Control of bovine tuberculosis and Johne's disease in cattle
Abstract
If the diagnosis of mycobacterial disease in cattle is challenging, the diagnosis of infection is even more so. This is because of the biology of the organisms involved, the pathogenesis of the diseases characterised by uncertain, frequently prolonged and non-linear progression and intermittent shedding of the infectious organism, and limitations, particularly with respect to sensitivity, of the commonly used testing technologies and strategies. Infected animals, however, need to be identified and managed if disease is to be controlled and perhaps even ultimately eradicated. Possible strategies to facilitate this are discussed.
The Welsh First Minister, Mark Drakeford, in response to questions raised in the Senedd, recently confirmed that 70% of new bovine tuberculosis (bTB) breakdowns in cattle herds in the low bTB-risk area in Wales (meaning a significant challenge from any reservoir of in-fection within a local wildlife population is un-likely) can be traced back to the introduction of one or more Mycobacterium bovis infected animals into the herd. A possible interpretation of Mr Drakeford's statement is that some farmers are knowingly trading M. bovis infected animals, but this seems hardly fair or charitable. What farmer would knowingly purchase an infected or diseased animal and then introduce it into his or her herd, potentially compromising the viability of the entire cattle enterprise on the farm? In addition, the trading of such animals would be illegal; it is only permitted to sell animals that originate from officially bTB-free (OTF) herds and, if necessary, which have passed a ‘skin’ test within the 60 days prior to the sale. All animals that fail a statutory bTB test, and the herds they are part of, are placed under movement restrictions and the individual animal(s) in question is/are subject to compulsory purchase and slaughter.
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