Bovine tuberculosis (TB) is one of the most complex, persistent and controversial problems facing the British cattle industry, costing the country an estimated £100 million per year1. The low sensitivity of the standard diagnostic test leads to considerable ambiguity in determining the main transmission routes of infection, which exacerbates the continuing scientific debate2,3,4,5,6. In turn this uncertainty fuels the fierce public and political disputes on the necessity of controlling badgers to limit the spread of infection. Here we present a dynamic stochastic spatial model for bovine TB in Great Britain that combines within-farm and between-farm transmission. At the farm scale the model incorporates stochastic transmission of infection, maintenance of infection in the environment and a testing protocol that mimics historical government policy. Between-farm transmission has a short-range environmental component and is explicitly driven by movements of individual cattle between farms, as recorded in the Cattle Tracing System2. The resultant model replicates the observed annual increase of infection over time as well as the spread of infection into new areas. Given that our model is mechanistic, it can ascribe transmission pathways to each new case; the majority of newly detected cases involve several transmission routes with moving infected cattle, reinfection from an environmental reservoir and poor sensitivity of the diagnostic test all having substantive roles. This underpins our findings on the implications of control measures. Very few of the control options tested have the potential to reverse the observed annual increase, with only intensive strategies such as whole-herd culling or additional national testing proving highly effective, whereas controls focused on a single transmission route are unlikely to be highly effective.
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This work was funded by BBSRC, the Wellcome Trust and EPSRC. We would like to thank G. Medley, L. Green, O. Courtenay, A. Ramirez-Villaescusa, J. Wood and L. Danon for helpful discussions on bovine TB dynamics. Thanks to A. Conlan and T. J. McKinley for advice on implementing SMC-ABC and to A. Conlan to setting up the Marx Bros cluster. The breakdown and reactor data was supplied by the AHVLA team (particularly A. Mitchell and R. Blackwell), the RADAR team and DEFRA.
This file contains Supplementary Text and Data 1-8 and additional references.
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What a Difference a Stochastic Process Makes: Epidemiological-Based Real Options Models of Optimal Treatment of Disease
Environmental and Resource Economics (2018)