What Are Prions?

A prion is short-hand for proteinaceous infectious
particle. Prions are infectious proteins thought to
cause disease as viruses do (prions are misfolded,
misshapen, proteins). The key difference between a
prion and a virus is that prions lack the DNA or RNA
that forms the command structure of a virus. Prions
have been implicated with a number of diseases,
including scrapie, kuru (once called laughing
sickness), Creutzfeldt-Jakob disease, and in Bovine
Spongiform Encephalopathy (BSE) (the so-termed
Mad Cow Disease). Mad-cow disease involves prions
which have been passed between cattle by eating
feed containing (or contaminated with) brain matter
from infected animals, and can then be passed on to
humans who eat the similarly contaminated meat of
infected cattle. There was an outbreak of this disease
in British cattle in the 1980s.
The prion proteins contradict a central tenet of
molecular biology: that genes affect proteins, but
proteins do not affect DNA. To date, any known
disease transmitted by prion is untreatable. Prions
attack the nervous system, particularly the brain.
Once in an animal's brain cells, proteins near the
prions apparently begin to deform and refold
themselves to match the defective prion. In sheep,
scrapie-infected animals stagger and die as their
brains disintegrate. With BSE, humans suffer a
hideously similar fate.