Detection and genetic characterization of porcine circovirus 4 (PCV4) in Guangxi, China

Porcine circovirus type 4 (PCV4), a novel circovirus, was first detected in pigs with porcine dermatitis and nephropathy syndrome (PDNS) in China. This study investigated the frequency of porcine circovirus 4 (PCV4) in pigs in Guangxi Province, China, from 2015 to 2019 and its genome diversity. Thirteen of 257 (5.1%) samples were positive for PCV4, 9 of 13 (69.2%) PCV4-positive samples were coinfected with PCV2 or PCV3, and one PCV4-positive sample was coinfected with both PCV2 and PCV3. Similar to other PCVs, PCV4 contains two major ORFs and a stem loop (TTCAGTATTAC). Multiple sequence alignments showed that the PCV4 genome shares 25.3-73.8% nucleotide similarity with other representative circovirus genomes. Interestingly, the PCV4 Cap protein shares relatively high homology (approximately 50%) with the PCV2 Cap protein and has multiple highly homologous peptides. Multiple amino acid sequence alignments of the Cap protein revealed that PCV2 and PCV4 have multiple highly homologous antigen sites and identical receptor binding sites. Therefore, PCV2 and PCV4 may have cross-protective immunogenicity. Phylogenetic analysis showed that PCV4 is closely related to mink circovirus and bat-associated circovirus. In summary, this was the first seroprevalence and genetic investigation of PCV4 in Guangxi Province, China. The results provide insights into the epidemiology and pathogenesis of this important virus.