Bovine tuberculosis (bTB) remains an important public health concern worldwide as a result of deficiencies in preventing and/or controlling measures targeting the spread of its causative agent Mycobacterium bovis. While the risk posed by M. bovis to human health is low in most developed countries, the main causes of concern related to M. bovis in industrialized countries are epizootics in domesticated and wild mammal populations. Infection with M. bovis remains a significant livestock zoonosis in the European Union where some member states experience a reemergence of the disease despite significant historical efforts to implement eradication plans. In Great Britain, the disease was eliminated from most cattle herds by 1960, with the exception of infection hotspots in southwest England, after the implementation of a herd testing and slaughter policy. However, efforts to completely eradicate bTB in Great Britain have been hampered by the maintenance of M. bovis in wildlife host populations, acting as reservoirs of infection, in particular badgers (Meles meles). Since 1979, incidence in British cattle has increased and the infection has become more geographically widespread. Over 7 million cattle were tested for bovine bTB in 2009 and one in ten herds experienced bTB-related movement restrictions during the year as a result of at least one member of the herd failing the tuberculin skin test or showing lesions consistent with bTB during the slaughterhouse inspection – an event known as a “herd breakdown”.
Local Cattle and Badger Populations Affect the Risk of Confirmed Tuberculosis in British Cattle Herds. 2011 PLoS ONE 6(3): e18058. doi:10.1371/journal.pone.0018058
Background: The control of bovine tuberculosis (bTB) remains a priority on the public health agenda in Great Britain, after launching in 1998 the Randomised Badger Culling Trial (RBCT) to evaluate the effectiveness of badger (Meles meles) culling as a control strategy. Our study complements previous analyses of the RBCT data (focusing on treatment effects) by presenting analyses of herd-level risks factors associated with the probability of a confirmed bTB breakdown in herds within each treatment: repeated widespread proactive culling, localized reactive culling and no culling (survey-only).
Methodology/Principal Findings: New cases of bTB breakdowns were monitored inside the RBCT areas from the end of the first proactive badger cull to one year after the last proactive cull. The risk of a herd bTB breakdown was modeled using logistic regression and proportional hazard models adjusting for local farm-level risk factors. Inside survey-only and reactive areas, increased numbers of active badger setts and cattle herds within 1500 m of a farm were associated with an increased bTB risk. Inside proactive areas, the number of M. bovis positive badgers initially culled within 1500 m of a farm was the strongest predictor of the risk of a confirmed bTB breakdown.
Conclusions/Significance: The use of herd-based models provide insights into how local cattle and badger populations affect the bTB breakdown risks of individual cattle herds in the absence of and in the presence of badger culling. These measures of local bTB risks could be integrated into a risk-based herd testing programme to improve the targeting of interventions aimed at reducing the risks of bTB transmission.