The prion is a Slow, subtle and extremely complex pathogen hidden inside the brain.
Prion is a standard game disease in Plague Inc. characterized by significantly altering the way neurons function, causing certain tasks to become much more complicated to perform such as research and cure development. 
The unique trait that Prion has in Plague Inc. is Neural Atrophy, which is like Genetic Hardening, slowing down cure research. Lethality from evolved traits will take longer to take effect.