Abstract
Porcine circovirus type 3 (PCV3), a virus belonging to the Circoviridae family, is considered to be associated with respiratory and neurological signs, cardiac and multisystemic inflammation, reproductive failure, and porcine dermatitis and nephropathy syndrome-like disease in pigs (Sus scrofa). In this study, epidemiological and serological investigations of PCV3 in clinically healthy pigs from different regions of China were performed. Overall, 42.87% (1,101/2,568) of pigs were positive for PCV3 Cap antibody via indirect enzyme-linked immunosorbent assay, with a higher prevalence of PCV3 in multiparous sows (62.22%, 881/1,416) and fattening pigs (28.96%, 159/549) than in suckling piglets (8.96%, 32/357) and nursery pigs (11.79%, 29/246). Of the 2,568 samples, 255 were further tested for PCV3 DNA using real-time polymerase chain reaction, and 63.14% of these were positive, with nearly half having <10 virus copies. The PCV3 DNA and antibody positivity rates were high in the pig serum samples; however, the virus titers and antibody levels were both low, indicating that the humoral immune response of PCV3-infected pigs was weak or lagging, and persistent or repeated infections could occur. Additionally, the complete genomes of 23 PCV3 strains were sequenced and analyzed, which showed nucleotide identities of 98.5~100.0%, 98.6~100.0%, and 99.2~100.0% in the complete genome, open reading frame (ORF)2, and ORF1 sequences, respectively, and amino acid identities of 96.7~100.0% and 99.3~100.0% in the capsid and replicase proteins, respectively. Phylogenetic analysis based on ORF2 nucleotide sequences indicated that the PCV3 strains obtained in the present study could be classified into three sub-clades, with most strains clustered into clade 3c, indicating that PCV3c is the dominant subtype in the regions of China investigated. In general, the present study revealed a high prevalence and high genetic divergence of PCV3 among Chinese pig herds, and indicated that the potential effect of PCV3 on the pig industry may be a concern.
Highlights
Porcine circoviruses (PCVs), belonging to the genus Circovirus of the family Circoviridae, are single-stranded circular DNA viruses with a genome of nearly 2 kb [1]
The Porcine circovirus type 3 (PCV3) strains prevalent worldwide have been divided into two genotypes (PCV3a and PCV3b) based on the genetic characteristics of PCV3 complete genome, and the prevalence of PCV3a has recently increased [24]
Considering the fact that there are no available vaccines against PCV3, obtaining accurate information on the prevalence and genetic characteristics of PCV3 circulating in China will provide scientific data for developing effective measures against this infectious disease
Summary
Porcine circoviruses (PCVs), belonging to the genus Circovirus of the family Circoviridae, are single-stranded circular DNA viruses with a genome of nearly 2 kb [1]. PCV3 infection was first reported in the USA in 2016 by metagenomic sequencing of tissue samples from pigs (Sus scrofa) with porcine dermatitis and nephropathy syndrome (PDNS), reproductive failure, myocarditis, and multi-systemic inflammation [4, 5]. The Cap protein plays an important role in the antigenicity of circoviruses, including PCV2 and PCV3 [7], and PCV3 strains circulating worldwide can be divided into two subtypes (PCV3a and PCV3b) based on the amino acid sequence of the Cap protein [8,9,10]
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