BSE controls final report, 20 December 2000, section 3, Relationship between vCJD and BSE

7. Both BSE and vCJD are diseases characterised by the appearance of abnormal prion protein in neural tissues. The distribution of susceptibility to BSE within mammals remains a puzzle; dogs, for example, do not appear to have been affected, whilst over 80 cases have been reported in domestic cats. These diseases, which are known to occur in a number of different groups of mammals, see Table 1 below, are characterised by long asymptomatic incubation periods followed by progressive symptoms and signs of degeneration of the brain, leading eventually to death. They get their name, Transmissible Spongiform Encephalopathies (TSEs), from the spongy appearance in the infected brain, and the fact that they are transmissible via infected material. Remarkably, the agent thought by most scientists to cause the disease is not a conventional infective microorganism such as a virus or a bacterium but an abnormal form of protein, called a prion protein. The detailed function of the normal prion protein is not known. However, according to the prevailing current view, infection of the body with an altered form of the protein, sometimes called abnormal prion protein, can cause the body’s own normal prion to reshape to the altered form which, instead of serving its usual function, eventually accumulates within the brain and directly or indirectly causes degeneration.

TABLE 1: The Transmissible Spongiform Encephalopathies

Host	Disease
Man	Creutzfeldt-Jakob Disease - sporadic - familial - iatrogenic - variant* Gerstmann-Sträussler-Scheinker syndrome Kuru Fatal Insomnia, familial and sporadic
Sheep, goat, moufflon	Scrapie
Farmed mink	Transmissible Mink Encephalopathy
Mule/Whitetail deer and Rocky Mountain elk	Chronic Wasting Disease
Domestic cattle	Bovine Spongiform Encephalopathy*
Domestic cat	Feline Spongiform Encephalopathy*
Kudu, gemsbok, nyala, oryx, eland, cheetah, puma, tiger, ocelot, bison, ankole cow, lion	Spongiform encephalopathies* that have occurred contemporaneously with the BSE epidemic

* Note. Biologically indistinguishable strains of TSE agent have been recovered from cases of BSE, variant CJD, feline spongiform encephalopathy and from cases of spongiform encephalopathy in kudu and nyala.

8. On 20th March 1996 SEAC reported that 10 cases of a new variant of the human TSE, Creutzfeldt-Jakob Disease, had been described, affecting mostly young adults. The new disease, diagnosed from clinical history and through study of the pattern of degeneration of the brains of dead victims, was named new variant CJD, now called variant CJD (vCJD). SEAC concluded that the most likely origin of the new disease was exposure to the BSE prion as a consequence of eating beef products contaminated with the BSE agent¹. The Secretary of State for Health made an announcement to Parliament which was followed by a Statement from the Minister of Agriculture, Fisheries and Food that controls in place at that time, on beef and beef products entering the food chain, would be strengthened.

9. vCJD differs from classical or sporadic CJD, in that it occurs predominantly in a younger age group, causes different changes in the nervous tissues, and has, on average, a more prolonged clinical course than the classical form of the disease. It had always been hypothesised that if exposure to BSE were to cause disease in humans, then that disease would most likely resemble CJD². Whilst the likely link between exposure to BSE and the occurrence of vCJD was considered by SEAC and Ministers as sufficient to justify action, nevertheless the evidence was and remains circumstantial, albeit strong. It will have to remain so because there must be a complete ethical bar to a human transmission experiment capable of providing conclusive evidence.

10. The further scientific evidence that has appeared since March 1996 supports SEAC’s conclusions. In particular Bruce et al³ have shown that the pattern of brain lesions and the incubation periods in different strains of mice are essentially identical for BSE and vCJD when the mice are injected with infected brain material. In addition, Collinge et al⁴ demonstrated that the biochemical fingerprint of the prion agent causing vCJD was the same as that for BSE and different from that for the sporadic CJD agent. SEAC keeps the results of further research in this area under constant review and its most recent statements⁵, after considering all available information, conclude that there is compelling evidence that the two agents are the same and that the most likely explanation for the vCJD cases to date is exposure to the BSE agent.

11. The Government has set in place a large research programme on TSEs at a cost of some £70 million since April 1997. A further £29 million is planned for projects underway in 2000/01⁶. The total spend on TSE related research since 1986, when BSE was first recognised as a problem, is in excess of £140 million. Unfortunately, the time taken for most animal experiments with prions to produce a result is at least a year, and can be much longer. This means that we have to accept that decisions on the management of the epidemic and the protection of the health of the public will continue to be based on an incomplete understanding of the science and will need to be informed by expert judgements for many years to come.

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1 - Statement to Parliament by Secretary of State for Health 20 March 1996

2 - Will RJ et al (1996) A new variant of Creutzfeldt Jakob Disease in the UK, Lancet, 347 921-925 (1996)

3 - Bruce et al, Transmission in mice to indicate that the ‘new variant’ CJD is caused by the BSE agent. Nature, 389 498-501 (1997)

4 - Collinge et al, Molecular analysis of prion strain variation and the aetiology of ‘new variant’ CJD, Nature, 383 685-690 (1996)

5 - SEAC Press Releases, Department of Health Press Release 139/99: Summary of Spongiform Encephalopathy Advisory Committee meeting 18 March 1999