Creutzfeldt-Jakob Disease (vCJD)
Department of Health (UK)
What is vCJD?
Both vCJD and BSE are relatively new forms of a family of diseases, known as transmissible spongiform encephalopathies (TSEs), that have been recognised for hundreds of years. They are called “spongiform” because, under a microscope, the affected brain tissue looks like a sponge.
TSEs can affect both people and animals and share common characteristics. All of them have long incubation periods which makes identification and prevention more challenging.
When BSE was discovered in cattle in the 1980s, scientists assumed it was similar to another common TSE called scrapie, which affects sheep and goats. Scrapie, first recorded in Britain in 1732, has been shown to be transmissible to several animal species in the laboratory, but never to people. A National Scrapie Plan was introduced in July 2001 which aims to eradicate the disease in sheep and goats.
TSEs are believed to be caused by the prion protein, which is found principally in the brain and spinal cord, although lower levels may be found in some lymphoid tissues such as the spleen and tonsils. In TSE-infected people or animals, these proteins have become altered to an abnormal form that appears to trigger a gradual degeneration of brain tissue. It is not known why this change occurs.
There are three types of human TSE. Classical or “sporadic” Creutzfeldt-Jakob disease (CJD) is the most common human TSE. The disease is still very rare, affecting only one person per million worldwide. It is referred to as ‘sporadic’ because there is no identifiable cause. It was first identified in the 1920s and typically affects the elderly. Familial CJD, in which there is a family history, occurs even more rarely, in about one out of 10 of all CJD cases.
The first cases of Variant CJD (vCJD) occurred in 1995, but it was not until 1996 that it was recognised as a new form of CJD. It is thought that vCJD in people has resulted from exposure to BSE, the most likely route being through the consumption of affected meat. An article published in The Lancet in April 1996 first provided evidence for the link. A Parliamentary Statement by the then Secretary of State for Health, Stephen Dorrell, on the link between BSE and humans, on 20 March 1996, marked the development of the BSE affair into a national public health crisis.
A major difference between the two main types of CJD is that vCJD occurs in younger people – the average age of death is around 29 years, compared to 65 years for sporadic CJD – and the period of illness is longer. Another difference is that in patients with vCJD, the abnormal prion protein has been found in lymphoreticular tissue such as the appendix and tonsils.
The early symptoms of vCJD often include anxiety, withdrawal and behavioural changes. As a result, many patients are first referred to a psychiatrist rather than a neurologist. This type of behavioural change is not uncommon in the general population, particularly in teenagers, and explains why early detection of the disease is so difficult.
Later on, the patient may experience pain and/or odd sensations in the limbs and face. After several weeks, the patient will start to suffer from further neurological symptoms, such as a ‘jerkiness’ of the limbs and a difficulty in walking. This is followed by a progressive dementia, such as memory loss, and the patient will often fail to recognise relatives or friends. Eventually, patients lose the ability to move or speak and need 24-hour care. On average, the disease claims the life of its victims a year after the first symptoms appear.
There is no simple test for CJD. Confirmation of the diagnosis depends on testing tissue from the brain, something that usually happens only at post-mortem, or – in the case of vCJD – a test of tissue from the tonsils, during the course of the disease. A positive tonsils test is considered definitive if it is supported by other symptoms, as part of a wider clinical picture.