Fox Contact Behaviour and Rabies Spread: A Model for the Estimation of Contact Probabilities Between Urban Foxes at Different Population Densities and Its Implications for Rabies Control in Britain

Abstract

1. Contacts between susceptible and infectious individuals determine how fast a disease will spread. However, they are difficult to measure in the wild, and most models of disease spread have been forced to use estimated or derived values. 2. In this paper, a mathematical relationship between fox home range size and population density is derived from the literature and combined with behavioural data on movement patterns and encounters from urban Bristol, UK to formulate a predictive model of inter-group contact probabilities over a range of population densities. 3. This contact probability-population density relationship is used to formulate a revised version of the rabies model of Smith & Harris (1991), which is the model used by the Ministry of Agriculture, Fisheries and Food as the basis of its rabies control policy for an outbreak of the disease in an urban area of Britain. 4. The original and revised versions of the model are compared in terms of their predictions for the rate of rabies spread and their implications for rabies control in specific urban areas. 5. An equivalent probability of successful rabies control is achieved by 5-15% lower fox control for the revised model compared with the original one. The greatest differences between the probability of successful rabies control for a given level of fox control under the two versions of the model occur in winter. 6. The revised model predicts that the rate of rabies spread will be slower than predicted by the original model. This is due to the lower inter-group contact probabilities used in the revised model. Thus, there will be a greater chance of containment and elimination of the disease within a specified control area than was suggested by the original model. 7. The heterogeneous nature of the urban landscape probably results in a lower frequency of contacts than would be observed between foxes living at the same densities in rural environments.