Unusual Infectious Agents

Question 1

Why are prions not considered related to viruses?

Answer 1

Prions do not have any nucleic acid

Question 2

What is a viroid?

Answer 2

smallest known pathogen

single-stranded RNA molecules that do not produce mRNA or proteins, just replicate autonomously

infect plants - plants have microchannels between cells, which easily allows transfer of viroid, and propagate infection. Animal cells require fusion, or exocytosis to release a viroid, so infection cannot take hold in animals

Question 3

What is a satellite virus?

Answer 3

Incomplete virus, which is dependent on a helper virus for reproduction

e.g HDV

Question 4

What are the types of CJD?

Answer 4

Sporadic - new mutation

Familial - inherited mutation

Variant - ingestion of infected meat e.g BSE

Question 5

Viroids, satellites and prions all have ciruclar RNA

What is benefit of this?

Answer 5

Linear RNA is at risk of information loss from ends of linear genome