Impacts of widespread badger culling on cattle tuberculosis: concluding analyses from a large-scale field trial

Background: Bovine tuberculosis (TB) has re-emerged as a major problem for British cattle farmers. Failure to control the infection has been linked to transmission from European badgers; badger cutting has therefore formed a component of British TB control policy since 1973. Objectives and design: To investigate the impact of repeated widespread badger cutting on cattle TB, the Randomised Badger Cutting Trial compared TB incidence in cattle herds in and around ten cutting areas (each 100 km(2)) with those in and around ten matched unculled areas. Results: Overall, cattle TB incidence was 23.2% tower (95% confidence interval (Cl) 12.4-32.7% tower) inside culled areas, but 24.5% (95% Cl 0.6% lower-56.0% higher) higher on land <= 2 km outside, relative to matched unculled areas. Inside the cutting area boundary the beneficial effect of cutting tended to increase with distance from the boundary (p = 0.085) and to increase on successive annual cults (p = 0.064). In adjoining areas, the detrimental effect tended to diminish on successive annual cults (p = 0.17). On the basis of such linear trends, the estimated net effect per annum for cutting areas similar to those in the trial was detrimental between the first and second cults, but beneficial after the fourth and later cults, for the range of analyses performed. Conclusions: Careful consideration is needed to determine in what settings systematic repeated cutting might be reliably predicted to be beneficial, and in these cases whether the benefits of such cutting warrant the costs involved. (C) 2007 International Society for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.