Modelling bovine spongiform encephalopathy

Abstract

SUMMARYA deterministic model for the spread of an important animal disease, bovine spongiform encephalopathy (BSE), is described. It is a sparse three-pool model, the pools corresponding to susceptible, infected and sick animals. Simulations illustrate the biological meaning of the parameters, and pinpoint how parameters affect epidemic characteristics: infectivity impacts on the leading edge of the epidemic and its intensity. The times when infection is introduced and when control is exercised determine the length and possibly the intensity of the epidemic. Finally, the (single) incubation rate influences the trailing edge of the epidemic. It is applied to data describing the recent UK BSE outbreak, with reasonable success. Apart from a scaling factor, only these four quantities were adjusted to achieve this. The contributions from greater modelling complexity are discussed. It is concluded that the simple model is well suited for grasping the essentials, whereas further detail is needed for a more mechanistic representation, in particular concerning incubation delays in developing infectiousness and clinical sickness.