Abstract
In this article, we review the epidemiology of East Coast fever (ECF), a tick-borne infection of cattle, in Kenya. The major factors associated with epidemiology of ECF include the agro-ecological zone (AEZ), livestock production system (LPS) and both animal breed and age. These factors appear to influence the epidemiology of ECF through structured gradients. We further show that the gradients are dynamically shaped by socio-demographic and environmental processes. For a vector-borne disease whose transmission depends on environmental characteristics that influence vector dynamics, a change in the environment implies a change in the epidemiology of the disease. The review recommends that future ECF epidemiological studies should account for these factors and the dynamic interactions between them. In Kenya, ECF control has previously relied predominantly on tick control using acaricides and chemotherapy while ECF immunization is steadily being disseminated. We highlight the contribution of ECF epidemiology and economics in the design of production system and/or geographical area-specific integrated control strategies based on both the dynamic epidemiological risk of the disease and economic impacts of control strategies. In all production systems (except marginal areas), economic analyses demonstrate that integrated control in which ECF immunization is always an important component, can play an important role in the overall control of the disease. Indeed, Kenya has recently approved ECF immunization in all production systems (except in marginal areas). If the infrastructure of the vaccine production and distribution can be heightened, large ECF endemic areas are expected to be endemically stable and the disease controlled. Finally, the review points the way for future research by identifying scenario analyses as a critical methodology on which to base future investigations on how both dynamic livestock management systems and patterns of land use influence the dynamics and complexity of ECF epidemiology and the implications for control.
Highlights
East Coast fever (ECF) is a tick-borne disease (TBD) of cattle whose aetiological agent is a protozoan parasite called Theileria parva
This review has found that all epidemiological states of ECF are evident in Kenya based on geographical region and/or livestock production systems
At any particular moment, the epidemiological states of ECF are a result of interaction of broad environment and animal genetic factors
Summary
East Coast fever (ECF) is a tick-borne disease (TBD) of cattle whose aetiological agent is a protozoan parasite called Theileria parva. These systems are characterized by variable population immunity to T. parva, probably due to the periodic and varying environmental and climatic suitability for the survival and development of the vector This situation exists in much of the highland areas of Kenya in which zebu cattle are maintained, as well as the Lake Victoria Basin (in parts of both Nyanza and Western provinces) and the Kenyan coastal strip (in Coast Province) (Figure 2) (all mainly in zones III and IV (Figure 1)). In certain regions, the pastoralists’ traditional grazing areas lay on very suitable habitats for the tick vector leading to the successful establishment of endemic stability An example of this scenario has been studied and documented in the Trans-Mara District in the south-western area of the Rift Valley Province (Figure 2): in one study, all calves (n = 116) became infected by 6 months of age with very low ECF-specific mortality (3% up to 6 months of age) [14]. Case-fatality Epidemiological factors (cattle ages sampled) incidence rate rates
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