Molecular Detection and Sequence Analysis of Porcine Circovirus Type 3 in Sow Sera from Farms with Prolonged Histories of Reproductive Problems in Hunan, China

A newly emerging porcine circovirus, designated PCV3, has been reported in various countries (USA, Poland, South Korea and China) since 2017. Its presence may be associated with porcine dermatitis and nephropathy syndrome (PDNS), reproductive failure, and multisystem inflammation. In this study, we report identification of PCV3 in cases of reproductive failure in various regions in Hunan, China. From January 2015 to December 2016, sera were collected from 190 sows from seven farms with reproductive problems. Specifically, 85 samples were from sows with a history of reproductive failure, whereas the remaining 105 were from healthy sows. The PCV3-positive rate was significantly higher in sows with reproductive failure (45.9%) than in healthy sows (21.9%), based on quantitative PCR (qPCR) assays. Although phylogenetic analysis based on the cap gene suggested that these PCV3 isolates belonged to the clade PCV3a, amino acid sequence variations in the Cap protein still occurred among these isolates, and these might have contributed to antigenic alterations of the Cap protein, based on the Jameson-Wolf antigenic index. Finally, we concluded that PCV3 was circulating in sows in Hunan province, China. However, the association of PCV3 with reproductive failure in sows and its potential for vertical transmission need to be studied further.