Is Circovirus DNA Infectious?

by Vincent Racaniello

Saturday, March 27, 2010 at 06:45 AM EDT

The US Food and Drug Administration does not want Rotarix, the rotavirus vaccine, to be used because it contains porcine circovirus 1 DNA. If complete copies of the circovirus genome were present, would they constitute a potential threat to recipients? Put another way, is circovirus DNA infectious?

Here is the information you need to answer this question.

• The circovirus genome is a circular, single stranded DNA molecule (pictured).
• To infect a cell, the two viral proteins encoded in the DNA must be produced.
• To produce proteins, mRNA must be synthesized from the viral DNA.
• Single-stranded DNA cannot be copied into mRNA; the DNA must be double-stranded.
• The circovirus particle consists of a protein shell surrounding the viral DNA. There are no other components in the virion.
• During infection of cells by circoviruses, the particles enter the nucleus where the viral DNA is released
• If naked DNA is added to cells, a good fraction ends up in the nucleus.

Knowing these facts, can you determine whether introduction of circovirus DNA into cells would lead to viral replication?