Theory:

Prions are not microbes. They are not alive, neither grow nor reproduce.
Prion is a kind of a protein that triggers normal proteins to misbehave (or misfold) in the brain.
Prions may affect both humans and animals.
  • Prions get into the human system by consuming infected meat products. Creutzfeldt-Jakob disease popularly known as -CJD is caused due to prions in human beings.
  • Recent researches even link the diseases like Alzheimer’s and Parkinson’s diseases to prions.
  • In cows, prions are linked to mad cow disease, which leads to a slow degeneration of the brain and becomes fatal to cows life.
Prion.jpg
A prion
 
Virions are virus particles found outside the cells.
Once if a virion gets into a host, it becomes a virus and starts multiplying and infecting the host.
Reference:
Image credit:
Prion: Free image from Wikipedia; https://commons.wikimedia.org/wiki/File:BOVINE_PRION_PROTEIN_1dx0_asym_r_500.jpg