Abstract
Porcine Circovirus 2 (PCV2) is a crucial swine pathogen and considered a primary causative agent of porcine circovirus-associated diseases (PCVADs), posing a serious economic threat to the swine industry across globe. The world’s biggest agricultural conglomerates have teamed up to create giant commercial pig farms across Shanghai due to the proximity of this region to more affluent lean-pork markets. Since its discovery, PCV2 has displayed extraordinary genetic diversity, and its genome is swiftly evolving through a series of mutations and recombinations. However, limited information on epidemiology, molecular characteristics, vaccine cross-protection, and the co-infection rate of PCV2 with other lethal swine diseases can adversely impact the pig production in the region. To investigate the molecular epidemic characteristics and genetic evolution of PCV2, pigs with doubtful symptoms of PCVADs were sampled from various commercial pig farms with a history of PWMS and/or PDNS across Shanghai from 2014 to 2018. Our results revealed the coexistence of multiple PCV2 genotypes (PCV2b, PCV2e, and PCV2d) among Shanghai pig herds and dominance of PCV2d among them. We also found critical amino acid substitutions in epitope regions of important capsid proteins in PCV2 isolates involved in viral replication and host immune escape. Spotted mutations may favor the prevalence and survival of various PCV2 genotypes despite availability of commercial vaccines. This study also provides insight into the co-infection status of PCV2 with major lethal swine viral diseases such as PPV and PPRSV. Collectively, these investigations will contribute to understanding the molecular epidemiology and evolution of PCV2 across the region.
Highlights
Porcine circoviruses (PCVs) are one of the smallest identified animal viruses
Porcine Circovirus type 2 (PCV2) positive samples were screened for co-infection status with PPV and porcine reproductive and respiratory syndrome virus (PRRSV) individually through RT-PCR (PCR data not shown) using specific primers (Table 1)
The majority of the PCV2 positive samples were found to be co-infected with PPV at farm (12/13; 92.30%) and sample levels (108/115; 93.91%), whereas co-infection of PCV2 with PRRSV was found to be 46.15% (6/13) and
Summary
Porcine circoviruses (PCVs) are one of the smallest identified animal viruses. They are circular, non-enveloped, single-stranded DNA viruses which belong to the Circovirus genus of the Circoviridae family [1]. Porcine Circovirus type 1 (PCV1), with a genome of 1759 nucleotides, was first detected as a contaminant from the porcine kidney cell line and is classified as non-pathogenic [2]. Porcine Circovirus type 2 (PCV2), with 1767–1768 nucleotides, was initially isolated in Canada in 1991 [3,4,5,6,7] and is considered a primary causative agent of porcine circovirus associated diseases (PCVADs), mainly postweaning multisystemic wasting syndrome, respiratory distress, acute pulmonary edema, reduced growth performance, porcine dermatitis and nephropathy syndrome, and reproductive failures, and is a serious economic threat for the pig industry and wild boar population across the globe [8,9,10]. The PCV2 genome comprises three open reading frames (ORFs). ORF-1 (rep gene) is located on the virus plus-strand and encodes two replicase proteins (Rep and Rep0 )
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