Genotypic Change and Phylogenetic Analysis of Porcine Circovirus Type 2 in Taiwanese Pig Herds

Abstract

ABSTRACT. Porcine circovirus type 2 (PCV2) is the primary causative agent of postweaning multisystemic wasting syndrome. Two major PCV2 genotypes, PCV2a and PCV2b, have been identified. To explore the prevalence of different subgroups of PCV2 in Taiwan Porcine circovirus type 2 (PCV2) is the primary causative agent of porcine circovirus-associated diseases (PCVADs) in pigs and causes significant economic losses in most pig-producing countries [27]. PCVADs can be subclinical or can include 1 or more clinical manifestations such as multisystemic disease with weight loss, respiratory signs, enteric signs, porcine dermatitis and nephropathy syndrome, and reproductive problems individually or in combination in pigs raised on farms or in other groups of pigs [27]. PCVADs are multifactorial syndromes, and factors that are currently thought to influence the outcome of PCV2 infection include the viral strain, the host, coinfections, and immune modulation [27].PCV2 is a small, non-enveloped, circular, single-stranded DNA virus containing a circular genome of 1766-1768 nucleotides [17,34]. PCV2 is a member of the genus Circovirus of the family Circoviridae [27]. Another member of this genus includes PCV1, which does not produce disease in pigs [35]. The PCV2 genome contains three open reading frames (ORFs). ORF1 encodes two replicase proteins, Rep and Rep' [4]. The viral capsid protein is encoded by ORF2 [25], which is involved in the host immune response [24]. The third ORF, ORF3, is in a different reading frame embedded within ORF1 and encodes a protein associated with apoptosis [22].PCV2 viruses are further classified into three genotypes (2a, 2b, and 2c) that differ with respect to the ORF2 sequence [9,26]. The signature motif (amino acid positions 86-89) of ORF2 can be used to distinguish PCV2a and 2b, which contain the TNKI and SNPR (L) motifs, respectively [6]. The PCV2c genotype has only been found in Denmark to date [31]. In recent years, several reports have suggested that PCV2b is the predominant genotype in many countries worldwide, including Brazil [8,11], Canada [14,15] [16,32]. In Taiwan, the first PCV2 outbreak was confirmed in 2001 [3], and a high prevalence of PCV2 infection was noted thereafter. Up to 92% of pig herds and 68.8% of weaned pigs were infected by PCV2 in Taiwan [7]; however, the genotype prevalence of PCV2 in Taiwan is not currently known. The aim of the present study was to investigate the prevalence of the PCV2 genotype in Taiwan in the last decade. MATERIALS AND METHODS Specimen collection and histopathological examination:Clinical samples (lungs, lymph nodes, spleen, brain and serum) were collected from 785 pigs from 186 herds in central and southern Taiwan during 2002-2011. These samples were mainly acquired from weaning and growing pigs with

Prevalence of Porcine Circovirus Type 2 in Naturally Infected Pigs in Abeokuta, Nigeria

“…The higher prevalence of PCV2b than PCV2a recorded could be due to a genotypic switch from PCV2a to PCV2b overtime. This is supported by other published reports [9,10,13,30]. The concurrent infection of PCV2a and PCV2b…”

Phylogeographic and genetic characterization of porcine circovirus type 2 in Taiwan from 2001–2017

“…The genotypic shift was observed in Taiwan too. PCV2b was the predominant genotype before 2007, but it was replaced by PCV2d-2 in 2010 in the swine farms of Taiwan 25 , and the latter continues to dominate. Indeed, the genotypic shift was observed in previous studies.…”

“…Therefore, the phylogenetic analysis based on the ORF2 of PCV2 is believed to be representative of a complete genome analysis 8,15 . Two genotypes, PCV2b-1C and the novel PCV2b, which were previously considered newly emerged genotypes of PCV2 in Taiwan 25,26 , were redefined in this study as PCV2d-1 or PCV2d-2 through phylogenetic analysis of ORF2 (Fig. 4).…”

“…The entire ORF2 gene of PCV2 was PCR amplified by as described by Takahagi et al . 49 , after which the DNA fragments were purified (Geneaid Biotech, Ltd, Taipei, Taiwan) and the target nucleotide sequences were determined from both orientations using an auto sequencer (ABI 3730XL, Foster City, CA, U.S.A.) 25 .…”

“…Thus, it appears that PCV2 still plays an important role in the pig industry in Taiwan. Although newly emerging strains and global genotype shifts have been continually reported, little is known regarding the genetic diversity of PCV2 in Taiwan 25,26 . To better understand the evolutionary history of PCV2 in Taiwan, in this study, we conducted a comprehensive phylodynamic and phylogeographic analysis based on the complete ORF2 gene sequences from Taiwanese PCV2 strains.

Figure 1PCV2 positivity rate in swine samples deposited at the ADDC of NPUST in Taiwan from July 2014 to December 2016.

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