Porcine Circovirus Type 2 (PCV2) Vaccines in the Context of Current Molecular Epidemiology

Abstract

Porcine circovirus type 2 (PCV2) is an economically important swine pathogen and, although small, it has the highest evolution rate among DNA viruses. Since the discovery of PCV2 in the late 1990s, this minimalistic virus with a 1.7 kb single-stranded DNA genome and two indispensable genes has become one of the most important porcine pathogens, and presently is subjected to the highest volume of prophylactic intervention in the form of vaccines in global swine production. PCV2 can currently be divided into five different genotypes, PCV2a through PCV2e. It is well documented that PCV2 continues to evolve, which is reflected by changes in the prevalence of genotypes. During 2006, commercial vaccines for PCV2 were introduced on a large scale in a pig population mainly infected with PCV2b. Since 2012, the PCV2d genotype has essentially replaced the previously predominant PCV2b genotype in North America and similar trends are also documented in other geographic regions such as China and South Korea. This is the second major PCV2 genotype shift since the discovery of the virus. The potential increase in virulence of the emergent PCV2 genotype and the efficacy of the current vaccines derived from PCV2a genotype against the PCV2d genotype viruses has received considerable attention. This review attempts to synthesize the understanding of PCV2 biology, experimental studies on the antigenic variability, and molecular epidemiological analysis of the evolution of PCV2 genotypes.

Molecular epidemiology and genetic variation analyses of porcine circovirus type 2 isolated from Yunnan Province in China from 2016-2019

“…Since its identification in the 1970s, PCV2 has become prevalent globally. PCV2 infection normally causes immunosuppression and reduced immunity by damaging the immune system, which leads to coinfections with other pathogens, such as Porcine Reproductive and Respiratory Syndrome Virus (PRRSV), CSFV and Porcine Pseudorabies Virus (PRV), usually resulting in worse conditions, making the requirements for prevention and control more serious [3]. PCV2 infection has caused huge economic losses in pig production in China and worldwide and is recognized as one of the most important pig diseases.…”

“…The Cap protein is the only structural protein of PCV2 virus that contains immunologically important epitopes associated with virus neutralization. Therefore, the ORF2 and Cap proteins are commonly used for PCV2 phylogeny, epidemiology, and genetic diversity analyses [3]. PCV2 may evade the immune response in the form of mutations because of the immune pressure due to vaccination and may affect the antigenicity and immunogenicity of the Cap protein.…”

Structural characterization of the PCV2d genotype at 3.3 Å resolution reveals differences to PCV2a and PCV2b genotypes, a tetranucleotide, and an N-terminus near the icosahedral 3-fold axes

“…Both PCV2b and d exhibit high sequence variability (Fig 6B and 6D). The increased variability in the PCV2 genotypes may be a result of the selective pressure induced by the vaccination program in 2006 (46). The number of CP sequence entries into GenBank was dominated by PCV2a prior to the introduction of the program but was quickly shadowed by PCV2b entries.…”

Vimentin modulates infectious porcine circovirus type 2 in PK-15 cells

“…PCV2, the pathogen that causes PMWS, is an economically important swine pathogen (Darwich and Mateu, 2012;Jiang et al, 2017;Karuppannan and Opriessnig, 2017). However, the pathogenesis of PCV2 is not fully understood.…”