Circoviruses are circular, single-stranded DNA viruses and the smallest known autonomously replicating viruses.1 Two species of circovirus are known to infect pigs: porcine circovirus type 1 (PCV1) – which has not been associated with clinical disease – and porcine circovirus type 2 (PCV2), which was first isolated and characterised in the late 1990s. PCV2 has been associated with a number of disease syndromes in pigs worldwide, including post weaning multisystemic wasting syndrome.2 Before the introduction of PCV2 vaccination, it was one of the most damaging diseases affecting the pig industry and caused substantial economic …