Variant Creutzfeldt-Jakob disease (vCJD) belongs to a family of diseases that affects both humans and animals. This family of diseases is called transmissible spongiform encephalopathies (TSEs). The most common animal TSEs are scrapie (seen in sheep and goats) and bovine spongiform encephalopathy (seen in cattle). The disease-causing agent in TSEs is thought to be an abnormal form of the prion protein. The normal form of a prion protein is present in high concentrations in the brain with smaller amounts in other parts of the body. Variant CJD was first described in 1996 by the National CJD Surveillance Unit in Edinburgh and it has been shown that it can be caused by eating meat and/or meat products which contain the bovine spongiform encephalopathy agent. It is a fatal disease, which brings gradual and relentless damage to the neurones and which lasts for many years. This early phase is followed by personality changes, behavioural problems, poor co-ordination and progressive dementia. Death usually occurs within two years of these symptoms appearing.

In contrast to other forms of CJD, the abnormal form of prion protein in vCJD is also found in body tissues other than the brain and these include the tonsils and appendix. The protein has been found in the tonsils and appendix several years before the onset of symptoms. To discover how many people may be incubating vCJD, a study was set up to look for the presence of the abnormal prion protein in tonsils and appendices surgically removed during the late 1990s. The study was conducted by researchers at the Derriford Hospital in Plymouth and at the National CJD Surveillance Unit in Edinburgh. The study required that the tonsils and appendices were treated anonymously so that the name of the patient from whom they were taken was not known, but the majority of samples came from people aged 20-29 years of age. Of the 12,674 samples investigated three of them showed the presence of the abnormal form of the prion protein. If this figure is projected and applied to the whole population of the UK it suggests that approximately 3800 people in the United Kingdom may be incubating vCJD. In the view of these findings The Health Protection Agency is undertaking a larger study of 100,000 tonsils in order to refine this figure.