Porcine Circovirus (PCV) Genotype 2d-Based Virus-like Particles (VLPs) Induced Broad Cross-Neutralizing Antibodies against Diverse Genotypes and Provided Protection in Dual-Challenge Infection of a PCV2d Virus and a Type 1 Porcine Reproductive and Respiratory Syndrome Virus (PRRSV).

Seok-Jin Kang,Young-Ju Jeong,Nakhyung Lee,Su-Hwa You,Min-A Lee,Sang-Ho Cha,Hyang-Sim Lee,Hye-Jeong Lee,Sung-Min Bae,Bang-Hun Hyun

doi:10.3390/pathogens10091145

Seok-Jin Kang, Young-Ju Jeong + Show 8 more

Open Access

https://doi.org/10.3390/pathogens10091145

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Abstract

As PCV2d infection has been continuously reported in swine farms in which pigs were vaccinated with PCV2a- or 2d-based vaccines, we attempted to develop a novel vaccine using a PCV2d-based capsid to enhance its protective efficacy. In this study, recombinant virus-like particles (VLPs) of rPCV2a, rPCV2b and rPCV2d were synthesized from the capsid proteins of PCV2a, PCV2b and PCV2d field isolates, respectively. A cross-neutralization assay between the VLPs induced antisera and the field isolates demonstrated the broad cross-neutralizing activities of the rPCV2d-induced antisera. Then, the protective efficacy of rPCV2d as a vaccine candidate was investigated in commercial pigs by rPCV2d vaccination and a single- or dual-challenge infection using a PCV2d strain and a type 1 PRRSV strain. High levels of anti-PCV2d IgG and neutralizing antibodies were induced 3 weeks after vaccination. After the challenge infection, the average ADWG values of the vaccinated group were higher than those of the unvaccinated group. None or a significantly low amount of (p < 0.05) reduced PCV2 genomic DNA was found in the blood, saliva and tissues of the vaccinated pigs, when compared to the unvaccinated group. Moreover, macroscopic and microscopic lesions in the tissues were significantly (p < 0.05) reduced in the vaccinated groups. This study therefore suggests that rPCV2d may be highly useful for the control of diverse field genotypes.

Highlights

Porcine circovirus type 2 (PCV2) is the main etiologic agent for a multifactorial clinical disease, causing major economic losses in the swine industry
PCV2 field strains of QIA215 (PCV2a)-ORF2, PCV2b-ORF2 and PCV2d-ORF2 proteins expressed in insect cells were self-assembled to form virus-like particles (VLPs), and the purified PCV2-ORF2 protein was analyzed by TEM to verify the proper assembly of PCV2a-VLPs (Figure 1b), PCV2b-VLPs (Figure 1c) and PCV2d-VLPs (Figure 1d)
Despite extensive nationwide PCV2 vaccination, PCV2 has been actively circulating in swine farms, leading to continuous economic loss by inducing PCVAD in the field

Summary

Introduction

Porcine circovirus type 2 (PCV2) is the main etiologic agent for a multifactorial clinical disease (porcine circovirus-associated disease, PCVAD), causing major economic losses in the swine industry. The residual viremia and viral load in the tissues of vaccinated pigs as a result of partial protection due to a low vaccine efficacy can cause serious economic losses in the swine industry through a reduced average daily weight gain and delayed shipments [14]. Taken together, this evidence suggests that the current PCV2a-based vaccines may have to be replaced in accordance with the genetic evolution of PCV2 field isolates

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