Transmissible spongiform encephalopathies (
TSEs), also known as
prion diseases, are a group of progressive conditions that affect the
brain (
encephalopathies) and
nervous system of many
animals, including
humans. According to the most widespread hypothesis, they are transmitted by
prions, though some other data suggest an involvement of a
Spiroplasma infection. 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 (nvCJD, a human disorder related to
Bovine spongiform encephalopathy),
Gerstmann–Sträussler–Scheinker syndrome,
fatal familial insomnia,
kuru, and the recently discovered
Variably protease-sensitive prionopathy. These conditions form a spectrum of diseases with overlapping signs and symptoms.