Prion diseases disrupt neurons in the brain in immense numbers, eventually leading to the death of the infected animal.
Prion diseases have several unusual features.
The infected animals do not mount any observable immune response. A protein called PrP, the prion, has been implicated as the infectious agent. The protein itself appears to be transmissible between animals, in the absence of any virus, bacterium, fungus or other known pathogen. The most common form of TSEs is scrapie, a disease that has been in Britain for at least 200 years and in the United States since 1947. The disease, found in sheep and goats, causes animals to lose coordination and eventually become so ill they cannot stand on their own.