Trends in Microbiology
OpinionPublic health and bovine tuberculosis: what's all the fuss about?
Section snippets
Control and re-emergence of tuberculosis in British cattle
Historically, tuberculosis caused by Mycobacterium bovis (bovine tuberculosis, bTB) was a major public health issue in the UK. bTB in humans was widespread in the UK before the introduction of pasteurisation of milk in the 1960s: in the 1930s, 40% of dairy cows were infected and 0.5% had tuberculous mastitis [1]. During this period, approximately 2500 people died annually from bTB. Therefore, measures were introduced to eliminate bTB from the UK. As a result, by the 1970s, bTB was eliminated
Transmission of bTB to humans rarely occurs in the UK
Before milk pasteurisation, M. bovis was isolated from 8% of churn samples and almost all 3000-gallon tankers [4] suggesting widespread exposure to bTB. Since milk pasteurisation was generally introduced in the UK in the early 1960s, bTB in humans has declined dramatically. Between 1993 and 2003, 315 human cases of bTB were confirmed [5]. Among the affected people, only 14 had been born in the UK after 1960, whereas most of them had been born either before 1960 (265 cases) or outside of the UK
bTB is a food borne disease in humans
Declining numbers of human cases despite massive increases in affected cattle is consistent with the hypothesis that bTB is a food borne disease transmitted by milk. Indeed, a recent familiar outbreak of bTB in Ireland was as a result of the consumption of unpasteurised milk [10]. Nevertheless, belief is widespread that transmission from cattle to humans by aerosol is also important. For example, Smith and Clifton-Hadley [11] concluded that bTB control in cattle must continue to prevent cattle
The economics of bTB
bTB control is big business. In 2007, there were 4172 new herd breakdowns in England and Wales [2]. The official figures probably underestimate the true numbers of cattle affected by bTB owing to, for example, the lack of sensitivity of surveillance at abattoirs [19]. Nevertheless, the direct costs can be estimated as £13,981 per breakdown [20]—overall in excess of £58 million. A detailed breakdown of expenditure [20] shows that expenditure is due to programme implementation. No animal health
Misallocation of resources
Currently the UK invests large amounts of public resource to prevent bTB, which is essentially an animal disease. In the absence of data demonstrating economic benefits to animal health, such investment is, in our opinion, a clear example of misallocation of resources. If there are economic benefits to agriculture, then the industry rather than the tax payer should bear most of the costs because of the principles of cost sharing such as those reviewed by More [25]. From a public health
A new way forward
The results of the randomised trial of badger culling (RTBC) in the UK suggested that badger culling is an ineffective use of public money. Indeed, the evidence suggested that culling not only wastes resources but it might worsen the problem [34] and is unlikely to be economically effective [20]. However, it is also possible that badger culling might have some positive effects, as there have been criticisms of the interpretations of the RTBC both in terms of statistics and study design (see
Concluding remarks
More and more extreme measures for the control of bTB are largely supported by the farming industry and the veterinary profession [42]. Ironically, in the first half of the last century, farmers, consumers and legislators repeatedly resisted attempts to make testing of cattle and, more importantly, pasteurisation of milk compulsory in Britain, despite overwhelming evidence (particularly from the USA [43]) of its positive impact on public health.
In light of the evidence we have presented here,
Glossary
- Cost–benefit analysis
- the financial return of a control programme. A programme where the financial benefit of intervention is less than the costs of such an intervention has a negative cost benefit.
- Cost-effectiveness
- the cost of an intervention programme in terms of the improvement in public health. Highly cost-effective programmes will result in gains of many QALYs, or reduction in many DALYs lost, at modest cost.
- DALY
- Disability Adjusted Life Year. This is the measure of human population health
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