Question: What are viroids?

Sally Cutler answered on 17 Nov 2014:

Dear Emma-Jane, thanks for coming back to me. A viroid is like a pathogenic short streatch of RNA. Most of those known so far are plant pathogens, but one has been found to date that causes human infection. This is hepatitis D which was originally thought to be a defective virus, but further investigation has shown that this is a viroid (RNA strand) enclosed within the outer shell of a hepatitis B virus (capsid), so like an infectious partical that has taken over the hepatitis B virus. Structurally this is a circular single strand of RNA