Models for regional heartwater epidemiology in a variable environment

LEVINS, R. 2000. Models for regional heartwater epidemiology in a variable environment. Onderste­ poort Journal of Veterinary Research, 67:163-165 A model of the epidemic dynamics of heartwater within a cattle production unit was presented by Yonow et al. (1998). Here, the model is expanded to a reg ion consisting of several farms to study the effect of environmental variability on control strategies. We have shown that: • In a region , where the environment of each farm is modelled with constant epidemiologic param­ eter values, while the between-farm parameter values differ, regional variation in the removal rate of infected cattle increases the average fraction of infected cattle across the region , while regional variation 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 epidemiologic parameters of each farm are time-variant, then temporal variation in both the transmission rate and removal rate increases the average fraction of infected cattle across the region , thereby requiring control measures that keep both parameters uniform.