Herd-level bovine tuberculosis risk factors: assessing the role of low-level badger population disturbance.

David M Wright,W Ian Montgomery,Neil Reid,Adrian R Allen,Robin A Skuce,Rowland R Kao

doi:10.1038/srep13062

Abstract

Bovine TB (bTB) is endemic in Irish cattle and has eluded eradication despite considerable expenditure, amid debate over the relative roles of badgers and cattle in disease transmission. Using a comprehensive dataset from Northern Ireland (>10,000 km2; 29,513 cattle herds), we investigated interactions between host populations in one of the first large-scale risk factor analyses for new herd breakdowns to combine data on both species. Cattle risk factors (movements, international imports, bTB history, neighbours with bTB) were more strongly associated with herd risk than area-level measures of badger social group density, habitat suitability or persecution (sett disturbance). Highest risks were in areas of high badger social group density and high rates of persecution, potentially representing both responsive persecution of badgers in high cattle risk areas and effects of persecution on cattle bTB risk through badger social group disruption. Average badger persecution was associated with reduced cattle bTB risk (compared with high persecution areas), so persecution may contribute towards sustaining bTB hotspots; findings with important implications for existing and planned disease control programmes.

Highlights

Bovine TB is endemic in Irish cattle and has eluded eradication despite considerable expenditure, amid debate over the relative roles of badgers and cattle in disease transmission
We address the following questions: i) What are the cattle-related risk factors for herd-level bTB detection? ii) Is cattle bTB risk associated with badger social group density and/or habitat suitability? iii) Is badger persecution associated with increased bTB risk?
Importing animals from the Republic of Ireland was associated with an additional increase in risk of 17% (Table 2)

Summary

Introduction

Bovine TB (bTB) is endemic in Irish cattle and has eluded eradication despite considerable expenditure, amid debate over the relative roles of badgers and cattle in disease transmission. Cattle risk factors (movements, international imports, bTB history, neighbours with bTB) were more strongly associated with herd risk than arealevel measures of badger social group density, habitat suitability or persecution (sett disturbance). Average badger persecution was associated with reduced cattle bTB risk (compared with high persecution areas), so persecution may contribute towards sustaining bTB hotspots; findings with important implications for existing and planned disease control programmes. A range of herd-level risk factors for bTB have been identified in previous studies, the composition of such lists varies depending on the context, scale of investigation and study period[2,3,4,5]. In parts of Great Britain where badger populations have increased rapidly (i.e. south-west England)[12,13], the estimated risk of bTB infection at the herd-level is positively associated with badger population density[10]. Besides officially sanctioned culls there is evidence of low but sustained levels of illegal culling and sett disturbance (badger persecution) across Great Britain[12,19,20]

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Conclusion