Methods for Assessing the Impact of Infectious Diseases of Livestock — Their Role in Improving the Control of Newcastle Disease in Southern Africa

A framework for the impact assessment of disease control strategies for Newcastle disease (ND) is discussed. This includes linking epidemiological and economic data to predict the relative impact of different control interventions at different levels from farm to region. Epidemiological transmission models assume that village poultry are the reservoir of ND virus for other sectors. Simple models for transmission of the virus among village chickens predict that for vaccination to be effective, it must be conducted relatively frequently with a large proportion of chickens covered. Extrapolations to transmission between village and commercial sectors are suggested. Economic issues at farm level are considered most influential. Decisions to invest in national and regional projects will depend on the assessment of social equity impacts and cost-benefit and institutional analyses to assess relative benefits of private versus public sector interventions. Capturing the perspectives of all stakeholders in the ND control intervention process is considered crucial to both enhanced impact and sustainability of any control program. THE contributions of poultry to the economy of African countries and the livelihoods of its people are profound. FAO (FAOSTAT 2000) estimates that there are approximately 1.1 billion chickens in Africa. Sonaiya et al. (1999) have estimated that for most countries, in excess of 70% of total poultry production is from the village (family) sector and this sector provides a frequently unaccounted for economic asset of approximately US$ 5.75 billion. Crucially, in development terms, the village poultry sector preferentially benefits the rural poor and women (Sonaiya et al. 1999). Village chickens play several important social roles and a variety of poultry husbandry and ethnoveterinary practices have developed in many areas of Africa (Gueye 1999; Ibrahim and Abdu 1996). Many contributions to these Proceedings will highlight the crucial role of poultry to rural livelihoods in southern Africa. While the village poultry sector in Africa has evolved to be robust and sustainable, infectious diseases, particularly Newcastle disease (ND), are an important and sometimes catastrophic constraint (Alders and Spradbrow 1999, for several individual references). Vaccination against ND is a technically feasible (Biswas et al. 1996; Fontanilla et al. 1994; Samuel and Spradbrow 1991; Tantaswasdi et al. 1992; Wambura et al. 2000) but an economically non-sustainable control strategy for village chickens in Africa (Sonaiya et al. 1999). A variety of options to reduce control costs are being explored, including production of vaccine by developing country institutes (Spradbrow and Copland 1996; Wambura et al. 2000). The difficulties encountered in the control of ND in Africa and elsewhere in the developing world highlight the importance of considering both veterinary and socio-economic aspects in designing ND control programs. At the International Livestock Research Institute, we have used ex-ante impact assessment methods, combining both epidemiological and economic tools, in supporting decisions for the control of other infectious diseases of livestock (Mukhebi et al. 1999; Perry et al. 1999). In this paper, we propose a preliminary conceptual framework for considering technical and socioeconomic factors at different levels influencing the 1 International Livestock Research Institute, PO Box 30709, Nairobi, Kenya