Transmissible spongiform encephalopathies are a group of progressive conditions that affect the brain and nervous system of humans and animals and are transmitted by prions. Mental and physical abilities deteriorate and myriad tiny holes appear in the cortex causing it to appear like a sponge (hence ‘spongiform’) when brain tissue obtained at autopsy is examined under a microscope. The disorders cause impairment of brain function, including memory changes, personality changes and problems with movement that worsen over time. Prion diseases of humans include classic Creutzfeldt-Jakob disease, new variant Creutzfeldt-Jakob disease (a human disorder related to mad cow disease), Gerstmann-Sträussler-Scheinker syndrome, fatal familial insomnia and kuru. These conditions form a spectrum of diseases with overlapping signs and symptoms.

Unlike other kinds of infectious disease which are spread by microbes, the infectious agent in TSEs is a specific protein called prion protein. Misshaped prion proteins carry the disease between individuals and cause deterioration of the brain. TSEs are unique diseases in that their aetiology may be genetic, sporadic or infectious via ingestion of infected foodstuffs and via iatrogenic means (e.g. blood transfusion) (reviewed in Prusiner, 1991; Collinge, 2001).

These spontaneous disorders in humans are very rare affecting only about one person per million worldwide each year.

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