Difference between Viroids and Prions

Viroids are small, naked infectious RNA molecules. The term viroid was coined by T.O. Diener (1971) to describe the causal agent of the potato spindle tuber disease.

Prions are infectious protein particles causing neurological degenerative diseases in humans and animals. Stanley B. Prusiner discovered prions.

Viroids vs Prions 

          Viroids:

1. It is an infectious RNA particle

2. Viroid is formed of only small single stranded circular RNA

3. A protein coat is absent. 

4. Viroids are inactivated by ribonuclease digestion but resistant to proteinase K and trypsin digestion

5. Viroid has a smaller size than viruses

6. Viroid infects only higher plants (Exception: hepatitis D virus in humans is similar to viroid)
Common plant diseases include Potato Spindle tuber disease, Chrysanthemum stunt disease. 

Prions: 

1. It is an infectious protein particle 

2. It is formed of only proteins 

3. RNA or DNA is absent 

4. Prions are inactivated by proteinase K and trypsin digestion but resistant to ribonuclease treatment 

5. Mostly, smaller than viroid 

6. Prions infects animals causing neurological degenerative diseases 

‘Mad cow disease’ (Bovine spongiform encephalopathy) in cow and Scrapie disease in sheep and goat. 

Creutzfeldt-Jakob Disease (CJD), Kuru and Gerstmann-Strausler-Sheinker syndrome in humans.