Novel circovirus species identified in farmed pigs designated as Porcine circovirus 4, Hunan province, China

In pigs, three circovirus species within the genus Circovirus have been identified so far, including the non-pathogenic Porcine circovirus 1 (PCV1), the pathogenic Porcine circovirus 2 (PCV2) and the recently identified Porcine circovirus 3 (PCV3). In April 2019, a new circovirus with a distinct relationship to other circoviruses was identified in several pigs with severe clinical disease in Hunan province, China. The size of the viral genome, tentatively designated as porcine circovirus type 4 (PCV4), is 1,770 nucleotides (nt). PCV4 shows the highest genomic identity to mink circovirus (66.9%) and has identities of 43.2%–51.5% to the other PCV genomes. Two major genes, a replicase (Rep) gene spanning 891 nt and a capsid (Cap) gene spanning 687 nt, were predicted. Furthermore, a TaqMan® real-time polymerase chain reaction (PCR) targeting the replicase gene was developed to investigate the prevalence of PCV4 in 187 clinical samples from Hunan province, China. The results revealed an overall PCV4 prevalence of 12.8%, with the highest positive rates in nasal swabs (28.5%, 6/21) followed by serum samples (13.4%, 11/82). The clinical significance and pathogenesis of this virus needs further investigation.