Prion

Prions are a type of disease causing agent which consist of a protein which can cause other similar proteins to take its shape. As such, they can make copies of themselves without the need for DNA, as is the case with bacteria and parasites, or the RNA used by many viruses. They were first theorized in the 1960s to explain certain types of brain altering diseases which could not be traced to any other cause. Their existence was finally proven in 1982 and won the Nobel Prize for their discoverer Stanley B. Prusiner in 1997.
Prion diseases can be transmitted from person-to-person or have a genetic cause, but they're all very rare, terminal, and difficult to contract. The three human diseases that have been proved to be caused by prions are:
*Creutzfeldt-Jakob disease, a brain wasting disease, which can apparently be contracted by eating meat contaminated with brain prions from Mad Cow Disease or Scrapie (found in sheep).
*Kuru, or laughing sickness, known only in New Guinea among peoples who ate the remains of deceased family members
*Fatal familial insomnia, a genetic illness that causes intractable insomnia.
Prion at Wikipedia
Category:Physiology