Bovine tuberculosis in Northern Ireland: Surveillance, Biosecurity and Farmers' Attitudes

Abstract

Bovine tuberculosis (bTB), caused by Mycobacterium bovis, has a global distribution and is one of the most important infectious diseases affecting the cattle industry in Northern Ireland. Although it primarily affects cattle, other mammals including humans can be infected as well. A compulsory eradication programme based on testing and removal of positive animals has been in place since 1959 in Northern Ireland. However, bTB still persists in the cattle population due to a variety of reasons including residual infection within the herd, recurrent infection of herds and persistence of infection in the locality. This thesis aimed to address some of these problems focussing on surveillance, biosecurity and farmers’ attitudes in relation to bTB control. The main issues considered included: the imperfect sensitivity of the currently available diagnostic tests the little sense of ownership by farmers in relation to bTB control the nature of the farming industry in Northern Ireland the presence of a wildlife reservoir (European badger, Meles meles) Surveillance for bTB in Northern Ireland is mainly based on a combination of the single intradermal comparative cervical tuberculin (SICCT) test and routine post-mortem examination. Estimation of diagnostic test characteristics showed that both tests were found to have a near perfect specificity but the reported sensitivity was not for either test resulting in the potential of leaving infected animals behind. Residual infection was found to be linked to the number of SICCT test reactors disclosed during the bTB breakdown with breakdowns with multiple reactors especially being a risk factor for future bTB breakdown regardless of the confirmation status of the breakdown. Focusing on post-mortem inspection, potential risk factors that affect the development of visible bTB lesions in SICCT test reactors were evaluated and disclosed creating more vigilance during the post mortem examination of animals in specific categories. In Northern Ireland and the rest of the British Isles, all aspects of the bTB eradication programme are currently controlled by Government resulting in a lack of direct involvement of the farming industry. This thesis sets a baseline level as to what farmers’ current attitudes are towards bTB control and bTB related biosecurity in Northern Ireland. There was a lack of adoption of bTB related biosecurity measures by farmers, especially in relation to badgers. Furthermore risk factors for bTB breakdown at the farm management level were disclosed including the presence of accessible badger setts, the observation of live badgers on the farm and feeding magnesium supplement and meal on top of the silage. The potential for nose-to-nose contact and therefore bTB transmission between cattle of neighbouring herds was also found to be cause for concern. In conclusion, bTB in cattle is a complex disease with many challenges still to be faced. However, this thesis has aimed to address some of these difficulties, which are hoped to contribute, along with further research, to further control and ultimately eradication of bTB in Northern Ireland.