Prion diseases
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SPONGIFORM ENCEPHALOPATHIES (PRION DISEASES)

1. Human transmissible spongiform encephalopathies (including Creutzfeldt-Jakob (C-J) disease and kuru) have been transmitted to primates and to other animals through cell-free injections of infected brain tissue. Spongiform encephalopathies occur in several mammalian species. Scrapie affects sheep, and bovine spongiform encephalopathy occurs primarily in cows. Kuru, which affects humans, is associated with cannibalism in New Guinea natives. C-J syndrome and Gerstmann-Straussler-Schenker syndrome, which affect humans, appear to occur through both genetic and infectious routes, as known for scrapie.
The infectious agent has been characterized and is resistant to inactivation by ultraviolet radiation, formalin, heat and enzymes which denature nucleic acids. It can be inactivated (i.e. its infectivity destroyed) by proteases and other treatments that denature proteins.
The term "prion" was used to describe this small proteinaceous infectious particle. Abnormal forms of the prion protein (a ubiquitous protein of unknown function) cause these neurodegenerative diseases.
The disease occurs when the normal cellular prion protein undergoes a conformational change to the abnormal form. This may occur spontaneously at an extremely low rate or at a higher rate if there is a defect in the gene. The agent can "replicate" when the abnormal form crosses the path of the normal, cellular prion protein and the abnormal prion induces the normal form to adopt a similar abnormal form.


MORE INFORMATION: http://www.nmia.com/~mdibble/prion.html

OR http://www.kcc.com.msu.edu/CAI/Pathology/CNS_Infections_F/CNS_2a.html