Genome sequence analysis of 10 Dutch porcine circovirus type 2 (PCV-2) isolates from a PMWS case-control study

Discriminating the eight genotypes of the porcine circovirus type 2 with TaqMan-based real-time PCR

Background

The porcine circovirus type 2 (PCV2) is divided into eight genotypes including the previously described genotypes PCV2a to PCV2f and the two new genotypes PCV2g and PCV2h. PCV2 genotyping has become an important task in molecular epidemiology and to advance research on the prophylaxis and pathogenesis of PCV2 associated diseases. Standard genotyping of PCV2 is based on the sequencing of the viral genome or at least of the open reading frame 2. Although, the circovirus genome is small, classical sequencing is time consuming, expensive, less sensitive and less compatible with mass testing compared with modern real-time PCR assays. Here we report about a new PCV2 genotyping method using qPCR.

Methods

Based on the analysis of several hundred PCV2 full genome sequences, we identified PCV2 genotype specific sequences or single-nucleotide polymorphisms. We designed six TaqMan PCR assays that are specific for single genotypes PCV2a to PCV2f and two qPCRs targeting two genotypes simultaneously (PCV2g/PCV2d and PCV2h/PCV2c). To improve specific binding of oligonucleotide primers and TaqMan probes, we used locked nucleic acid technology. We evaluated amplification efficiency, diagnostic sensitivity and tested assay specificity for the respective genotypes.

Results

All eight PCV2 genotype specific qPCRs demonstrated appropriate amplification efficiencies between 91 and 97%. Testing samples from an epidemiological field study demonstrated a diagnostic sensitivity of the respective genotype specific qPCR that was comparable to a highly sensitive pan-PCV2 qPCR system. Genotype specificity of most qPCRs was excellent. Limited unspecific signals were obtained when a high viral load of PCV2b was tested with qPCRs targeting PCV2d or PCV2g. The same was true for the PCV2a specific qPCR when high copy numbers of PCV2d were tested. The qPCR targeting PCV2h/PCV2c showed some minor cross-reaction with PCV2d, PCV2f and PCV2g.

Conclusion

Genotyping of PCV2 is important for routine diagnosis as well as for epidemiological studies. The introduced genotyping qPCR system is ideal for mass testing and should be a valuable complement to PCV2 sequencing, especially in the case of simultaneous infections with multiple PCV2 genotypes, subclinically infected animals or research studies that require large sample numbers.

Analysis of genetic variation of porcine circovirus type 2 within pig populations in central China

In order to investigate the genetic diversity of porcine circovirus type 2 (PCV2), 284 clinical tissue samples were collected from different pig farms in central China from 2015 to 2017. A total of 162 tissue samples (162/284, 57.04%) were positive for PCV2 by PCR, and subsequently, the complete genome of 36 of these PCV2 samples was cloned and sequenced. The sequencing results showed that 37 complete PCV2 sequences were obtained from 36 PCV2-positive clinical samples. These PCV2 strains were relatively conserved and extremely homologous to the representative classical PCV2 strains. Of these, 20 PCV2 strains belonged to genotype PCV2d, 14 belonged to PCV2b, and three others belonged to PCV2a. Coinfection with PCV2b and PCV2d was identified in one sample (DF-2). These results show that PCV2d may be gradually replacing PCV2b as the predominant PCV2 genotype in central China, and that other genotypes also exist in individual regions. The results of this study will aid in our understanding of the molecular epidemiology of PCV2.

Current Knowledge on Porcine circovirus 3 (PCV-3): A Novel Virus With a Yet Unknown Impact on the Swine Industry

Porcine circovirus 3 (PCV-3) is a recently described virus belonging to the family Circoviridae. It represents the third member of genus Circovirus able to infect swine, together with PCV-1, considered non-pathogenic, and PCV-2, one of the most economically relevant viruses for the swine worldwide industry. PCV-3 was originally found by metagenomics analyses in 2015 in tissues of pigs suffering from porcine dermatitis and nephropathy syndrome, reproductive failure, myocarditis and multisystemic inflammation. The lack of other common pathogens as potential infectious agents of these conditions prompted the suspicion that PCV-3 might etiologically be involved in disease occurrence. Subsequently, viral genome was detected in apparently healthy pigs, and retrospective studies indicated that PCV-3 was already present in pigs by early 1990s. In fact, current evidence suggests that PCV-3 is a rather widespread virus worldwide. Recently, the virus DNA has also been found in wild boar, expanding the scope of infection susceptibility among the Suidae family; also, the potential reservoir role of this species for the domestic pig has been proposed. Phylogenetic studies with available PCV-3 partial and complete sequences from around the world have revealed high nucleotide identity (>96%), although two main groups and several subclusters have been described as well. Moreover, it has been proposed the existence of a most common ancestor dated around 50 years ago. Taking into account the economic importance and the well-known effects of PCV-2 on the swine industry, a new member of the same family like PCV-3 should not be neglected. Studies on epidemiology, pathogenesis, immunity and diagnosis are guaranteed in the next few years. Therefore, the present review will update the current knowledge and future trends of research on PCV-3.

Multiplex real-time polymerase chain reaction for the differential detection of porcine circovirus 2 and 3

A multiplex quantitative real-time polymerase chain reaction (mqPCR) assay was developed for the rapid and differential detection of porcine circovirus 2 (PCV2) and PCV3. Each of the capsid genes of PCV2 and PCV3 were amplified using specific primers and probe sets, while no other porcine pathogen genes were detected. Limit of detection of the assay was below 50 copies of the target genes of PCV2 and PCV3, and was comparable to that of previously described methods The assay showed high repeatability and reproducibility, with coefficients of intra-assay and inter-assay variation of less than 4.0%. Clinical evaluation using tissue samples from a domestic pig farm showed that PCV2 and PCV3 co-circulated at the farm. Moreover, singular infection rates of PCV2 or PCV3 were 21.7% (10/46) or 6.5% (3/46), respectively, while the co-infection rate of PCV3 with PCV2 was 28.3% (13/46). PCV3 DNA was detected by the mqPCR in respiratory diseased piglet tissue samples and aborted fetal tissue samples, suggesting that PCV3 infection is associated with porcine respiratory disease and reproductive failure in the pig farm. This mqPCR method is a rapid and reliable differential diagnostic tool for the monitoring and surveillance of PCV2 and PCV3 in the field.

A Novel Porcine Circovirus Distantly Related to Known Circoviruses Is Associated with Porcine Dermatitis and Nephropathy Syndrome and Reproductive Failure

Porcine circovirus-associated disease (PCVAD) is clinically manifested by postweaning multisystemic wasting syndrome (PMWS), respiratory and enteric disease, reproductive failure, and porcine dermatitis and nephropathy syndrome (PDNS). Porcine circovirus 2 (PCV2) is an essential component of PCVAD, although an etiologic role in PDNS is not well established. Here, a novel circovirus, designated porcine circovirus 3 (PCV3), was identified in sows that died acutely with PDNS-like clinical signs. The capsid and replicase proteins of PCV3 are only 37% and 55% identical to PCV2 and bat circoviruses, respectively. Aborted fetuses from sows with PDNS contained high levels of PCV3 (7.57 × 10⁷ genome copies/ml), and no other viruses were detected by PCR and metagenomic sequencing. Immunohistochemistry (IHC) analysis of sow tissue samples identified PCV3 antigen in skin, kidney, lung, and lymph node samples localized in typical PDNS lesions, including necrotizing vasculitis, glomerulonephritis, granulomatous lymphadenitis, and bronchointerstitial pneumonia. Further study of archived PDNS tissue samples that were negative for PCV2 by IHC analysis identified 45 of 48 that were PCV3 positive by quantitative PCR (qPCR), with 60% of a subset also testing positive for PCV3 by IHC analysis. Analysis by qPCR of 271 porcine respiratory disease diagnostic submission samples identified 34 PCV3-positive cases (12.5%), and enzyme-linked immunosorbent assay detection of anti-PCV3 capsid antibodies in serum samples found that 46 (55%) of 83 samples tested were positive. These results suggest that PCV3 commonly circulates within U.S. swine and may play an etiologic role in reproductive failure and PDNS. Because of the high economic impact of PCV2, this novel circovirus warrants further studies to elucidate its significance and role in PCVAD.

IMPORTANCE

While porcine circovirus 2 (PCV2) was first identified in sporadic cases of postweaning multisystemic wasting syndrome in Canada in the early 1990s, an epidemic of severe systemic disease due to PCV2 spread worldwide in the ensuing decade. Despite being effectively controlled by commercial vaccines, PCV2 remains one of the most economically significant viruses of swine. Here, a novel porcine circovirus (PCV3) that is distantly related to known circoviruses was identified in sows with porcine dermatitis and nephropathy syndrome (PDNS) and reproductive failure. PCV2, which has previously been associated with these clinical presentations, was not identified. High levels of PCV3 nucleic acid were observed in aborted fetuses by quantitative PCR, and PCV3 antigen was localized in histologic lesions typical of PDNS in sows by immunohistochemistry (IHC) analysis. PCV3 was also identified in archival PDNS diagnostic samples that previously tested negative for PCV2 by IHC analysis. The emergence of PCV3 warrants further investigation.

Molecular detection and genome characterization of porcine circovirus type 2 in rats captured on commercial swine farms

Porcine circovirus type 2 (PCV2) is considered the major etiological pathogen of porcine circovirus-associated diseases (PCVADs) in pigs. Recently, PCV2 was also found in non-porcine animals such as cattle, rats, and mice. However, there was no record of PCV2 in rats in China. The goal of this study was to investigate whether PCV2 was present in rats (Rattus norvegicus, RN) on three swine farms, using molecular tools. PCR results showed that 30 of 95 (31.6 %) rat samples were positive for PCV2. Moreover, further genotype analysis suggested that 10 of 30 (33.3 %) were positive for PCV2a, 19 of 30 (63.3 %) were positive for PCV2b, and only one sample (1/30, 3.33 %) was co-infected by PCV2a and PCV2b. To determine the possible origin of PCV2, 60 serum samples were also collected from weaned pigs on those swine farms, and 23 out of 60 samples were positive for PCV2. In addition, two distinct RN-origin and two distinct porcine-origin PCV2 full-length nucleotide sequences were obtained from the farms. Sequence and phylogenetic analysis indicated that they had the highest nucleotide similarity and closest genetic relationships to each other. In this study, we report the infection and genome characterization of PCV2 in rats and compare RN-origin and porcine-origin PCV2 sequences obtained from the same pig farm, revealing possible cross-species transmission of PCV2.

Oral application of freeze-dried yeast particles expressing the PCV2b Cap protein on their surface induce protection to subsequent PCV2b challenge in vivo

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PCV2 is the underlying cause for an economically devastating disease of pigs.

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Vaccine construct was PCV2b Cap protein expressed on the surface of yeast.

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Oral vaccination of freeze-dried yeast-Cap did not induce negative side effects.

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Application protected pigs from subsequent PCV2b challenge.

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Vaccination reduced pro-inflammatory but increased antiviral cytokine expression.

Porcine circovirus type 2 (PCV2) is now endemic in every major pig producing country, causing PCV-associated disease (PCVAD), linked with large scale economic losses. Current vaccination strategies are based on the capsid protein of the virus and are reasonably successful in preventing PCVAD but fail to induce sterile immunity. Additionally, vaccinating whole herds is expensive and time consuming. In the present study a “proof of concept” vaccine trial was employed to test the effectiveness of powdered freeze-dried recombinant Saccharomyces cerevisiae yeast stably expressing the capsid protein of PCV2b on its surface as an orally applied vaccine. PCV2-free pigs were given 3 doses of vaccine or left un-vaccinated before challenge with a defined PCV2b strain. Rectal temperatures were measured and serum and faeces samples were collected weekly. At the end of the study, pigs were euthanized, tissue samples taken and tested for PCV2b load by qPCR and immunohistochemistry. The peak of viraemia in sera and faeces of unvaccinated pigs was higher than that of vaccinated pigs. Additionally more sIgA was found in faeces of vaccinated pigs than unvaccinated. Vaccination was associated with lower serum concentrations of TNFα and IL-1β but higher concentrations of IFNα and IFNγ in comparison to the unvaccinated animals. At the end of the trial, a higher viral load was found in several lymphatic tissues and the ileum of unvaccinated pigs in comparison to vaccinated pigs. The difference between groups was especially apparent in the ileum. The results presented here demonstrate a possible use for recombinant S. cerevisiae expressing viral proteins as an oral vaccine against PCV2. A powdered freeze-dried recombinant S. cerevisiae used as an oral vaccine could be mixed with feed and may offer a cheap and less labour intensive alternative to inoculation with the additional advantage that no cooling chain would be required for vaccine transport and storage.

Genetic characterization of porcine circovirus type 2 in the Korean wild boar population

The porcine circovirus type 2 (PCV2) has reached very high levels in the pig population in South Korea and throughout the world since it was first described in the late 1990s. In this study, we found that the prevalence of PCV2 in the Korean wild boar population was 4.98% (91/1825). Interestingly, 19 PCV2 ORF2 sequences that could be completely sequenced showed that they belonged only to genotype PCV2b, subgroup 1A/B (n=16) and 1C (n=3). We suggest that sites potentially under positive selection are responsible for the antigenicity changes and phenotypic switch patterns in the capsid gene of 55 PCV2s from Korean domestic pigs, but the sites potentially under positive selection in the 19 PCV2 ORF2 genes from Korean wild boar are not responsible for antigenicity.

Dual heterologous porcine circovirus genogroup 2a/2b infection induces severe disease in germ-free pigs

Our primary objectives were to determine: the relative virulence of porcine circovirus (PCV) 2a and PCV2b, if heterologous infection induces severe illness, and the relative concentration of PCV2a and PCV2b in tissues of heterologously infected pigs. In experiment 1, 18 germ-free piglets served as controls or were infected with PCV2a or PCV2b. Half were immune stimulated with keyhole limpet hemocyanin (KLH) emulsified in incomplete Freund's adjuvant (2aKLH, 2bKLH). No piglets demonstrated severe illness. Lesion severity did not differ, but PCV2 capsid staining was more intense in 2a- than 2b-infected pigs (P<.05). In experiment 2, 20 germ-free piglets were dual inoculated 7 days apart with PCV2a and PCV2b (2a2b, 2b2a), PCV2b twice (2b2b), or PCV2a (2a2a) twice. Five of 9 heterologous-infected pigs developed severe illness. All heterologously infected pigs demonstrated ascites or edema, and 8/9 developed thymic atrophy. By contrast, 1 of 5 2b2b-infected pigs developed bronchopneumonia and pleural effusion. No 2a2a-infected pig developed illness. Gross lesions were more severe in heterologously infected pigs than in 2b2b pigs (P<.05), and were more severe in 2b2b than 2a2a pigs (P<.05). PCV2 capsid staining intensity did not differ by group. In heterologously infected pigs, higher levels of PCV2 DNA reflective of the first inoculum compared to the second were found in mesenteric lymph node (P=.04), spleen (P=.004) and liver (P=.04). These results indicate that dual heterologous PCV2a/2b inoculation 7 days apart may induce severe clinical illness, but PCV2a and PCV2b when administered singularly or in combination with KLH appear to be of equivalent virulence.

Porcine circovirus type 2 and porcine circovirus-associated disease

Porcine circovirus type 2 (PCV2) belongs to the viral family Circoviridae and to the genus Circovirus. Circoviruses are small, single-stranded nonenveloped DNA viruses that have an unsegmented circular genome. PCV2 is the primary causative agent of several syndromes collectively known as porcine circovirus-associated disease (PCVAD). Many of the syndromes associated with PCVAD are a result of coinfection with PCV2 virus and other agents such as Mycoplasma and porcine reproductive and respiratory syndrome virus. PCV2 infection is present in every major swine-producing country in the world, and the number of identified cases of PCVAD is rapidly increasing. In the United States, the disease has cost producers an average of 3-4 dollars per pig with peak losses ranging up to 20 dollars per pig. The importance of this disease has stimulated investigations aimed at identifying risk factors associated with infection and minimizing these risks through modified management practices and development of vaccination strategies. This paper provides an overview of current knowledge relating to PCV2 and PCVAD with an emphasis on information relevant to the swine veterinarian.

Antigenic differences among porcine circovirus type 2 strains, as demonstrated by the use of monoclonal antibodies

This study examined whether antigenic differences among porcine circovirus type 2 (PCV-2) strains could be detected using monoclonal antibodies (mAbs). A subtractive immunization protocol was used for the genotype 2 post-weaning multisystemic wasting syndrome (PMWS)-associated PCV-2 strain Stoon-1,010. Sixteen stable hybridomas that produced mAbs with an immunoperoxidase monolayer assay (IPMA) titre of 1,000 or more to Stoon-1,010 were obtained. Staining of recombinant PCV-2 virus-like particles demonstrated that all mAbs were directed against the PCV-2 capsid protein. Cross-reactivity of mAbs was tested by IPMA and neutralization assay for genotype 1 strains 48,285, 1,206, VC2,002 and 1,147, and genotype 2 strains 1,121 and 1,103. Eleven mAbs (9C3, 16G12, 21C12, 38C1, 43E10, 55B1, 63H3, 70A7, 94H8, 103H7 and 114C8) recognized all strains in the IPMA and demonstrated neutralization of Stoon-1,010, 48,285, 1,206 and 1,103, but not VC2,002, 1,147 and 1,121. mAbs 31D5, 48B5, 59C6 and 108E8 did not react with genotype 1 strains or had a reduced affinity compared with genotype 2 strains in the IPMA and neutralization assay. mAb 13H4 reacted in the IPMA with PMWS-associated strains Stoon-1,010, 48,285, 1,206 and VC2,002, and the porcine dermatitis and nephropathy syndrome-associated strain 1,147, but not with reproductive failure-associated strains 1,121 and 1,103. mAb 13H4 did not neutralize any of the tested strains. It was concluded that, despite the high amino acid identity of the capsid protein (>or=91 %), antigenic differences at the capsid protein level are present among PCV-2 strains with a different genetic and clinical background.

A survey on porcine circovirus type 2 infection and phylogenetic analysis of its ORF2 gene in Hangzhou, Zhejiang Province, China

Porcine circovirus type 2 (PCV2) is closely related to the postweaning multisystemic wasting syndrome (PMWS). In this study, the pig serum and tissue samples collected from different regions of Hangzhou District in Zhejiang Province of China between 2003 and 2005 were analyzed by enzyme-linked immunosorbent assay (ELISA) for PCV2 antibody and by polymerase chain reaction (PCR) for ORF2 gene. The results show that out of 1250 randomly collected serum samples, 500 sera (40%) were seropositive for PCV2. PCR results demonstrate that Hangzhou PCV2 with more than 50% Chinese PCV2 strains and French PCV2 formed Cluster A. Only one PCV2 from Hangzhou belonged to Cluster B with some other Chinese PCV2 and Netherlands's isolates. Cluster C consisted of PCV2 isolates from China, US, Canada, UK and Germany. The results indicate that the PCV2 infection was widespread in Hangzhou.

Porcine circovirus type 2 associated disease: update on current terminology, clinical manifestations, pathogenesis, diagnosis, and intervention strategies

Porcine circovirus type 2 (PCV2)-associated disease (PCVAD) continues to be an important differential diagnosis on pig farms in the United States and worldwide. Case trend analyses indicate that the incidence of PCVAD is on the rise in the United States. Accurate diagnosis is important in order to implement appropriate intervention strategies. PCVAD can manifest as a systemic disease, as part of the respiratory disease complex, as an enteric disease, as porcine dermatitis and nephropathy syndrome, or as reproductive problems. PCVAD may be only a sporadic individual animal diagnosis; however, PCVAD may also manifest as a severe herd problem accelerated and enhanced by concurrent virus or bacterial infections. This article is intended to discuss the most common disease manifestations, pathogenesis, diagnostic approaches, and intervention strategies associated with PCVAD in North America.

Evidence for recombination between PCV2a and PCV2b in the field

Genomic sequence analysis demonstrates that porcine circovirus type 2 (PCV2) isolates are divided into distinct genotypes. Historically, swine herds in the U.S. have been infected with the PCV2a genotype. In 2005, PCV2b was identified in North America and with it increased reports of porcine circovirus disease (PCVD). A differential PCR technique incorporating PCV2 genotype-specific primers was used in the clinical diagnosis of PCVD. A set of 97 diagnostic submissions showed that both PCV2a and PCV2b were present in 25% of clinical samples. The construction of phylogenetic trees using whole genome sequences from diagnostic submissions showed that one isolate, 0737A, was only loosely associated with other PCV2b isolates. Analysis of the variable sites between representative PCV2a and PCV2b DNA sequences and the 0737A sequence, showed that 0737A was a mosaic sequence, with the ORF1 region from PCV2a and ORF2 from PCV2b. This study demonstrates that pigs can be naturally infected with multiple PCV2 genotypes and that PCV2a/PCV2b recombination events occur in the field.

Ontogeny of systemic cellular immunity in the neonatal pig: Correlation with the development of post-weaning multisystemic wasting syndrome

The aetiology of porcine post-weaning multisystemic wasting syndrome (PMWS) is poorly understood. Porcine circovirus type 2 (PCV-2) is an essential component of the experimental disease model for PMWS: however, evidence from experimental and field studies indicates that additional factors play a critical role in the aetiopathogenesis of PMWS. Current candidates include (1) immune stimulation (for example, via co-infection or vaccination), and (2) a novel infectious agent. A prospective, longitudinal case-control study was designed to investigate molecular triggers in leucocytes of neonatal piglets that may predispose to the development of PMWS. Blood samples were collected weekly from pigs (n=125) within five farms, from 1 week to 8 weeks of age: that is, before the appearance of clinical signs. Four colour flow cytometry was used to investigate changes in subsets of peripheral blood mononuclear cells, using monoclonal antibodies against the following cell associated markers; sIgG, CD3, MHCII dR, CD14, CD4a, CD8a, CD45RC, CD25, SWC3a, SWC8, CD163 and CD45. Sampling and laboratory analysis was supported by monitoring of clinical signs from 1 week to 20 weeks of age, or until disease supervened. At the conclusion of the study, 68 pigs (54%) were classified in Group 1 (no signs of clinical disease), 34 pigs (27%) in Group 2 (signs of clinical disease but not characteristic of PMWS), 17 pigs (14%) in Group 3 (suspect PMWS case) and 5 pigs (4%) in Group 4 (PMWS case). A single case of Porcine Dermatitis and Nephropathy syndrome (PDNS) was also diagnosed. Significant changes with age were demonstrated in clinically normal, neonatal pigs (Group 1), including an increase in B-cells and T-cells, and an increase in the proportion of total T-cells expressing MHCII. Within the T-cell subset, the proportion of CD8(+high) CD4(-) T-cells increased, in addition to the proportion of CD4(+) T-cells co-expressing CD8. Of the factors recorded, farm was found to have a highly significant effect on immune system development in the neonate. Comparison of Groups 1 and 4 cases identified significant differences between pigs which remained normal and those which subsequently developed PMWS. Pigs which went on to develop PMWS had a greater proportion of T-cells expressing MHCII in early life, higher mean intensity of expression of MHCII on T-cells, higher mean intensity of expression of MHCII on B cells and higher expression of CD25 on CD45RC(-) T-cells. These findings suggest that lymphocyte activation may be a key early event in the aetiology of PMWS.

A proposal on porcine circovirus type 2 (PCV2) genotype definition and their relation with postweaning multisystemic wasting syndrome (PMWS) occurrence

Porcine circovirus type 2 (PCV2) is the essential infectious agent of postweaning multisystemic wasting syndrome (PMWS). Despite first sequencing studies did not find any association between PCV2 sequences and PMWS occurrence, recent works have suggested the opposite. In the present study, 87 open reading frame 2 (ORF2) sequences obtained from pigs with different clinical conditions and coming from farms with different PMWS status were analyzed. Results further confirmed the existence of two genogroups and the definition of two PCV2 genotypes (1 and 2) is proposed. All sequences included in genotype 1 came from pigs from PMWS affected farms, while all sequences obtained from non-PMWS affected farms corresponded to genotype 2. Moreover, infection of single pigs from PMWS affected farms harbouring both genotypes is described. Present results suggest that PCV2 genotype 1 may potentially be more pathogenic than PCV2 genotype 2.

Genetic characterization of porcine circovirus type 2 in Republic of Korea

Porcine circovirus type 2 (PCV2) is a major causative agent of postweaning multisystemic wasting syndrome (PMWS). Sequence and phylogenetic analyses based on the ORF2 capsid protein gene fragment showed that field isolate in Republic of Korea (ROK), PCV2 YJK 0703, was closely related with the PCV2 Fh18 isolate. PCV2 YJK 0703 was genetically distinct and not related to previously reported ROK isolates. Therefore, genotypic variation exists among prevailing PCV2 in ROK. This result suggests that several PCV2 genotypes exist in Korean pig farms.

Phylogenetic characterization of porcine circovirus type 2 in PMWS and PDNS Korean pigs between 1999 and 2006

Porcine circovirus type 2 (PCV2) has been associated with several disease outcomes in swine, primarily postweaning multisystemic wasting syndrome (PMWS) and porcine dermatitis nephropathy syndrome (PDNS). Over an 8-year period (1999-2006), we detected 36 PCV2 strains from PMWS and PDNS cases. Complete genes of the detected PCV2 strains were sequenced and analyzed. The sequences encoding a putative capsid protein, ORF2, of 233 PCV2 strains, isolated in Korea and throughout the world, could be divided into two groups (1 and 2) by phylogenetic tree analysis and multiple alignments of nucleotide sequences. Group 1 has the sequence CCCCG/TC and group 2 has the sequence AAAATC at nucleotides 262-267 of ORF2. Group 1 has PR/L and 2 has KI at amino-acid positions 88-89 of ORF2. Of the 233 PCV2 strains, 153 (65.7%) were placed in group 1 and 80 (34.4%) were in group 2 by phylogenetic characterization analysis using CLUSTER X 1.83, Puzzle 5.2, and PHYLIP 3.66 software package. Geographical analysis showed that PCV2 strains detected from the Netherlands, Thailand, and the United Kingdom were included in group 1. In contrast, PCV2 isolates from Japan, Canada, Spain, Taiwan, and South Africa belonged to group 2. Both groups were found in isolates from Korea, France, Hungary, Austria, Germany, Brazil, and the United States. Pathogenic analysis showed that PCV2 isolates from healthy pigs and from PDNS cases also fell into the two groups. PCV2 isolates from PMWS cases induced by PCV2 alone also fell into both groups.

Genetic diversity of Brazilian strains of porcine circovirus type 2 (PCV-2) revealed by analysis of the cap gene (ORF-2)

Porcine circovirus 2 (PCV-2) is associated with a broad range of syndromes. In this study, 19 of 870 samples from pigs from different Brazilian states were found to be positive for PCV-2 by polymerase chain reaction (PCR). A fragment of 700 nt of the cap gene (ORF-2) from the 19 PCV-2-positive samples were sequenced using three pairs of primers (Fa/Ra, Fb/Rb and Fc/Rc). Maximum parsimony genealogy with a heuristic algorithm using the 19 field strain studied here, 21 sequences from GenBank and PCV-1 as an out-group showed the existence of two major clusters (A and B) and the Brazilian strains segregating in both of them. PCV-2 was found in pigs with various clinical signs. No association between clusters of PCV-2 and different states or clinical signs were observed, demonstrating that the exact role of PCV-2 in porcine circovirus diseases (PCVD) in Brazil still needs to be clarified. These results contribute to the molecular characterization of PCV-2, which serve as a basis for the epimiology of PCV-2 infection.

Molecular evolution of porcine circovirus type 2 genomes: Phylogeny and clonality

Porcine circoviruses (PCVs) type 1 (PCV1) and type 2 (PCV2) show high levels of nucleotide similarity, but PCV1 is considered non-pathogenic and PCV2 has been associated with several disease outcomes in pigs, mainly postweaning multisystemic wasting syndrome (PMWS). After exploring different topologies of the origin of PCVs, it was concluded that PCV1 and PCV2 seem to have a common origin. On the other hand, PCV2 could be divided into two groups (1 and 2) and eight clusters (1A to 1C and 2A to 2E), but none of those was apparently associated with disease status or geographic area. When phylogenetic trees constructed with the whole PCV2 genome, the cap or the rep genes were compared, some incongruence was identified. The possible existence of recombination was evaluated and cluster 1B was found to have a possible recombinant origin. Selective pressure was detected in all parts of the PCV2 genome, especially in the rep gene. Finally, the cap gene was the more suitable phylogenetic and epidemiological marker for PCV2, despite the fact that the virus can undergo recombination mainly within the first part of the rep region.

Genetic and experimental comparison of porcine circovirus type 2 (PCV2) isolates from cases with and without PCV2-associated lesions provides evidence for differences in virulence

There are marked differences in the clinical expression of diseases associated with porcine circovirus type 2 (PCV2) in the field. The objective of this study was to compare the sequences and pathogenicity of PCV2 isolates from field cases with and without PCV2-associated lesions. Forty-two specific-pathogen-free (SPF) pigs were assigned randomly to three groups of 14 pigs each. At 7 weeks of age, group 1 pigs were mock-inoculated with saline, group 2 pigs were inoculated with PCV2-4838 (isolated from a pig with no evidence of PCV2-associated lymphoid lesions) and group 3 pigs were inoculated with PCV2-40895 (isolated from a pig with PCV2-associated lymphoid lesions and disease). The PCV2-4838 and PCV2-40895 isolates shared approximately 98.9 % nucleotide sequence identity across the entire genome. A total of nine amino acid changes in ORF2 and two amino acid changes in ORF1 were identified between the two isolates. PCV2-4838-inoculated pigs had significantly more genomic copy numbers of PCV2 in their sera at 7 days post-inoculation (p.i.) (P<0.0001) and significantly fewer genomic copy numbers at 14, 21 and 28 days p.i. (P<0.05) compared with pigs inoculated with the PCV2-40895 isolate. Microscopic lesions in lymphoid tissues were significantly less severe (P<0.05) and the amount of PCV2 antigen associated with these lesions was significantly lower (P<0.05) in pigs inoculated with PCV2-4838. The results of this study suggest that PCV2 isolates from the USA differ in virulence in an SPF pig model.