Models for regional heartwater epidemiology in a variable environment

A model of the epidemic dynamics of heartwater within a cattle production u nit was presented by Yonow et al. (1998). Here, the model is expanded to a region consisting of several farms to study the effect of environmental var iability on control strategies. We have shown that: In a region, where the environment of each farm is modelled with constant e pidemiologic parameter values, while the between-farm parameter values diff er, regional variation in the removal rate of infected cattle increases the average fraction of infected cattle across the region, while regional vari ation in the transmission rate of infection from ticks to cattle decreases the average fraction of infected cattle, thereby requiring control measures that keep the removal rate uniform and the transmission rate variable. In a region, where in addition to regional variation between farms, the epi demiologic parameters of each farm are time-variant, then temporal variatio n in both the transmission rate and removal rate increases the average frac tion of infected cattle across the region, thereby requiring control measur es that keep both parameters uniform.