Is Mycobacterium bovis really a significant health risk for humans? Print this pagePrint this page

The existing policy exists because bovine TB is a zoonosis (a disease that can be transmitted to humans from animals). It is purely because of the public health consequences of M.bovis infection that the epidemiology of the disease has historically been of great interest but is this now so relevant for developed countries such as the UK. However, there is some evidence that M bovis does not establish itself in human beings as readily as M tuberculosis (the human form). (Ref. 1) The precise incidence of human disease caused by M bovis is unknown. Before the 1960's it was estimated at 5 and 20% of human tuberculosis cases in the developed countries. Nowadays though, despite claims by some that the disease is endemic in many areas of the UK, it is estimated at just 0.59% to 1% of human tuberculosis cases (Ref. 2). In countries where bTB is still common and milk pasteurisation rare, it is estimated that 10-15% of human cases of tuberculosis are caused by M bovis infection. Milk is still regarded as the principle vehicle for transmission to humans, so there is therefore negligible risk if milk is boiled or pasteurised. The Health Protection Agency confirms that current risk posed by M. bovis to human health in the UK is considered negligible Ref. 3).

In the paper (Ref. 4) by the Professors Paul and David Torgerson, 'Public health and bovine tuberculosis: what’s all the fuss about?' it states that: 'In the UK, cattle-to-human transmission is negligible. Aerosol transmission, the only probable route of human acquisition, occurs at inconsequential levels when milk is pasteurised, even when bTB is highly endemic in cattle.' It goes on to say that; 'Before milk pasteurisation, M. bovis was isolated from 8% of churn samples and almost all 3000-gallon tankers suggesting widespread exposure to bTB. Even then most did not get the diease. Since milk pasteurisation was generally introduced in the UK in the early 1960s, bTB has declined drastically.'

‘Public Health and bovine tuberculosis – what’s all the fuss about?’ is a very well researched and referenced article, which concludes that bTB control in cattle is irrelevant as a public health policy and there is little evidence either for a positive cost benefit in terms of animal health of bTB control. It suggests that such evidence is required; otherwise there is little justification for the large sums of money spent on bTB control in the UK. It states that in reality cattle-to-human transmission is negligible. Aerosol transmission, the only probable route of human acquisition, occurs at inconsequential levels when milk is pasteurised, even when bTB is highly endemic in cattle. It goes on to say that there is little evidence for a positive cost benefit in terms animal health of bTB control. Is it now time for a radical re-think on policy?

Professor Paul R Torgerson currently holds the Chair of Veterinary Epidemiology at the University of Zurich, Switzerland. Previously he was a Professor at Ross University, a research associate professor at Zurich University, a lecturer at University College Dublin and a research fellow at Cambridge University. He holds a degree in veterinary medicine and a PhD, both awarded by the University of Cambridge. He is also a diplomat of the European College of Veterinary Public Health and a member of the World Health Organisation’s Foodborne Disease Burden Epidemiology Reference Group. Professor David Torgerson is currently Professor and Director of the York Trials Unit, Department of Health Sciences, University of York. He has an MSc in Health Services Research (Hull), a Diploma in Health Economics (Tromso) and a PhD in Public Health Medicine (Aberdeen).

Ref. 1 JM Grange, 1995 'Human Aspects of Mycobacterium Bovis Infection'

Ref 2. RM Hardie and JM Watson, 1992, 'Mycobacterium bovis in England and Wales, past, present and future'.

Ref. 3 www.hpa.org.uk/webw/HPAweb&Page&HPAwebAutoListName/Page/1204619502284?p=1204619502284
Health Protection Agency, section on Mycobacterium bovis.

Ref. 4 ‘Public Health and bovine tuberculosis – what’s all the fuss about?’, by Paul R Torgerson and David J Torgenson can be read at http://www.zora.uzh.ch/47412/



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