Porcine circovirus 1 (PCV1) is a single-stranded DNA virus that is non-enveloped with an unsegmented circular genome roughly 1.7-1.8 kb in length. PCV1 belongs to the family Circoviridae and represents the first member of the genus Circovirus of which there are four known variants. First identified in 1974, PCV1 readily infects but is not known to cause disease in swine.