Variant Creutzfeldt-Jakob disease
- Variant Creutzfeldt-Jakob disease (vCJD) is a rare and fatal human neurodegenerative condition.
- The consumption of food of bovine origin contaminated with the agent of Bovine Spongiform Encephalopathy (BSE), a disease of cattle, has been strongly linked to the occurrence of vCJD in humans.
- 175 cases of vCJD were reported in the United Kingdom of Great Britain and Northern Ireland (United Kingdom), and 49 cases in other countries from October 1996 to March 2011.
- Following the successful containment of the BSE epidemic in cattle, the number of cases of vCJD in the United Kingdom has declined since 2000.
Variant Creutzfeldt-Jakob disease (vCJD) is a rare and fatal human neurodegenerative condition which is classified as a Transmissible Spongiform Encephalopathy (TSE) because of its ability to be transmitted and the characteristic spongy degeneration of the brain that it causes.
vCJD was first described in the United Kingdom in March 1996 and has been linked with exposure to a TSE of cattle called Bovine Spongiform Encephalopathy (BSE), also known as Classical BSE1, which was first reported in the United Kingdom in 1986.
From October 1996 to March 2011, 175 cases of vCJD have been reported in the United Kingdom, 25 in France, 5 in Spain, 4 in Ireland, 3 each in the Netherlands and the United States of America (USA), 2 each in Canada, Italy and Portugal, and one each in Japan, Saudi Arabia and Taiwan. The number of cases of vCJD in the United Kingdom peaked in 2000 with 28 deaths. It has since declined to about 2 diagnosed cases and 2 deaths per year in 2008.
Before the identification of vCJD, Creutzfeldt-Jakob disease (CJD), the most common of the known human TSEs, was thought to exist in only three forms:
- sporadic CJD, which occurs throughout the world at the rate of about one per million people, and accounts for about 85% of CJD cases;
- familial CJD, which is associated with a gene mutation and makes up 5–15% of CJD cases; and
- iatrogenic CJD, which results from accidental transmission via contaminated surgical equipment or as a result of corneal or meningeal (dura mater) transplants or the administration of human-derived pituitary growth hormones; this accounts for less than 5% of CJD cases.
In contrast to the traditional forms of CJD, vCJD has affected younger patients (median age at death of 28 years, as opposed to 68 years) and has a relatively longer duration of illness (median of 14 months as opposed to 4.5 months).
The first person to develop symptoms of what turned out to be vCJD became ill in 1994. Most people who have developed vCJD lived in the United Kingdom. Some cases that were diagnosed in countries other than the United Kingdom occurred in people who were probably exposed to the BSE while residing in the United Kingdom.
As of early May 2011, the CJD surveillance unit for the United Kingdom reported 172 primary cases of vCJD, and three secondary cases of vCJD related to blood transfusion. Among primary cases, there are four additional cases in the United Kingdom and one in Canada where vCJD is strongly suspected, but the diagnosis has not yet been definitively confirmed by post mortem analysis.
Early in the illness, patients usually experience psychiatric or sensory symptoms, which most commonly take the form of depression, apathy or anxiety, and occasionally (in a third of the cases) unusual persistent and painful sensory symptoms. Neurological signs, including unsteadiness, difficulty walking and involuntary movements, develop as the illness progresses and, by the time of death, patients become completely immobile and mute.
- The clinical presentation, progressive nature of the disease and failure to find any other diagnosis are characteristic of vCJD.
- There are no completely reliable tests to use before the onset of clinical symptoms. However, magnetic resonance scans and tonsillar biopsy are useful diagnostic tests.
- The brainwave pattern observed during an electroencephalogram is abnormal in most vCJD patients.
- Currently, the diagnosis of vCJD can only be confirmed following pathological examination of the brain post mortem. Characteristically, multiple microscopic and abnormal aggregates encircled by holes are seen in the brain tissue, resulting in a daisy-like appearance described by the term "florid plaques".
The nature of the vCJD agent is being investigated and is still a matter of debate. One prevalent theory is that the agent is composed largely, if not entirely, of a self-replicating misfolded protein, referred to as a prion.
There is strong scientific evidence that vCJD is linked with exposure to a TSE of cattle called BSE. The link between vCJD and BSE was first hypothesized because of the association of these two TSEs in time and place. In addition, laboratory evidence indicates that vCJD is linked causally with BSE.
Intensive surveillance in European countries has confirmed the high incidence of vCJD in the United Kingdom, the country with the largest potential exposure to BSE. Several cases in other countries were likely exposed to the BSE agent while residing in the United Kingdom.
The most likely cause of vCJD is exposure to the BSE agent through consumption of food from bovine origin most plausibly contaminated by infected bovine brain or other central nervous system tissue.
Only four cases of vCJD infection have been associated with blood transfusion: three of these cases developed symptoms of vCJD several years after transfusion, and one died from unrelated causes before developing symptoms of vCJD, but was shown to be infected with vCJD.
Measures taken to protect public health
- Due to the strong evidence of a link between vCJD and BSE, the UK government made BSE a notifiable disease in 1988. Since 1994, the European Union has progressively implemented control measures that have contained BSE. The main measures are detailed in the information sheet on Bovine Spongiform Encephalopathy.
- Since 1999, the United Kingdom has no longer sourced plasma from its inhabitants, and as a further precautionary measure against the occurrence of vCJD, has instituted leukocyte depletion (removal of white blood cells) from blood transfusions. Some countries have prohibited donations of blood from persons who have resided in countries with higher risk of BSE.
WHO has worked on:
- convening scientific consultations on issues related to animal and human TSEs (these meetings have made recommendations aimed at protecting human and animal health);
- assisting with global surveillance of CJD and its variants, by holding training courses worldwide, particularly in developing countries, to help countries establish national surveillance of CJD and its variants;
- convening the Technical Consultation on BSE: Public Health, Animal Health and Trade, publishing the WHO manual for surveillance of human transmissible spongiform encephalopathies, including variant Creutzfeldt-Jakob disease.
To protect human health, WHO has several recommendations.
- No tissue that is likely to contain the BSE agent, nor part or product of any animal which has shown signs of a TSE should enter the (human or animal) food chain. All countries should ban the use of ruminant tissues in ruminant feed.
- The pharmaceutical industry should avoid the use of bovine materials and materials from other animal species in which TSEs naturally occur. If their use is absolutely necessary, these materials should be obtained from countries which have a surveillance system for BSE in place and which reports zero cases of BSE.
- The Guidelines on tissue infectivity distribution in transmissible spongiform encephalopathies in 2006 provide information and assist national regulatory authorities in conducting risk assessments of vCJD transmission.
In 2010, WHO updated the Tables on tissue infectivity distribution in transmissible spongiform encephalopathies. The Tables reflect the current status of knowledge about infectivity in body tissues, secretions, and excretions of humans and animals, and thus provide information about potential transmission of vCJD through human blood and blood products, as well as through medicinal products prepared with animal-derived materials.
1 The term "Classical BSE" has been introduced to differentiate the disease from Atypical BSE cases, which occur rarely in the cattle population.