Effect of culling and vaccination on bovine tuberculosis infection in European badger (Meles meles) population by spatial simulation modelling
Ab s t r a c t
The control of bovine tuberculosis (bTB) in cattle herds in the Republic of Ireland (ROI) is partially hin-dered by spill-back infection from wild badgers (Meles meles). The aim of this study was to determine therelative effects of interventions (combinations of culling and/or vaccination) on bTB dynamics in an Irishbadger population. A spatial agent-based stochastic simulation model was developed to evaluate theeffect of various control strategies for bovine tuberculosis in badgers: single control strategies (culling,selective culling, vaccination, and vaccine baits), and combined strategies (Test vaccinate/cull (TVC)), splitarea approaches using culling and vaccination, or selective culling and vaccination, and mixed scenarioswhere culling was conducted for five years and followed by vaccination or by a TVC strategy. The effectof each control strategy was evaluated over a 20-year period. Badger control was simulated in 25%, 50%,and 75% area (limited area strategy) or in the entire area (100%, wide area strategy). For endemic bTB,a culling strategy was successful in eradicating bTB from the population only if applied as an area-widestrategy. However, this was achieved only by risking the extinction of the badger population. Selectiveculling strategies (selective culling or TVC) mitigated this negative impact on the badger population’s via-bility. Furthermore, both strategies (selective culling and TVC) allowed the badger population to recovergradually, in compensation for the population reduction following the initial use of removal strategies.The model predicted that vaccination can be effective in reducing bTB prevalence in badgers, when usedin combination with culling strategies (i.e. TVC or other strategies). If fecundity was reduced below itsnatural levels (e.g. by using wildlife contraceptives), the effectiveness of vaccination strategies improved.Split-area simulations highlighted that interventions can have indirect effects (e.g. on population size) innon-treatment areas. Our model suggests that mixed control strategies could maintain infection preva-lence to a low level for a considerable period even with a growing population. The model supported thehypothesis that culling strategies appeared to be the most effective method for the control of bTB in bad-gers using parameters, where available, from ROI, either singly or in combination with other strategies. Inthis model, the success of a vaccination strategy depended partially upon population density and the pro-portion of the population infected, therefore an initial culling program (to reduce density and/or removeinfected badgers) followed by long-term vaccination may be effective in controlling bTB in badgers.