Europe’s BSE and nvCJD crises

© 2004-2005 William Charteris
www.billcharteris.com
www.imperialconsulting.net

Prion diseases are a group of transmissible animal and human neurodegenerative diseases. They are uniformly fatal and characterized by a long incubation period and a multi-focal neuropathology involving spongiform changes, neuronal loss, astrogliosis, and the accumulation of the pathological or ‘structurally aberrant, protease-resistant’ conformers of the prion protein (PrP^res) in the brain and to a lesser extent in other organs. This toxic gain of function of an aberrant form of a constitutively expressed protein and associated failure to clear these proteins from the brain induces neuronal dysfunction and leads to death.

The most common human TSE is CJD, which is classified epidemiologically as sporadic or classic, familial, iatrogenic, and variant or new-variant. Even the most frequent form, sCJD, is very rare. It appears to be evenly distributed worldwide exhibiting an incidence of circa one individual per million per year. BSE is classified as a TSE, variants of which include scrapie in sheep and chronic wasting disease in deer and elk. In 1996, UK government scientists announced that the ‘‘most likely explanation” for 10 cases (median age, 28 years) of nvCJD was ‘‘exposure to BSE’’. nvCJD is distinguished from the sCJD by the much younger median age of affected patients, its clinical features and neuropathology, and the biochemical properties of the PrP^res. A recent estimate of the mean incubation period for nvCJD following consumption of an infectious dose of BSE-infected beef by a genetically susceptible individual (MM homozygote) is 16.7 years (95% confidence interval, 8–30 years).

The BSE epidemic, which began in the early 1980s, and the associated nvCJD epidemic are now, with high probability, in decline. Although 95% of cases occurred in the UK, the economic impact has been felt throughout Europe and will continue indefinitely. In present value terms, it is estimated at €100 billion with up to 10% of the annual value of beef output having been lost. Of prime importance has been the permanent damage to consumer confidence not just in beef, but in all foods. In addition, the reputation of the scientific establishment for providing objective and independent information has been severely damaged in the public mind, and government authorities have been perceived as protecting sectoral interests rather than the public in general.

Until the outbreak of the BSE crisis, Community regulation on food safety lacked a coherent concept of risk regulation. Nevertheless, the scientific committee-based food safety regulatory approach appeared to function generally well and both national authorities and the Commission were satisfied. However, the BSE epidemic shattered this confidence. The BSE crisis revealed deficiencies in beef industry practices, public food safety structures, and the ad hoc approach followed by the Community. It highlighted the need for a more conceptual, risk analysis-based approach to food safety regulation, a concept which explicitly recognizes that risk regulation is permeated by social and political considerations and is based on negotiation and deliberation with civil society.

Recent reports of secondary nvCJD transmission via blood products obtained from donors who were incubating the disease are of concern because of a potentially large number of blood donors who might have been exposed to BSE and may be infectious but clinically asymptomatic. The blood donor deferral policies instituted by blood transfusion agencies in Europe and elsewhere are expected to greatly minimize the risk of secondary transmission due to such low-level endemicity.

No proven treatment for human and animal TSE exists. Back-calculation modelling suggests the likelihood that almost 1·6 million infected cattle entered the human food chain during the BSE crisis. Treatment of animal by-products at 133^oC at 3 bar for a minimum of 20 min will destroy prions, but for food and blood products there are no ‘feasible’ processes to destroy the agent.

This abstract is taken from a paper entitled 'A critical review of the evolution of scientific advice to the Commission on food safety since the formation of the European Economic Community', which was published on December 6, 2004. The paper comprises 5,500 words and 47 references. Individual copies of the paper may be requested by e-mail from the author.