As I understand it, prions are just an ever-present rare tiny probability of a cascading malfunction of your physical composition. They are rare because they n

As I understand it, prions are just an ever-present rare tiny probability of a cascading malfunction of your physical composition. They are rare because they need to be, in order for a biological system to survive. (any biological system that had a high probability of prions would die off) They can never fully be eliminated because your body is built on probability, not mathematical certainty. Most organisms live less than 100 years, so the probability is good enough not to affect species survival. As long as young organisms don't eat old organisms, the chances remain low. Another way to look at it is that the combined lifespans of the organisms of a food chain are shorter than the time it would take for one mis-folded protein to be likely to occur and then also cascade to a degree that would affect the health of the top organism. Prion diseases only show up when you introduce a loop in the food chain.