1.5 BSE and risks to human health: vCJD
Given this background, it is not surprising that the possibility that BSE in cattle might pose a health risk to humans was given serious consideration from a very early stage in the outbreak. Various precautionary measures intended to eradicate BSE in cattle and also to prevent any possibility of transmission of the disease to humans were introduced. We will discuss these in more detail later in the course. At the same time, the public was repeatedly assured by both officials (e.g. the Chief Medical Officer or CMO) and politicians (e.g. the Secretary of State for Agriculture, Fisheries and Food) that it was perfectly 'safe' to eat British beef (see Section 8). One of the reasons for this confidence was that humans had not contracted any TSEs from scrapie-infected sheep in more than 200 years. Although it was generally assumed that BSE would pose no greater threat to human health than had scrapie, it should be borne in mind that BSE was a new disease, the characteristics of which were by definition unknown. [C R D]
Nevertheless, following diagnosis during 1994 and 1995 of 10 cases of CJD in people under 42 years of age, variant (formerly, new variant) Creutzfeldt-Jakob disease (vCJD) was recognised as a new TSE in its own right. Although vCJD shares some clinical symptoms with other types of CJD, there are important differences. For instance, vCJD affects younger people (the average age at death is less than 30 years), has a longer duration (up to two years between onset and death) and has different early clinical symptoms (psychiatric or behavioural changes, such as depression, rather than dementia) than classical CJD.
The Secretary of State for Health stated in the House of Commons on 20 March 1996 that [C]:
There remains no scientific proof that BSE can be transmitted to man by beef, but the [scientific advisory] committee have concluded the most likely explanation at present is that these cases are linked to exposure to BSE before […] 1989.
By the end of 2004, there had been 148 deaths in the UK from confirmed or probable vCJD. Although current calculations suggest that about 200 UK residents will have died from this disease by the time the outbreak comes to an end, it will be many years before we know for sure. At one stage it was feared that the death toll would be very much higher than this (Section 5). There have also been a few cases of vCJD in other countries.
What then is the cause of TSEs, such as BSE and vCJD? To answer this question, we need to look at a relatively new area of scientific investigation: the biology of prions.