A model of bovine tuberculosis in the badger Meles meles:: an evaluation of different vaccination strategies

1. In recent years bovine tuberculosis (TB) incidence in cattle has been increasing in south-west England. The European badger Meles meles is implicated in the transmission of TB to cattle and has been the subject of culling operations in an attempt to control the disease. 2. An individual-based, spatial, stochastic, simulation model was used to investigate the control of TB in the badger by various badger-vaccination strategies. Nearly all population and epidemiological parameters were derived from a single long-term study site. Heterogeneous carrying capacities (the maximum number of breeding females per badger social group) and different sized badger territories were used to simulate natural heterogeneity. The model included the transmission of TB from badgers to cattle to allow reactive vaccination of badgers, i.e. in response to positive cattle TB test results. 3. The model predicted that badger populations with reduced contiguity (e.g. natural barriers) between social group territories would have a lower TB prevalence. 4. In the absence of information on the true prevalence of TB in badger social groups, vaccinating 80% of groups at a low vaccine probability (10% successfully immunized) was more effective in the model at reducing prevalence of TB in badgers, than vaccinating 10% of the groups at a higher probability (80% successfully immunized). 5. Although a lower cost option, vaccinating badgers purely in reaction to cattle herd infections took longer to reduce badger TB prevalence to 50% than proactive strategies (7-20 years compared with 3-5 years). Simulations suggested that at least 40% of healthy badgers need to be immunized each year to eradicate TB in the badger. The model indicated that vaccination of badgers is a viable alternative to badger culling for the control of TB in cattle. Combined control policies were not investigated. 6. Synthesis and applications. Widespread proactive vaccination appears to be the most effective strategy for disease control. Initial proactive vaccination followed by localized reactive vaccination can lead to a greater reduction in disease prevalence for less effort. This is likely to be a global finding for the control of wildlife diseases, although the optimal duration for a proactive campaign will depend upon specific circumstances (e.g. detection rate of disease).