Abstract
BackgroundIn the British Isles, control of cattle tuberculosis (TB) is hindered by persistent infection of wild badger (Meles meles) populations. A large-scale field trial—the Randomised Badger Culling Trial (RBCT)—previously showed that widespread badger culling produced modest reductions in cattle TB incidence during culling, which were offset by elevated TB risks for cattle on adjoining lands. Once culling was halted, beneficial effects inside culling areas increased, while detrimental effects on adjoining lands disappeared. However, a full assessment of the utility of badger culling requires information on the duration of culling effects.Methodology/Principal FindingsWe monitored cattle TB incidence in and around RBCT areas after culling ended. We found that benefits inside culled areas declined over time, and were no longer detectable by three years post-culling. On adjoining lands, a trend suggesting beneficial effects immediately after the end of culling was insignificant, and disappeared after 18 months post-culling. From completion of the first cull to the loss of detectable effects (an average five-year culling period plus 2.5 years post-culling), cattle TB incidence was 28.7% lower (95% confidence interval [CI] 20.7 to 35.8% lower) inside ten 100 km2 culled areas than inside ten matched no-culling areas, and comparable (11.7% higher, 95% CI: 13.0% lower to 43.4% higher, p = 0.39) on lands ≤2 km outside culled and no-culling areas. The financial costs of culling an idealized 150 km2 area would exceed the savings achieved through reduced cattle TB, by factors of 2 to 3.5.Conclusions/SignificanceOur findings show that the reductions in cattle TB incidence achieved by repeated badger culling were not sustained in the long term after culling ended and did not offset the financial costs of culling. These results, combined with evaluation of alternative culling methods, suggest that badger culling is unlikely to contribute effectively to the control of cattle TB in Britain.
Highlights
Public controversy surrounds efforts to control bovine tuberculosis (TB) in the British Isles
Dividing the post-trial period into six-month intervals revealed a significant (p = 0.038) linear trend over time, with the beneficial effect declining by 14.3% with each sixmonth interval (Figure 1)
The results presented here show the duration of reductions in cattle TB incidence associated with widespread badger culling
Summary
Public controversy surrounds efforts to control bovine tuberculosis (TB) in the British Isles. In the British Isles, control of cattle TB has been hampered by transmission of infection from wild badgers (Meles meles), and various forms of badger culling have been implemented to try to reduce such transmission [3]. Despite these efforts, the incidence of cattle TB remains high in both Britain and Ireland [4,5], with 2,738 confirmed herd breakdowns in Britain in 2008 [4] and national expenditure of over £100 million. A full assessment of the utility of badger culling requires information on the duration of culling effects
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