What is CJD?
Creutzfeldt-Jakob Disease is a neurodegenerative disease whose symptoms include dementia, cortical blindness, motor disorders, rigidity, muscle spasms and uncontrollable trembling, although it evokes no apparent immune or inflammatory response. There have been no documented recoveries: the disease usually causes death within six months of the onset of the symptoms. Creutzfeldt-Jakob disease occurs on a worldwide basis, with twice as much incidence in urban environments than in rural ones, with approximately one victim per million population while the peak age of occurrence is 60-65 although there are several examples of earlier onset.
Approximately 15% of cases appear to be caused by inheritance and these demonstrate an autosomal dominant pattern of gene expression. The remainder of cases are sporadic and have no obvious cause although there appears to be some clustering in certain ethnic groups such as Libyan Jews and Czechoslovakian herdsmen implying that contact with infected sheep herds may contribute to the incidence of the disease. However, the mechanism which causes sporadic cases of the disease is not known at present although some researchers feel that genetic susceptibility is to blame.
Creutzfeld-Jakob Disease has also been transmitted through surgical contamination: prions, the accepted causative agent of Creutzfeldt-Jakob disease have been found in brains, spinal cords, cerebrospinal fluid, tissue fluid and blood. However, researchers have recently cast doubt on the accepted theory that prions are the cause of CJD and BSE. It is not yet certain whether the disease can be transmitted through lactation but it is certainly able to be transmitted through blood transfusions. Until recently, diagnosis of Creutzfeldt-Jakob disease was impossible without a brain biopsy, but the new technique of two-dimensional electrophoresis can provide accurate tests, eliminating the misdiagnosis of Creutzfeldt-Jakob disease as Alzheimer's disease.
Until the identification of nvCJD (new variant CJD), in 1996, the disease was thought to exist in only three forms.
Sporadic cases, accounting for 85-90% of CJD cases.
Familial cases, making up 5-10% of all CJD cases.
Iatrogenic cases resulting from the accidental transmission of the causative agent via contaminated surgical equipment and comprising 1-5% of all CJD cases.
Evidence for an nvCJD-BSE link
The question of a link between nvCJD and BSE first arose because both of these TSEs became wide-spread at the same time. Recent scientific evidence which supports the link, includes the identification of deterioration in the brains of monkeys which have been inoculated with BSE, which is similar to that observed with nvCJD. An nvCJD-BSE link is further supported by the demonstration that nvCJD is associated with a molecular marker distinguishing it from other forms of CJD and resembling that resulting from BSE.
The most recent and powerful evidence comes from studies showing that the transmission characteristics of BSE and vCJD in laboratory mice are almost identical, strongly indicating that they are due to the same causative agent. The most likely cause of nvCJD is therefore exposure to the BSE agent, probably due to dietary contamination with nervous tissue from infected cattle.
Was it necessary to ban the consumption of beef on the bone to reduce the incidence of CJD?
Since 1997, approximately 170,000 cases of BSE have been found among British cattle as a result of feeding cows with the remains of other animals. About 20 cases of nvCJD have surfaced over the same period and in 1997, the British Government announced a ban on the sale of beef on the bone because of the possibility of consumers contracting the disease. However, even if a link between BSE and CJD were established, the risk to the public remains minimal: the Spongiform Encephalopathy Advisory Committee (SEAC) explained that without governmental action, there was a 5% chance that one person in the UK would contract nvCJD each year from eating beef on the bone. This meant that the probability of a Briton conracting nvCJD was approximately one in a billion: 40,000 times less likely than the probability that they would die ingesting carcinogens from eating potatoes. Since this law was not, therefore, necessary to protect public health, it is unclear why it was introduced and appears to have been entirely unnecessary.
However, as The Oolong Man points out, the SEAC's figure is only an estimate. Therefore it is still uncertain
Whether it is possible for people to contract nvCJD from BSE infected beef
How probable this event might be
How long the typical incubation period might be.
Although it seems unlikely, since the feedstock containing the causative agent of BSE has been removed from the food chain, it is still potentially possible for the incidence of CJD to increase among the population.