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Mad Cow Disease in Hindsight—LESSONS LEARNT ABOUT DISEASE CONTROL PROGRAMS—A SHORT LITERATURE REVIEW

Dermot McNerney, NSW State Coordinator TSE, NSW DPI, Dareton

Posted Flock & Herd March 2015

BSE (Bovine Spongiform Encephalopathy, "Mad Cow Disease") was first reported in November 1986 in the UK2. It was thought at that time to be similar to Scrapie in sheep and goats. However Scrapie had been around for at least two centuries, had always been confined to sheep and goats, caused limited problems and the longstanding prevailing hypothesis was it was caused by 'a slow virus'.

Before BSE was first discovered, in 1982 Pruisner6 proposed the prion hypothesis for Scrapie and was met initially with scepticism and ridiculee.g.'proteins can't cause infectious disease'. However, within 12 months of the first case of BSE in 1986, Pruisner's hypothesis was considered proven. By 1988, 442 cases of BSE had been identified in the UK3. The same year, meat and bone meal (MBM) was identified as the source of this epidemic, which at that time was confined to the UK2. The UK introduced a partial ban on the feeding of MBM to ruminants. This measure curbed but did not eliminate the epidemic, as it was not tightened to become an absolute MBM ban which was fully enforced until 2001. Work by Wells et al.7 in 1998 concluded that most BSE infectivity was concentrated in the brain and spinal cord.

Further positive cases were identified in other countries from 1989 onwardse.g.Ireland '89, Portugal '90, France '913. Since 1986, nearly 191,000 positive BSE cases have been identified worldwide3. Approx 95% of these cases were in the UK, 3% in the rest of Europe and remainder in 6 other countries.

A likely link between BSE and vCJD (variant Creutzfeldt-Jacob Disease) in humans was first established in 1996 "followed by a media outbreak of apocalyptic scenarios sketching a man-made disaster of then unpredictable proportions"2. By 2000, the "Phillips Inquiry" report was published8, which was critical of intensive farming practices and the UK government responses which were identified as too secretive and unjustifiably reassuring in order to protect the agricultural industry8. About the same time, active BSE surveillance in EU states shattered the myth that many of the member states were free from BSE. In 2001, the EU regulated for the prevention, control and eradication of TSEs (Transmissible Spongiform Encephalopathies).

The Phillips Inquiry8 highlighted many significant errors in managing the BSE crisis. The following were particularly relevant to subsequent events:

"By the end of 1987 MAFF officials had become concerned as to whether it was acceptable for cattle showing signs of BSE to be slaughtered for human consumption. However, the Department of Health (DH) was not asked to collaborate with MAFF in considering the implications that BSE had for human health. It should have been"

"Only in March 1988, by which time MAFF officials had advised their Minister that animals showing signs of BSE should be destroyed and compensation paid, did MAFF advise the Chief Medical Officer (CMO) Sir Donald Acheson of the emergence of BSE and ask him for his view of the possible human health implications".

On the CMO's advice, an expert working party was established and in 1989 this group published a report which concluded "that the risks posed by BSE to humans were remote and that no precautionary measures were needed other than those recommended by the Working Party".

Where the Phillips Inquiry was scathing about the UK government response to BSE as too secretive and reassuring, Canada and shortly thereafter, the US adopted a very open and transparent approach to its first BSE case in 2003. Hueston5 writes "The discovery of BSE in Canada and the US in 2003 demanded a third type of risk communication-crisis and emergency risk communication. Producers, the food industry and consumers were all rightfully concerned and upset. The discovery identified a real risk to animal and human health and (public) outrage was high. The key strategy for effective crisis and emergency risk communication is described by the US Centres for Disease Control and Prevention as Be first, be right, be credible. In other words, the most effective strategy is to tell people what you know, what you don't know, what is being done to answer the outstanding questions, when you'll get back to them with more information and with the information currently available, what they can do to protect themselves, their families, their communities and their livelihoods."

An excellent example of this strategy was provided by the Canadian Chief Veterinary Officer, Dr. Brian Evans, as he dealt with the identification of BSE in Canada in May 2003. Dr. Evans responded directly to the media as soon as the disease was confirmed, providing daily press conferences with unlimited access through teleconference for reporters to join and ask questions. Each day he would review what was known, acknowledge what still was not understood, provide an update on the investigations, share guidance for consumers, producers and the food industry and remind participants of the next press briefing. His openness and candour elevated his credibility and blunted any potential criticism of secrecy or cover-up. This approach was adopted by the US seven months later when the US had its first outbreak.

Because active monitoring in the EU was limited prior to 2001, analysis of positive case statistics before that date needs to be undertaken with caution3. Nevertheless, the prevalence of BSE since 2001 (ratio of the number of BSE cases per 10,000 tested) highlights the dramatic reduction of disease rate (Figure 1).

In absolute number terms, the UK registered 8 cases of BSE in 2011, compared to a peak of about 35,000/year in the early nineties3.

From 1994, 176 cases of vCJD have been reported in the UK, all of whom have died1. In 2011 there were two new vCJD cases reported and 5 deaths. The vCJD "epidemic reached a peak about the year 2000 where there were 27 diagnoses and 28 deaths and has since declined to the current incidence of about 1 to 2 diagnoses/deaths per year"1.

Graph of BSE prevalence
Figure 1. Evolution of the prevalence of BSE in the 27 EU Member States since 2001 (ratio of the number of BSE positive cases per 10,000 animals tested)3

In his excellent review Hueston5 wrote: "BSE provides an example of an emerging infectious disease that demonstrates the challenges of policy-making in the face of rapidly changing science and public outrage pushing for action. Lessons learned through the BSE epidemic include: (1) beware of facts as new science continues to emerge; (2) complex issues rarely have simple solutions; (3) evaluate epidemics from a macro-epidemiologic perspective to understand their complexity and devise effective risk management strategies; (4) options always exist for prevention/control; (5) risk communications play a vital role before and during an emerging disease epidemic; and (6) risk management progress involves both science and politics. Adoption of One Health approaches involving systems thinking and shared leadership hold the most promise for effectively managing complex emergency global health issues like BSE".

Hueston5 looks at the lessons from the BSE outbreak and arrives at some very interesting conclusions eg. Scientific fact can be represented as dogmas when in fact they simply represent the best available hypothesis (at the time). BSE demonstrates evolving science, where dogma was later disproven or revised as more evidence emerged on causation, host specificity and distribution.

With such a positive story of disease reduction success, will the National TSE Surveillance Program (NTSESP)4 and equivalent programmes in other countries be short lived? According to EFSA (European Food Safety Authority) "Given our insufficient knowledge about the true prevalence of atypical animal prion strains in the field, it will be important to continue, and improve the systematic surveillance of animal TSEs, and to refine our diagnostic and laboratory methods .. it will be prudent to stay vigilant, although this must be in a way that is balanced with other risks to human and animal health"2.

In summary, TSE disease identification, prevention and eradication efforts will persist and most importantly, the ban on feeding animal material to ruminants will continue.

References

  1. Andrews NJ, 2011. Incidence of variant Creutzfeldt-Jakob disease diagnoses and deaths in the UK. January 1994 - December 2010. Health Protection Agency, Centre for Infections, Statistics Unit. Available from www.cjd.ed.ac.uk/
  2. Budka H; Editorial: The European Response to BSE: A Success Story. EFSA Journal 2011;9(9): e991. Available online www.efsa.europa.eu
  3. Report on the monitoring of ruminants for the presence of Transmissible Spongiform Encephalopathies (TSEs) in the EU in 2011. Publications Office of the European Union 2012 - 69 pp. ISBN 978-92-79-25859-6, ISSN 1725-583X Catalogue Number ND-AB-12-001-EN-C
  4. National TSE Surveillance Program (NTSESP), National Guidelines for Field Operations, JULY 2012 TO JUNE 2013, Animal Health Australia. Available from www.animalhealthaustralia.com.au
  5. Hueston, W.D. BSE and variant CJD: Emerging science, public pressure and the vagaries of policy-making. Preventive Veterinary Medicine 2013;109(3-4):179-184
  6. Pruisner, S. Novel proteinaceous infectious particles cause Scrapie. Science 1982;216:136-144
  7. Wells, G. Hawkins, S. Green, R. Austin, A. Dexter, Ll. Spencer, Y. Chaplin, M. Stack, M. Dawson, M. Preliminary observations on the pathogenesis of experimental bovine spongiform encephalopathy (BSE): an update. Vet. Rec 1998;142:103-106
  8. The BSE Inquiry: The Report. Inquiry into BSE and variant CJD in the United Kingdom, Available on line webarchive.nationalarchives.gov.uk

 

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