VCJD

If the source of the infechon persists, after onset, then the incidence of new cases is maintained at a level which is commensurate with the infechvity of the pathogen and the ffequeney of exposure of individuals. In this manner, if cases of the variant Creutzfeldt-Jacob disease (vCJD), first recognized in the mid-1990s, relates to human exposure to bovine spongiform encephalopathy-infected beef in the early 1980s, then... 

Fig. 3. Classification of human prion diseases. Sporadic the transformation from PrPc (circle) to PrPSc (square) occurs without apparent cause. Familial a point mutation ( ) is thought to facilitate the transformation. Infectious the transformation arises via PrPSc which acts as a template. The kinetic equations are defined by Eigen (1996). The infectious form includes kuru, iatrogenic CJD (iCJD), variant CJD (vCJD first reported in 1996), bovine spongiform encephalopathy (BSE first reported in 1985), and scrapie. In the nucleation-dependent model, monomeric PrPc and PrPSc are in chemical equilibrium.

Transmissible spongiform encephalopathies (TSEs)—Brain diseases transmitted from one animal to another. Under a microscope, the brain tissue of animals and people with TSEs resembles a sponge. TSEs include variant Creutzfeldt-Jacob disease (vCJD) in humans, scrapie in sheep and goats, and bovine spongiform encephalopathy (BSE) in cows (mad cow disease). These diseases are spread by consumption of brain tissue and are thought to be caused by prions, a kind of protein. 

Because they are derived from cattle, there is a concern that gelatins might be vehicles for the transmission of the prion agent responsible for bovine spongiform encephalopathy (BSE) in cattle and variant Creutzfeldt-Jakob disease (vGD) in humans. There is at present no evidence that these products have contributed to the transmission of BSE or vCJD. However, the incubation period may be up to several years, and due prudence is warranted when such products are used. 

Brain tissue of a patient infected with vCJD. Note the formation of (white) vacuole spaces and (dark, irregular) plaques of prion protein. (Magnification 200X)... 

In human populations, exposure to the BSE agent (probably in contaminated bovine-based food products) has been strongly linked to the 1996 appearance of a new transmissible spongiform encephalopathy of humans called variant Creutzfeldt-Jakob Disease (vCJD). 

A new human transmissible spongiform encephalopathy, variant CJD or vCJD, is identified and distinguished from classic CJD. The UK bans the use of mammalian MBM in feed for all farm animals. The UK introduces slaughter scheme to keep cattle older than 30 months out of food and feed chains. Cattle passports are made mandatory for all cattle bom beginning July 1, 1996. The United States FDA imposes a ban on feeding MBM protein to mminants (36). 

The first confirmed case of vCJD in North America is reported in a man in Saskatchewan, Canada. EU issues regulations under Directive 1774/2002 setting out a system for handling Animal Byproducts (ABPR). 

The sCJDWl subtype has W at PrP codon 129 and type 1 PrP % and it accounts for 1% of the sporadic cases. The mean age at onset is 39 years and the mean clinical duration is 15 months. This younger age of clinical onset is unusual for a sporadic human prion disease and more closely resembles the age of onset that is characteristic in vCJD. This subtype shows dementia at the early clinical stages and is followed by myoclonus and pyramidal signs. There is no PSW on EEG and the CSF 14-3-3 is positive in all cases tested. 

Iatrogenic CJD is the second most common acquired human prion disease and these cases are the result of accidental infection due to contact with prion contaminated tissues or instruments during medical procedures (Table 29.1). The mode of prion infection include surgical equipment (e.g., surgical insd uments, depth electrodes), transplantation of human tissues (comeal, dura mater), intramuscular injections with growth hormone or gonadotrophin extracted from human pituitary tissues, or blood transfusion (reviewed by Will, 2003). The most likely source of infection is from donors with subclinical sCJD, except for the tw o transfusion-related cases that have been linked to blood donors who developed vCJD several years later (reviewed by Ironside, 2006). The incubation period in these transfusion related cases was 5 to 6 years, v hich is shorter than primary vCJD infection in humans. 

PrP " deposition in the central nervous system is also a hallmark feature of prion disease (Prusiner, 1991). The type of Prpsc cleposit and its location varies among the human prion diseases. PrP is also a component of amyloid plaques. A characteristic of vCJD and kuru is florid amyloid plaques, which is a large cluster of PrP aggregates interspersed with vacuolar pathology. PrP deposition is also present in peripheral tissues of patients with vCJD, primarily in secondary... 

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