Transmissible spongiform encephalopathies variants

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). 

This working party considers the aspects of the manufacture and control of biotechnological and biological medicinal products and is also involved in the provision of scientific advice. Workshops on the applieation of assays for markers of transmissible spongiform encephalopathies (TSE) and on the potential risk of transmitting new variant Creutzfeld-Jakob disease (nv-CJD) through plasma-derived medicinal products have recently been held. 

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. 

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). 

Two advisory committees of the US FDA, the Transmissible Spongiform Encephalopathies Advisory Committee and the Vaccines and Related Biologicals Product Advisory Committee, said at a joint meeting on 3 August 2000 that vaccines made from bovine-derived materials from countries with a known or uncertain risk of BSE carry only an infinitesimal risk of new variant Creutzfeldt-Jakob disease, and that no change in US immunization practice is indicated (Evans G, personal communication, 3 August 2000). 

Prion diseases In the 1990s, four patients were infected with variant Creutzfeldt-Jakob disease (vCJD) after transfusions of non-leukodepleted blood. The incubation periods in the recipients were 6.5-8.3 years after transfusion. Leukocytes are now removed from blood used for transfusion [60, 96, 9T]. Plasma products carry a low risk of transmission of transmissible spongiform encephalopathies because of production processes [96 ]. The estimated risk depends on the prion load. Of plasma products, vCJD-implicated batches of clotting factor concentrates were categorized as likely to transmit prion diseases [9T]. In the UK, and before the exclusion of the use of British plasma, the risk of prion transmission by blood was estimated to be 7-14 per 10000 patients with hemophilia, assuming a vCJD population prevalence of 1 in 10000... 

Not listed in Box 25.2 is the zoonosis arising from bovine spongiform encephalopathy (BSE), or mad cow disease . There is no conclusive evidence that the transmissible spongiform encephalopathies of man are acquired from animals, but the occmrence of so-called new variant Creutzfeld Jakob disease in man that has coincided with an epidemic of mad cow disease in cattle and related species has led to the... 

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. 

However, the emergence of variant Creutzfeldt-Jakob disease (vCJD) in the UK and France has raised concern about a new theoretical risk of infection in patients treated with blood and blood products (198). Animal experiments in which blood from sheep infected with bovine spongiform encephalopathy and natural scrapie-infected sheep into scrapie-free recipient animals have suggested disease transmission by the blood transfusion route in 2 of 24 sheep with bovine spongiform encephalopathy and in 4 of 21 sheep with scrapie (199). Many European countries have incorporated leukodepletion of all blood products, as leukocytes are believed to play a key role in the pathogenesis of variant Creutzfeldt-Jakob disease (198). In some countries, people who have lived in the UK for a period longer than 6 months between 1980 and 1996 are excluded from blood donation (13). Furthermore, it has been shown that various steps used in the manufacture of plasma-derived products also contribute to reduced infectivity by bovine spongiform encephalopathy (198). 

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