How important is “neighbourhood” in the persistence of bovine tuberculosis in Irish cattle herds?

Localised persistence of infection is a key feature of bovine tuberculosis (bTB) among cattle herds in the Republic of Ireland (ROI). A case-control study was conducted on the association between the occurrence of a bTB episode in 2006 in ROI herds, and the occurrence of bTB in previous years among neighbouring herd(s) within 1km, while controlling for own-herd bTB history and other risk factors. Neighbouring herds were grouped into three zones, and bTB incidence measures summarised within each zone and by calendar year (2001-2005). The results highlight an association between bTB and an increased animal incidence within two subsets of neighbouring herds: (i) herds directly contiguous during the previous 2 years, and (ii) herds at a distance of > 25 metres in the previous year. Further studies will be necessary to determine to what extent the association at (i) may be confounded by the existence of a wildlife (badger) source