress. A trend among livestock farmers in West Africa towards large Zebu-type cattle is perceptible and raises concerns about the risk of extinction of small-sized trypanotolerant breeds (Tano et al., 2001).
Drug therapy has been the primary control technique for nearly 40 years in many African countries because of the lack of government funding and vector control infrastructures. It is estimated that about 35 million doses of trypanocides (isometamidium, diminazene and homidium) per year are currently used in Africa (PAAT, 1998a). Although the method has been effective, resistance of certain strains of trypanosomes to commonly used trypanocides has emerged (Codjia et al., 1993; PAAT, 1998a). New molecules are not yet available and the situation is unlikely to change in the foreseeable future. Drug prophylaxis should be considered where a proper drug management system could be established and maintained, for example on large farms and commercial ranches with profitable schemes.
The development of bait technologies has triggered two important shifts in the research and control of trypanosomiasis beyond the issue of costs and returns. The first is the involvement of beneficiaries as partners in order to contribute to the cost of the research and implementation of control activities while ensuring the long-term nature of the benefits derived from control (Okoth, Kirumire and Kapaata, 1991; Dransfield, Williams and Brightwell, 1991; Bauer et al., 1992; Kientz, 1993;). The second shift is the move away from large-scale, government-supported schemes to small-scale, community-based interventions where tsetse control can be regarded as a local public good. The new approach has implications for resource-use patterns and the social institutions - formal and informal conventions, norms and rules - that govern the use of resources and human welfare.
With the variety of technical options now available, there are good opportunities and possibilities for effective control of the disease (Budd, 1999). Each of the techniques has its advantages and disadvantages. For instance, the live bait technique requires a threshold density of cattle to control tsetse flies and ground spraying is reliant on good logistical support and access. However, there will always be a preferred technique, or combination of techniques, for each scenario depending on project size, fly species present, topography, cattle numbers, access, etc. National T&T control organizations in Africa need to make long-term decisions about which technique or combination of techniques they will use in the future. International donors on their part want to be sure that the appropriate control measures can be used. All in all, control programmes designed to reduce the number of tsetse flies and the incidence of trypanosomiasis need to incorporate socioeconomic factors and the cultural dimension as part of the design and evaluation plans while monitoring the implementation process to ensure sustainability.
The Programme against African Trypanosomiasis Programme Committee first commissioned this paper in October 1998 (PAAT, 1998b) with the purpose of amalgamating several draft papers on socio-economic and cultural impacts of T&T control in one, broad-ranging review paper. Thus, the scope of this review moved beyond single-case studies in East Africa to a wider geographical coverage of the continent (east, southern, west and central African regions). In addition to the three earlier commissioned PAAT draft position papers on the topic (Barrett and Okali, 1998a; Ssennyonga, 1998; Mwangi, Swallow and Roderick, 1998), this review has drawn on a variety of sources including published papers, results of recent field studies that had not previously been published, various workshop and conference reports and, to a much lesser extent, personal communications. Although much of the report concerns T&T control in livestock, efforts were made to review available references on socio-economic aspects of combating sleeping sickness and other human diseases. A corollary objective of the paper is to make available in one place a discussion of the major socio-economic and cultural aspects associated with the research, control and eradication of T&T in sub-Saharan Africa.
The paper is organized around three main topics:
1. an overview of socio-economic factors to account for in the research and control of T&T;
2. the role of sociocultural factors affecting community participation in the control activities to ensure sustainability of the benefits derived from T&T control; and
3. the importance of past lessons and experiences in strategic planning incorporating sociocultural aspects in design, monitoring and evaluation of T&T control programmes.