Unfortunately, there are several prion diseases already in existence: scrapie in sheep, BSE in cows, Chronic Wasting Disease in deer, and both Kuru and Crutzfeld-Jacob in humans.

Scrapie is incredibly durable in the environment; the prion toxins can remain transmissible in the soil for a decade, causing disease years after it was shed by its previous host.

https://en.wikipedia.org/wiki/Transmissible_spongiform_encep...