Abstract
Porcine circovirus type 2 (PCV2) commercial vaccines are either inactivated PCV2 isolates or subunit vaccine based on the Cap protein of PCV2. Currently, no live-attenuated vaccines are yet available. Although the predominant circulating subtype worldwide is PCV2b, the emerging PCV2d subtype is also increasingly associated with PCV disease. In this study, piglets were inoculated with a live-attenuated chimeric PCV1-2b vaccine before challenged with PCV2b and PCV2d isolates. Thirty-two piglets were randomly divided into seven groups: negative (sham-vaccinated, sham-challenged), VAC+PCV2b (PCV1-2b vaccinated, PCV2b-challenged), VAC+PCV2d (PCV1-2b vaccinated, PCV2d-challenged), CHAL+PCV2b (sham-vaccinated, PCV2b-challenged), CHAL+PCV2d (sham-vaccinated, PCV2d-challenged), CV+PCV2b (commercial-vaccinated, PCV2b-challenged), and CV+PCV2d (commercial-vaccinated, PCV2d-challenged). The results showed that vaccinated challenged groups demonstrated high levels of anti-PCV2 antibody and reduced PCV2b and PCV2d loads both in serum and nasal swabs compared with the challenge-only groups. PCV2 DNA was detected in the superficial inguinal lymph nodes of only one pig in each of the VAC+PCV2b and VAC+PCV2d groups (group mean values, 101.81 and 101.77 genomic copies/g, respectively), which was significantly lower than those in CHAL+PCV2b and CHAL+PCV2d animals (group mean values, 1011.65 and 1010.60 genomic copies/g, respectively; P < 0.01). In addition, PCV2 DNA in each of the VAC+PCV2b and VAC+PCV2d groups was significantly lower than those in CV+PCV2b and CV+PCV2d animals (group mean values, 108.47 and 108.34 genomic copies/g, respectively; P < 0.01), indicating that the live-attenuated PCV1-2b vaccine was more effective than commercial vaccine. The live-attenuated PCV1-2b vaccine was effective in reducing PCV2b/PCV2d viremia, shedding, and tissue viral loads in vaccinated challenged pigs compared with challenge-only piglets, indicating that the PCV1-2b prototype vaccine is a good candidate for a live-attenuated vaccine against both PCV2b and PCV2d subtypes. And we first revealed that the live-attenuated PCV1-2b vaccine could protect piglets from challenge with either PCV2b or PCV2d equivalently.
Highlights
MATERIALS AND METHODSPorcine circovirus type 2 (PCV2) is the primary causative agent of global porcine circovirus disease (PCVD)
The emergence of PCV2d has been linked to PCVD outbreaks in PCV2-vaccinated herds with vaccines based on PCV2a strains (Opriessnig et al, 2013; Seo et al, 2014; Ramos et al, 2015), but one study shows that the PCV2a inactivated vaccine was effective in protecting pigs against PCV2d infection (Opriessnig et al, 2017)
We found that chimeric Porcine circovirus type 1 (PCV1)-2b can be detected in serum, and the PCV1-2b detection rate and content showed a downward trend at 28 days post-vaccination (DPV)
Summary
Porcine circovirus type 2 (PCV2) is the primary causative agent of global porcine circovirus disease (PCVD). Porcine circovirus type 1 (PCV1) was discovered as a contaminant of the porcine kidney PK-15 cell line in the mid-1970s and is non-pathogenic in pigs. These viruses share approximately 83% nucleotide sequence identity in ORF1, but only 67% identity in ORF2 (Allan and Ellis, 2000). The PCV2 genotype shifted from PCV2a toward PCV2b and was associated with an apparent increase in severity of PCVD in pig herds (Dupont et al, 2008). Several studies indicate that PCV2d is replacing PCV2a and PCV2b to become the predominant strain in pig populations (Franzo et al, 2016). Piglets were inoculated with a novel liveattenuated chimeric PCV1-2b vaccine and challenged with PCV2b or PCV2d. Statistical analysis was performed using Prism v6.0 (GraphPad Software, La Jolla, CA, United States), and expressed as mean values with standard deviations
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