Genetic variation analysis of Chinese strains of porcine circovirus type 2

Epidemiological investigation and analysis of the infection of porcine circovirus in Xinjiang

Porcine circoviruses, particularly porcine circovirus type 2 (PCV2) and porcine circovirus type 3 (PCV3), significantly impact the global pig industry due to their high prevalence and pathogenicity. Conversely, porcine circovirus type 1 (PCV1) and porcine circovirus type 4 (PCV4) currently have low positivity rates. This study aimed to characterize the distribution and epidemiology of porcine circoviruses in Xinjiang, while also analyzing the genetic diversity and evolution of PCV2 and PCV3, which pose the greatest threats to the industry. In this study, we collected blood and tissue samples from 453 deceased pigs across eight regions in Xinjiang Province from 2022 to 2024. We utilized real-time PCR to detect the presence of PCV1, PCV2, PCV3, and PCV4. The positive rates were 15%, 71%, 25%, and 17%, respectively. Genetic analysis showed 9 PCV2 sequences and 12 PCV3 sequences. The capsid protein of PCV2 showed significant variability. In contrast, the amino acid sequences of capsid in PCV3 were relatively stable. Moreover, we predicted antigenic epitopes for PCV3 capsid using IEDB and ElliPro. The findings from this study provide valuable epidemiological data on PCV coinfection in the Xinjiang region and enhance the understanding of virus diversity nationwide. This research may serve as an important reference for the development of strategies to prevent and control porcine circovirus infections.

Molecular evolution and genotype shift of Porcine circoviruses type 2 in Vietnam

Porcine Circovirus Type 2 (PCV2), a significant pathogen in the global swine industry, causes Porcine Circovirus Associated Diseases (PCVAD), contributing to substantial economic losses. This study investigates the genetic diversity and evolutionary dynamics of PCV2 in Vietnam from 2007 to 2023. We sequenced and analyzed 47 PCV2 genomes isolated from swine farms across Vietnam between 2022 and 2023, revealing predominant circulation of PCV2d (80.85%) followed by PCV2b (19.15%). Phylogenetic analysis identified PCV2 genotypes PCV2a, PCV2b, PCV2d, PCV2g, and PCV2h circulating in Vietnam, with PCV2d emerging as the most prevalent genotype. Comparison with historical data highlighted genotype shifts from PCV2b to PCV2d in 2014. Interestingly, PCV2h genotype was mainly observed between 2008 and 2012 but have not been detected since 2014. Regional analysis indicated varied PCV2 epidemiological patterns between northern and southern Vietnam. Amino acid substitutions within the capsid protein were identified, predominantly in antigenic regions critical for immune recognition. Positive selection analysis identified multiple sites under evolutionary pressure, indicating ongoing adaptation of Vietnamese PCV2 strains. These findings enhance understanding of PCV2 dynamics in Vietnam and underscore the importance of continuous surveillance and adaptive management strategies in controlling PCV2-associated diseases in swine populations.

Isolation and pathogenicity of porcine circovirus type 2 in mice from Guangxi province, China

BACKGROUND

Porcine circovirus type 2 (PCV2), a member of the genus Circovirus and family Circoviridae, is a closed, small, circular, and single-stranded DNA virus, and it is a crucial swine pathogen of porcine circovirus-associated diseases (PCVADs). PCV2 was first detected in PK-15(ATCC-CCL) cells in 1974, which has caused significant economic loss to the swine industry throughout the world. And the first case of PCV2 was reported in China in 2000. At present, PCV2d is the main genotype circulating widely in China.

METHODS

Lymph samples were obtained from piglets with emaciation and respiratory disease in Guangxi province, China. The main pathogens were detected via PCR from lymph samples, and then PCV2-single positive samples were used to inoculate with PK-15 cells. After successive generations, the isolate was subsequently identified by polymerase chain reaction (PCR), immunofluorescence assay (IFA), Western blot (WB), and transmission electron microscopic (TEM). The full-length genome and genetic characterization of isolates were analyzed by Sanger sequencing. The TCID50 of the PCV2-GX-6 was determined by IFA, and the pathogenicity of PCV2 in BALB/c mice was analyzed via the mouse model.

RESULTS

The isolates were successfully isolated from clinical samples. The complete genome of PCV2-GX-4, PCV2-GX-6, PCV2-GX-7, PCV2-GX-11 and PCV2-GX-16 have been amplified, sequenced, and deposited in GenBank (accession no.: OR133747, OQ803314, OR133748, OR133749, OR133750). Homology and phylogenetic analysis with reference strains showed that the isolates belonged to the PCV2d genotype. The PCV2-GX-6 could be stably passaged more than 30 times in PK-15 cells. PCV2-GX-6 was identified by PCR, IFA, WB and TEM. The results of homology showed that PCV2-GX-6 was closely related to the reference strains PCV2-JS17-8 (GenBank accession no.: MH211363). Pathogenicity studies in mice have shown that PCV2-GX-6 can lead to growth inhibition of mice. Meanwhile PCV2-GX-6 caused the typical lesions of spleen, lung and kidney. The results of qPCR showed that PCV2 can effectively proliferate in the liver, spleen, lung, and kidney.

CONCLUSION

PCV2-GX-6 can successfully infect BLAB/c mice, effectively proliferate in major organs, and possessed high pathogenicity. In conclusion, combined with the genotype and pathogenicity of PCV2d currently prevalent, PCV2-GX-6 can be used as a candidate vaccine strain.

Pathogenic ecological characteristics of PCV2 in large-scale pig farms in China affected by African swine fever in the surroundings from 2018 to 2021

Porcine circovirus type 2 (PCV2) has been identified as the causal agent of postweaning multisystemic wasting syndrome (PMWS), an economically important multifactorial disease of the swine industry worldwide. This research designed a dual nested polymerase chain reaction (PCR) detection method to simultaneously monitor porcine circovirus type 2 (PCV2) and PCV3. The limit of detection (LoD) of sensitivity for PCV2 and PCV3 was ten copies/mL for both viruses. There was no cross-reaction with any other porcine pathogens tested and no non-specific amplification. The coincidence and repetition rates were both 100%. Through the systematic and clinical sampling, 15,130 samples collected from 30 large-scale pig farms in eight provinces in China (including Hubei, Hunan, Henan, Jiangxi, Shanxi, Guangdong, Hainan, and Heilongjiang) were subjected to early warning surveillance and/or clinical diagnosis. These results revealed that the overall positive rates of PCV3 and PCV2 were 0 and 28.29%, respectively, with the lowest level recorded in Jiangxi province. The highest carrying rate was observed in Hainan province. Pigs at different ages displayed varying carrying rates for PCV: fattening pigs and gilts had the highest and the lowest carrying rates for PCV, respectively. In addition, the excretion rates for PCV of colostrum, semen, and nasal, anal, and vulval swabs were tested. The colostrum, anal swabs, and semen had higher excretion rates for PCV; these were followed by the vulval and nasal swabs that had excretion rates for PCV. Furthermore, a high blood virus-carrying rate was detected in moribund pigs, especially in pigs with fever and red skin. As to the virus-carrying rate in the pig organs received from clinical necropsy, the highest rate was found in placental tissue, followed by the kidneys, and the virus also was detected in lymphoid organs, liver, stomach, and intestines. The PCV2-positive samples were sequenced to reveal the molecular epidemic dynamics of PCV2. The results indicated four major branches, namely, PCV2a, PCV2b, PCV2c, and PCV2d, concerning PCV2 molecular epidemiology in China, with PCV2a, PCV2b, and PCV2d dominating. In conclusion, the results obtained in this study elucidated the molecular epidemiology, transmission, and positive blood samples of PCV and provided new ideas for developing comprehensive PCV control technologies to begin eliminating the disease caused by PCV by cleaning pig farms.

Carboxyl-Terminal Decoy Epitopes in the Capsid Protein of Porcine Circovirus Type 2 Are Immunogenicity-Enhancers That Elicit Predominantly Specific Antibodies in Non-Vaccinated Pigs

In the context of the carboxyl-terminus (C-terminus) of the capsid protein of porcine circovirus type 2a (PCV2a) and PCV2a vaccines, this study aimed to explore its unrevealing cryptic epitope and its relation to PCV2-infected herd immunity. To discover the C-terminus of the capsid protein of PCV2a, monoclonal antibodies (mAbs) were generated in this work. Two mAbs bound the two minimal linear epitopes (₂₂₉PPLKP₂₃₃ and ₂₂₈DPPLNP₂₃₃ (or ₂₂₉PPLNP₂₃₃)), which were located at the C-terminus of the capsid proteins of PCV2a and PCV2b, respectively. One mAb bound to the minimal linear epitope (₂₂₀QFREFNLK₂₂₇, peptide P82), but it neither bound the virus-like particle (VLP) of PCV2a nor produced positive staining in PCV2a-infected cells by immunofluorescence assay. Further, the residues 220-227 were not accessible on the surface of the VLP on the three-dimensional model, but the residues 228-231 extend toward the VLP exterior. Immunoassays were conducted in this study to screen anti-viral peptide-specific IgGs, which could differentiate vaccinated pigs from non-vaccinated ones. The data show two ₂₂₀QFREFNLKDPPLKP₂₃₃-containing peptides had a significantly higher binding reactivity with sera from PCV2-infected pigs in the control group than with sera from the VLP-vaccine group, particularly seen in sera from swine aged 15 weeks to 24 weeks. However, the peptide P82 had not this phenomenon in that test. This study confirmed that C-terminal epitopes play an important role in PCV2-induced decoy of swine humoral immunity.

Genotype Shift of Malaysian Porcine Circovirus 2 (PCV2) from PCV2b to PCV2d within a Decade

This paper aims to update the molecular status of porcine circovirus 2 (PCV2) in Malaysia. Firstly, the molecular detection rate of PCV2 in farm and sampled pig population were reported to be 83.78% (31/37 farms) and 83.54% (66/79 pigs) positive for PCV2, respectively. PCV2 was detected across all age groups, from fetuses, porkers to sows. Co-detection of PCV2 and PCV3 antigens was also reported at a rate of 28.77% (21/73). Secondly, PCV2 antigen was also detected in Malaysian abattoir lung samples: 18 out of 19 (94.74%) samples originating from clinically healthy finishers were tested positive. Further, this is the first study to confirm the circulation of PCV2 in the wild boar population roaming Peninsular Malaysia, where 28 out of 28 (100%) wild boar lung samples were found positive. One decade earlier, only genotype PCV2b was reported in Malaysia. This most recent update revealed that genotypes PCV2a, PCV2b and PCV2d were present, with PCV2d being the predominant circulating genotype. PCV2 cap gene nucleotide sequences in this study were found to be under negative selection pressure, with an estimated substitution rate of 1.102 × 10-3 substitutions/site/year (ssy).

Epidemiology and Genetic Diversity of PCV2 Reveals That PCV2e Is an Emerging Genotype in Southern China: A Preliminary Study

Porcine circovirus-associated disease (PCVAD), caused by porcine circovirus type 2 (PCV2), has ravaged the pig industry, causing huge economic loss. At present, PCV2b and PCV2d are highly prevalent genotypes worldwide, while in China, in addition to PCV2b and PCV2d, a newly emerged PCV2e genotype detected in the Fujian province has attracted attention, indicating that PCV2 genotypes in China are more abundant. A preliminary study was conducted to better understand the genetic diversity and prevalence of PCV2 genotypes in southern China. We collected 79 random lung samples from pigs with respiratory signs, from 2018 to 2021. We found a PCV2-positivity rate of 29.1%, and frequent co-infections of PCV2 with PCV3, Streptococcus suis (S. suis), and other porcine pathogens. All PCV2-positive samples were sequenced and subjected to whole-genome analysis. Phylogenetic analysis, based on the PCV2 ORF2 gene and complete genomes, found that PCV2 strains identified in this study belonged to genotypes PCV2a (1), PCV2b (6), PCV2d (10), and PCV2e (6). Importantly, PCV2e was identified for the first time in some provinces, including Guangdong and Jiangxi. Additionally, we found two positively selected sites in the ORF2 region, located on the previously reported antigenic epitopes. Moreover, codon 63, one of the positively selected sites, has different types of amino acids in different genotypes. In conclusion, this study shows that PCV2e is an emerging genotype circulating in southern China, which warrants urgent, specific surveillance to aid the development of prevention and control strategies in China.

Molecular Epidemic Characteristics and Genetic Evolution of Porcine Circovirus Type 2 (PCV2) in Swine Herds of Shanghai, China

Porcine Circovirus 2 (PCV2) is a crucial swine pathogen and considered a primary causative agent of porcine circovirus-associated diseases (PCVADs), posing a serious economic threat to the swine industry across globe. The world’s biggest agricultural conglomerates have teamed up to create giant commercial pig farms across Shanghai due to the proximity of this region to more affluent lean-pork markets. Since its discovery, PCV2 has displayed extraordinary genetic diversity, and its genome is swiftly evolving through a series of mutations and recombinations. However, limited information on epidemiology, molecular characteristics, vaccine cross-protection, and the co-infection rate of PCV2 with other lethal swine diseases can adversely impact the pig production in the region. To investigate the molecular epidemic characteristics and genetic evolution of PCV2, pigs with doubtful symptoms of PCVADs were sampled from various commercial pig farms with a history of PWMS and/or PDNS across Shanghai from 2014 to 2018. Our results revealed the coexistence of multiple PCV2 genotypes (PCV2b, PCV2e, and PCV2d) among Shanghai pig herds and dominance of PCV2d among them. We also found critical amino acid substitutions in epitope regions of important capsid proteins in PCV2 isolates involved in viral replication and host immune escape. Spotted mutations may favor the prevalence and survival of various PCV2 genotypes despite availability of commercial vaccines. This study also provides insight into the co-infection status of PCV2 with major lethal swine viral diseases such as PPV and PPRSV. Collectively, these investigations will contribute to understanding the molecular epidemiology and evolution of PCV2 across the region.

Novel Porcine Circoviruses in View of Lessons Learned from Porcine Circovirus Type 2-Epidemiology and Threat to Pigs and Other Species

Porcine circovirus type 2 (PCV2) plays a key role in PCV2-associated disease (PCVAD) etiology and has yielded significant losses in the pig husbandry in the last 20 years. However, the impact of two recently described species of porcine circoviruses, PCV3 and PCV4, on the pork industry remains unknown. The presence of PCV3 has been associated with several clinical presentations in pigs. Reproductive failure and multisystemic inflammation have been reported most consistently. The clinical symptoms, anatomopathological changes and interaction with other pathogens during PCV3 infection in pigs indicate that PCV3 might be pathogenic for these animals and can cause economic losses in the swine industry similar to PCV2, which makes PCV3 worth including in the differential list as a cause of clinical disorders in reproductive swine herds. Moreover, subsequent studies indicate interspecies transmission and worldwide spreading of PCV3. To date, research related to PCV3 and PCV4 vaccine design is at early stage, and numerous aspects regarding immune response and virus characteristics remain unknown.

Genetic Diversity and Prevalence of Porcine Circovirus Type 2 in China During 2000-2019

As the major pathogen for porcine circovirus-associated disease (PCVAD), porcine circovirus type 2 (PCV2) is no longer treated as an emerging virus anymore. The wide distribution of PCV2 infection in China causes huge economic losses in the swine industry. Currently, it is generally believed that PCV2 has eight genotypes (PCV2a to PCV2h), with PCV2a, PCV2b, and PCV2d being widely distributed. To comprehensively explore the genetic diversity and prevalence of PCV2 in China, PCV-2 sequences submitted from China in the GenBank database were retrieved. With a total of 714 PCV2 strains were retrieved, we found that early-submitted PCV2 sequences were mainly collected from coastal provinces in the southeast part of China, which may indicate PCV2 was initially circulating in those regions. From 2002 to 2008, PCV2b was the dominant prevalent genotype in those retrieved sequences. From 2009, PCV2d became the dominant genotype in those sequences, dropping a hint that a potential shift of PCV2b to PCV2d might occur in 2009, which is similar to the patterns at the global level. In addition to the PCV2a, PCV2b, and PCV2d genotypes, novel strains were also characterized. We further revealed that the amino acid sequences consistency of PCV2a Cap is higher than those in other genotypes. Together, this study provided clues for the possible prevalent genotypes and dynamics of genetic diversity in China from 2000 to 2019.

Efficacy of bivalent vaccines of porcine circovirus type 2 and Mycoplasma hyopneumoniae in specific pathogen-free pigs challenged with porcine circovirus type 2d

Background

Porcine circovirus type 2 (PCV2) and Mycoplasma hyopneumoniae (MHP) are economically significant pathogens in the pig industry. The use of combined vaccines against PCV2 and MHP is one of the most effective ways of protecting pigs from both diseases, and it has become a part of general management.

Objectives

This study evaluated the efficacy of two new bivalent vaccines of PCV2 and MHP (Myco-X and Myco-XD) in SPF pigs. Myco-X and Myco-XD are a combined vaccine of MHP with PCV2b and PCV2d, respectively.

Methods

Sixteen pigs were divided into four groups: Myco-X-vaccinated challenged, Myco-XD-vaccinated challenged, unvaccinated challenged, and unvaccinated unchallenged. Two milliliters of Myco-X were administered intramuscularly, and 0.5 mL of Myco-XD was injected intradermally at 3 wk of age. The pigs were challenged with virulent PCV2d via the intramuscular and intranasal route 4 wk post-vaccination.

Results

All vaccinated pigs showed effective reduction of the clinical signs, the PCV2d load in the blood and nasal swab samples, as well as lung and lymphoid tissue lesions in the challenge test. Compared to unvaccinated challenged animals, the vaccinated challenged animals showed significantly higher (p < 0.05) levels of anti-PCV2 IgG, PCV2d-specific interferon-γ (IFN-γ), and anti-MHP IgG.

Conclusions

Based on clinical, microbiological, serological, and pathological assessments, this study confirmed that both combined vaccines could protect pigs against PCV2 infection caused by PCV2d. On the other hand, further research on the efficacy evaluation of these new vaccines against the MHP challenge and PCV2d/MHP co-challenge is needed.

Expression profile of long non-coding RNAs in porcine lymphnode response to porcine circovirus type 2 infection

Porcine circovirus type 2 (PCV2) can cause various clinical diseases in pigs, resulting in huge losses for the pig farms all over the world. In order to develop a new strategy to control PCV2, it is essential to understand its mechanisms firstly, especially PCV2 interferes with the host's innate immunity. In the present study, lncRNA and mRNA expression profiles in porcine lymphnode response to PCV2 infection were deeply sequenced and analyzed. 3271 novel lncRNAs were identified in all. 1898 mRNAs and 282 lncRNAs showed differential expression between control and PCV2-infected groups. The bioinformatics analysis including lncRNA-mRNA co-expression network construction, as well as GO and KEGG pathway analysis focused on the DEGs was carried out. The results indicated that lncRNAs might participate in PCV2 infection-induced the pathogenesis of immunosuppression through regulating the host's immune responses, biological regulation, response to stimulus, cellular component organization or biogenesis and metabolism. And these differentially expressed lncRNAs might play important roles in response to PCV2 infection in the host's innate immune system. These findings provided a large-scale survey of dysregulated lncRNAs after PCV2 infection, especially the lncRNAs responded to host's innate immune within the lymphnode. This study will provide a novel insight into the lncRNAs' functions and the possible immunosuppressive mechanism induced by PCV2 infection. However, further research will be required to verify the characteristic function of the dysregulated lncRNAs.

One Dose of a Novel Vaccine Containing Two Genotypes of Porcine Circovirus (PCV2a and PCV2b) and Mycoplasma hyopneumoniae Conferred a Duration of Immunity of 23 Weeks

Porcine circovirus type 2 (PCV2) and Mycoplasma hyopneumoniae (Mhyo) are important swine pathogens for which vaccination is a key control strategy. Three separate studies were performed to evaluate the duration of immunity (DOI) conferred by a novel vaccine combining PCV2a/PCV2b and Mhyo into a ready-to-use formulation. In each study, three-week-old naïve piglets were vaccinated (Day 0) and challenged 23-weeks later (Day 159) with either PCV2a, PCV2b or Mhyo. Pigs were euthanized three-to-four-weeks post-challenge. Vaccinated pigs had significantly lower PCV2 viremia from Day 168 until Day 175 (PCV2a study) or until euthanasia (PCV2b study), respectively. Fecal shedding was significantly lower for PCV2a-challenged from Day 171 until Day 178, and for PCV2b-challenged from Day 172 until euthanasia. In the PCV2a challenge study, there were no differences among vaccinates and controls in terms of percent of pigs positive for PCV2 immunohistochemistry, histiocytic replacement, or lymphoid depletion. However, significant differences for immunohistochemistry and histiocytic replacement, not lymphoid depletion, were observed among vaccinates and controls following PCV2b challenge. Vaccination supposed a significant reduction in the mean percentage of Mhyo-like lesions in the lung. Percentages of lung tissues positive for Mhyo via immunohistochemistry were 49.3% and 67.1% for vaccinated and control groups, respectively. One dose of the novel PCV2a/PCV2b/Mhyo vaccine conferred robust protection against challenge 23-weeks later for all three fractions.

Emergence of porcine circovirus 2g (PCV2g) and evidence for recombination between genotypes 2g, 2b and 2d among field isolates from non-vaccinated pigs in Mizoram, India

The molecular genetics of fourteen Porcine Circovirus 2 (PCV2) isolates from non-vaccinated pigs that died of porcine circovirus associated disease (PCVAD) between 2012 and 2019 in the Mizoram state of North East India, was studied. The PCVAD in these pigs, that had shown characteristic clinical signs and lesions associated with post-weaning multi-systemic wasting syndrome and reproductive failure was confirmed with detection of PCV2 DNA in the tissue samples. Complete viral genomes of these fourteen field isolates were sequenced following in house developed overlapping PCR. The multiple sequence alignment of viral capsid proteins or the open reading frame 2 (ORF2) sequences showed highly conserved residues known for antibody recognition and genotype specificity, however, variations were noticed in the amino acid residues previously known as important for in vitro replication of PCV2. The phylogenetic analyses based on the complete genome sequences enabled identification of genotype PCV2g (9/14, 64.29%) for the first time in India along with genotypes PCV2d (3/14, 21.43%) and PCV2b (2/14, 14.29%). Further, recombination analyses showed evidence for recombination between the genotypes 2b, 2g and 2d. This is the first report on the prevalence of genotype PCV2g and natural inter-genotypic (2g-2b, 2g-2d and 2d-2g) recombinants in India. The findings indicate a non-vaccine driven, natural genotypic shift and signify the need for routine PCV2 surveillance and genotyping. Our analyses also provide a solid ground for future studies to understand the consequences of multiple PCV2 genotypes within a pig population with respect to vaccination, diagnostics and emergence of new genotypes.

Field evaluation of a sing-dose bivalent vaccine of porcine circovirus type 2b and Mycoplasma hyopneumoniae

BACKGROUND

The field efficacy of a bivalent vaccine containing porcine circovirus type 2b (PCV2b) and Mycoplasma hyopneumoniae was evaluated on three pig farms.

METHODS

Three pig farms were used, two of which had a history of subclinical PCV2 and clinical M. hyopneumoniae infections between 84 and 126 days of age while concurrent porcine circovirus-associated disease and clinical M. hyopneumoniae infection between 70 and 105 days of age. Each farm vaccinated pigs with a single dose of a bivalent vaccine at 10 days of age while unvaccinated pigs were administered a single dose of phosphate buffered-saline at the same age.

RESULTS

Vaccination improved growth performance and reduced clinical scores significantly (p < .05) when compared with unvaccinated animals. The amount of PCV2d loads in blood and M. hyopneumoniae loads in nasal swabs of vaccinated animals were also significantly lower (p < .05) when compared with unvaccinated animals. Immunologically, vaccinated groups elicited a significantly higher (p < .05) level of protective immunity against PCV2d such as neutralizing antibodies and interferon-γ secreting cells (IFN-γ-SC), as well as protective immunity against M. hyopneumoniae such as IFN-γ-SC when compared with unvaccinated animals. Pathologically, vaccination significantly lowered (p < .05) the scores of M. hyopneumoniae-induced pneumonia and PCV2-associated lymphoid lesions when compared with unvaccinated animals.

CONCLUSIONS

The evaluated bivalent vaccine provided good protection against PCV2d and M. hyopneumoniae infection under field conditions.

A Dual Swine Challenge With Porcine Circovirus Type 2 (PCV2) and Mycoplasma hyopneumoniae Used to Compare a Combination of Mixable Monovalent PCV2 and Monovalent M. hyopneumoniae Vaccines With a Ready-to Use PCV2 and M. hyopneumoniae Bivalent Vaccine

The present study evaluated the efficacy of swine vacciation using a combination of mixable monovalents for porcine circovirus type 2 (PCV2) and Mycoplasma hyopneumoniae against a ready-to-use bivalent vaccine under experimental conditions. Pigs at 21 days of age were administered either a combination of two mixable monovalent vaccines or a bivalent vaccine containing PCV2 and M. hyopneumoniae. Vaccination was followed with an M. hyopneumoniae challenge at 42 days of age (−14 days post challenge, dpc) and a PCV2d challenge at 56 days of age (0 dpc). Each vaccinated and challenged group was compared with the unvaccinated and challenged group for clinical, microbiological, immunologic, and pathologic differences. Clinically, two vaccinated and challenged groups showed minimal respiratory diseases that was characterized by occasionally coughing and sneezing. A significant difference was not calculated in the average daily weight gain, nasal shedding of M. hyopneumoniae, and pathological lesions between two vaccinated and challenged groups. A combination of two monovalent vaccines mixed into a combo prior to vaccination followed by challenge resulted in increased numbers of PCV2d-specific interferon-γ secreting cells at 21 dpc and a significant reduction in PCV2d viremia at 14 dpc when compared with the ready-to-use bivalent-vaccinated and challenged groups. These results offer supporting evidence that vaccination during the weaning to finishing period against M. hyopneumoniae and PCV2 is efficacious for controlling diseases caused by these two pathogens.

The Monoclonal Antibody Recognized the Open Reading Frame Protein in Porcine Circovirus Type 2-Infected Peripheral Blood Mononuclear Cells

The purpose of this study in the context of the open reading frame 3 (ORF3) protein of porcine circovirus type 2 (PCV2) was especially its location and its relation to the capsid protein and the apoptosis protein in PCV2-infected porcine peripheral blood mononuclear cells (PBMCs). To detect the ORF3 protein, monoclonal antibodies (mAbs) were generated in this study. The mAb 7D3 binds to the ORF3 peptide (residues 35–66) and the native ORF3 protein in PCV2-infected PBMCs, as shown by immunofluorescence assay (IFA). The data show that 3–5% of PBMCs were positive for ORF3 protein or p53 protein. Further, 78–82% of PBMCs were positive for the capsid. This study confirmed the ORF3 protein not only colocalized with the capsid protein but also colocalized with the p53 protein in PBMCs. Immunoassays were conducted in this study to detect the capsid protein, the ORF3 protein, anti-capsid IgG, and anti-ORF3 IgG. The data show the correlation (r = 0.758) of the ORF3 protein and the capsid protein in the blood samples from the PCV2-infected herd. However, each anti-viral protein IgG had a different curve of the profile in the same herd after vaccination. Overall, this study provides a blueprint to explore the ORF3 protein in PCV2-infected PBMCs.

Porcine circovirus type 2 (PCV2) genotyping in Austrian pigs in the years 2002 to 2017

Background

Eight different PCV2 genotypes with varying prevalence and clinical impact have been described so far. PCV2 infection is still widespread among the vaccinated population and several experimental studies have clearly demonstrated that there is no induction of a 100% cross-protective immunity between the PCV2 genotypes. Hence, PCV2a-based vaccines may be ineffective. In this longitudinal study, the PCV2 genotype and haplotype evolution in Austria in the years 2002 to 2017 was investigated by phylogenetic analysis of 462 bp-long sequences of the capsid protein gene (ORF2). The obtained findings may be of practical relevance for the future development of vaccination strategies.

Results

One hundred thirty four of a total of 161 formalin-fixed and paraffin wax-embedded samples could be sequenced successfully. There was no significant influence of storage time on sequencing success or quality. PCV2a (8.2%), PCV2b (77.6%), PCV2d (13.4%), and PCV2g (0.8%) were found. PCV2d was first detected as early as in 2004. PCV2g was described once in 2009. Both global PCV2 genotype shifts were observed. PCV2a occurred with a low prevalence during the first study years only in samples from non-vaccinated swine herds and was gradually replaced by PCV2b until 2011. PCV2b was the most prevalent genotype over the whole study period and was detected in samples from vaccinated and non-vaccinated herds. During the last two study years, the prevalence of PCV2d increased, although at this point almost all herds were vaccinated. The haplotype diversity was high, but the nucleotide diversity was low. Especially for genotype PCV2b, an increase in haplotype diversity could be described during the first study years.

Conclusion

Extensive PCV2a-derived vaccination resulted in a reduction of prevalence and in a stabilization of genotype PCV2a, whereas genotypes PCV2b and PCV2d evolved as a consequence of natural and vaccination-induced selection. An ongoing virus circulation may be the result of reduced vaccine-induced protection.

Genetic Diversity of Porcine Circovirus Isolated from Korean Wild Boars

In Korea, three genotypes of porcine circovirus type 2 (PCV2a, PCV2b, and PCV2d) have been identified on domestic pig farms, while two genotypes (PCV2a and PCV2b) have been identified in wild boar populations. Here, we investigated genotype diversity and genotypic shift in 91 PCV2 isolates from 1340 wild boars captured in South Korea between 2013 and 2017. Phylogenetic analyses based on the complete ORF2 showed that the 91 PCV2 strains were detected as four genotypes by qPCR screening assay: PCV2a (2.2%, 2/91), PCV2b (16.5%, 15/91), PCV2d (80.2%, 73/91), and PCV2h (1.1%, 1/91). Only one intergenotype recombinant event was detected between PCV2 ORF2 in wild boars (PCV2b) and domestic pigs (PCV2a). Amino acid positions 86–89 within ORF2, which distinguishes the different genotypes, were conserved in all PCV2 genotypes isolated from South Korean wild boars, including TNKI in PCV2a/PCV2h, SNPR in PCV2b, and SNPL in PCV2d. The estimated nucleotide substitution rates in the ORF2 region of viruses from South Korean wild boars and domestic pigs were 5.8145 × 10⁻⁴ and 4.5838 × 10⁻⁴ substitutions per site per year (s/s/y), respectively. The times to the most recent common ancestor (tMRCA) for South Korean domestic pig PCV2 were 1937 (PCV2a), 1972 (PCV2b), 1999 (PCV2d-1), and 2000 (PCV2d-2). By contrast, the tMRCA for South Korean wild boar PCV2b and PCV2d were 1989 and 2001, respectively. Thus, the PCV2d genotype is prevalent among South Korean wild boars and domestic pigs.

Genomic analysis of porcine circovirus type 2 from southern China

Background

Porcine circovirus type 2 (PCV2) is recognized as virulent porcine pathogen and has been linked to porcine circovirus diseases (PCVD). However, there remain many unknowns regarding the spread and epidemic growth of PCV2.

Methods

To assess the genetic diversity of PCV2 in the southern China, a total of 92 sequences of PCV2 strains from this region were retrieved from GenBank and were subjected to amino acid variation and phylogenetic analyses together with 28 representative sequences, based on the sequence of the ORF2 gene, from different swine‐producing countries.

Results

All 92 PCV2 strains shared between 93.7% and 100% sequence similarity and could be divided into four genotypes (PCV2a, PCV2b, PCV2d and PCV2h), of which PCV2d had surpassed PCV2b and became the most prevalent PCV2 genotype in this region. Alignment of the deduced amino acid sequences of the capsid protein revealed that the obtained PCV2 strains possess two major heterogenic regions/hypervariable regions (positions 52–68 and 185–191), which were within or close to the epitopic regions in the capsid (Cap) protein. Meanwhile, the 92 PCV2 sequences also show evidence of at least five unique recombination events.

Conclusion

The data in this study indicate that the PCV2 strains in the southern China are undergoing constant genetic variation and that the predominant strain and its antigenic epitopes in this area have been gradually changing in recent years.

Free to Circulate: An Update on the Epidemiological Dynamics of Porcine Circovirus 2 (PCV-2) in Italy Reveals the Role of Local Spreading, Wild Populations, and Foreign Countries

Porcine circovirus 2 (PCV-2) is one of the most impactful and widespread pathogens of the modern swine industry. Unlike other DNA viruses, PCV-2 is featured by a remarkable genetic variability, which has led to the emergence and recognition of different genotypes, some of which (PCV-2a, 2b, and 2d) have alternated over time. Currently, PCV-2d is considered the most prevalent genotype, and some evidence of differential virulence and vaccine efficacy have been reported. Despite the potential practical relevance, the data on PCV-2 epidemiology in Italy are quite outdated and do not quantify the actual circulation of this genotype in Italy. In the present study, 82 complete ORF2 sequences were obtained from domestic pigs and wild boars sampled in Northern Italy in the period 2013–2018 and merged with those previously obtained from Italy and other countries. A combination of phylogenetic, haplotype network, and phylodynamic analyses were used to genotype the collected strains and evaluate the temporal trend and the spatial and host spread dynamics. A rising number of PCV-2d detections was observed in domestic pigs, particularly since 2013, reaching a detection frequency comparable to PCV-2b. A similar picture was observed in wild boars, although a lower sequence number was available. Overall, the present study demonstrates the extreme complexity of PCV-2 molecular epidemiology in Italy, the significant spread across different regions, the recurrent introduction from foreign countries, and the frequent occurrence of recombination events. Although a higher viral flux occurred from domestic to wild populations than vice versa, wild boars seem to maintain PCV-2 infection and spread it over relatively long distances.

Phylogenetic analysis of porcine circovirus type 2 (PCV2) between 2015 and 2018 in Henan Province, China

Background

Porcine circovirus type 2 (PCV2) is the pathogen of porcine circovirus associated diseases (PCVAD) and one of the main pathogens in the global pig industry, which has brought huge economic losses to the pig industry. In recent years, there has been limited research on the prevalence of PCV2 in Henan Province. This study investigated the genotype and evolution of PCV2 in this area.

Results

We collected 117 clinical samples from different regions of Henan Province from 2015 to 2018. Here, we found that the PCV2 infection rate of PCV2 was 62.4%. Thirty-seven positive clinical samples were selected to amplify the complete genome of PCV2 and were sequenced. Based on the phylogenetic analysis of PCV2 ORF2 and complete genome, it was found that the 37 newly detected strains belonged to PCV2a (3 of 37), PCV2b (21 of 37) and PCV2d (13 of 37), indicating the predominant prevalence of PCV2b and PCV2d strains. In addition, we compared the amino acid sequences and found several amino acid mutation sites among different genotypes. Furthermore, the results of selective pressure analysis showed that there were 5 positive selection sites.

Conclusions

This study indicated the genetic diversity, molecular epidemiology and evolution of PCV2 genotypes in Henan Province during 2015–2018.

Emergence of a novel recombinant porcine circovirus type 2 in China: PCV2c and PCV2d recombinant

Porcine circovirus type 2 (PCV2) has been causing huge economic losses in Chinese swine herds since it was first identified in China in 1999. Genotypes of PCV2 except for PCV2c coexist in swine herds in China, which may facilitate virus recombination. In the current study, six novel PCV2 strains were detected in China, and these strains shared high nucleotide similarity of the Rep gene with the PCV2c strain DK1987PMWSfree and high homology of the Cap gene with PCV2d. Genome sequence analysis revealed that the complete genomes of these strains were 1767 nucleotides (nt) in length and shared 99.8%-99.9% nucleotide identity with each other and 91.7%-98.7% with representative strains. Phylogenetic analysis, sequencing analysis, base-by-base comparisons and comprehensive recombination analysis demonstrated that these six strains originated from recombination within the Rep gene between PCV2c and PCV2d strains. Surprisingly, further investigation through theoretical recombination analysis of Chinese PCV2 GenBank sequences showed that these novel patterns of recombinant PCV2 strains have been generated since 2010. Collectively, our findings provide additional evidence of inter-genotypic recombination of PCV2.

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

Porcine circovirus type 2 (PCV2) is an important pathogen that causes significant economic losses in the swine industry worldwide. Five major PCV2 genotypes have been identified, including PCV2a, PCV2b, PCV2c, PCV2d, and PCV2e. To investigate the prevalence and phylodynamics of the different PCV2 genotypes in Taiwan, 214 PCV2 ORF2 sequences from Taiwan and other countries were analyzed. Genotypic differences were observed among PCV2a, 2b, and 2d at amino acid position 89 in ORF2, with isoleucine (I), arginine (R), and leucine (L), respectively. Similar to other countries, a genotypic shift was also observed in Taiwan, where the predominant genotype shifted from PCV2b to 2d after 2010. The estimated nucleotide substitution rate of Taiwanese strains in the ORF2 region was 8.467 × 10⁻⁴ substitutions per site per year. This rapid evolution rate of PCV2 may lead to the genotypic shift observed in Taiwan. The times to the most recent common ancestor (TMRCA) for PCV2a, -2b, and -2d-2 was dated to 1970, 1992 and 2004, respectively. Thus, the PCV2a, -2b, and -2d genotypes were already present in Taiwan before the introduction of the PCV2 vaccine.

Truncated Rep protein of porcine circovirus 2 (PCV2) caused by a naturally occurring mutation reduced virus replication in PK15 cells

BACKGROUND

Porcine circovirus 2 (PCV2) is the causative agent of porcine circovirus-associated diseases (PCVADs). The infection of PCV2 is widespread and has serious consequence, thereby causing significant economic losses in the swine industry worldwide. Previously, we found that a strain named YiY-3-2-3 has a naturally occurring point mutation (G⁷¹⁰ to A⁷¹⁰) in ORF1 region, which leads to a shorten product of the rep gene (945 to 660 base pair). Importantly, the Rep protein is responsible for genome replication of PCV2. To explore the effects of this mutation on the PCV2 replication, in the current study we constructed infectious clone of this IF-YiY-3-2-3, as well as those of its two parental strains of IF-YiY-3-2-1 and IF-YiY-3-2-10. Subsequently, these infectious clones which have 1.1 copy of PCV2 genome of their corresponding strains were transfected into PK15 cells to obtain rescued viruses, respectively.

RESULTS

Though all of the three infectious clones could be rescued, the copy number and infectivity of these rescued viruses were significantly different, as analyzed by fluorescence quantitative PCR, Tissue culture infectious dose 50 (TCID₅₀), and indirect immunofluorescence assay (IFA). Notably, whether the PCV2 copy number, viral titer or the infectivity of rescued viruses from infectious clone IF-YiY-3-2-3 was significantly less than those of its parental clones. Meanwhile, the spatial structure of the Rep protein from the IF-YiY-3-2-3 displayed an apparent truncation at the C-terminal.

CONCLUSIONS

These findings therefore suggest that the Rep protein with truncated C-terminal would reduce virus replication and infectivity, and there might also exist both favorable and unfavorable mutations in the ORF1 of PCV2 in the process of its evolution.

Genetic analysis of porcine circovirus type 2 (PCV2) strains between 2002 and 2016 reveals PCV2 mutant predominating in porcine population in Guangxi, China

Background

Porcine circovirus 2-associated disease (PCVAD) is acknowledged as one of the most economically important diseases for the swine industry worldwide. The aim of this study was to characterize and determine the genetic diversity of PCV2 in the porcine population of Guangxi, China.

Methods

The full length genome and open reading frame 2 (ORF2) of 95 PCV2 strains collected from the tissues and sera of pigs that had either died as a result of PCVAD or did not exhibit disease symptoms were analyzed.

Results

The results of multiple sequence alignments showed that there is considerable diversity among the PCV2 ORF2 sequences. Phylogenetic analyses based on the complete genome showed that current PCV2 strains in this study could be divided into PCV2a (1/95), PCV2b (39/95), PCV2d (43/95), PCV2e (10/95) and PCV2h (2/95). Among the 5 sub-genotypes, PCV2b was dominant in the porcine population from 2002 to 2008. The newly identified sub-genotype, PCV2d, was seen from 2003 and has increased every year. PCV2b and PCV2d formed two predominant genetic groups circulating in southern China between 2009 and 2013 and the sub-genotype PCV2d has become the dominant virus in China since 2014.

Conclusions

This study reveals the complex genetic diversity of PCV2 and improves our understanding regarding the epidemiological trends of PCV2 sub-genotypes in China.

Electronic supplementary material

The online version of this article (10.1186/s12917-019-1859-z) contains supplementary material, which is available to authorized users.

First detection and phylogenetic analysis of porcine circovirus type 2 in raccoon dogs

Background

Porcine circovirus type 2 (PCV2) is a major emerging virus of porcine circovirus-associated disease (PCVAD), which has brought huge economic losses to the global pig industry. Pigs are well known as the natural reservoir of PCV2. Recently, many researchers have revealed PCV2 could infect many other mammals like mice, calves, minks, dogs and goats. In 2018, our laboratory has admitted six cases of raccoon dogs from Qinhuangdao city of China, which were characterized by inappetence, lethargy, depression, abortion, and sterility.

Results

At last, six raccoon dog-origin PCV2 strains were isolated in this study. Pairwise-sequence comparisons demonstrated that the six raccoon dog-origin PCV2 strains shared a nucleotide similarity of 92.1–99.8% among 40 PCV2 representative strains. Phylogenetic analysis indicated these PCV2 isolates belonged to Chinese epidemic genotypes PCV2b and PCV2d. And aborted or sterile symptom was significantly associated with PCV2 infection in raccoon dogs by the chi-square test (χ² = 87.3, p < 0.001). The retrospective study revealed that raccoon dog-origin PCV2 strains shared 100% sequence similarity with the PCV2 stains isolated from pig farms around these raccoon dog farms, respectively.

Conclusion

In this study, the first supported evidence of PCV2 prevalence in raccoon dog farms of China was documented. PCV2 may be one of the most significant causative agents resulting in the reproductive failure of farmed raccoon dogs, implying that PCV2 could transmit from pigs to raccoon dogs. That indicated that PCV2 cross-species transmission will be a serious threat to China’s fur animal farming industry.

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.

Evaluation of a porcine circovirus type 2a (PCV2a) vaccine efficacy against experimental PCV2a, PCV2b, and PCV2d challenge

The objective of this study was to compare the efficacy of a commercial porcine circovirus type 2a (PCV2a) subunit vaccine against experimental PCV2a, PCV2b, and PCV2d challenge. A total of 105 pigs were randomly divided into 7 groups (15 pigs per group). At 21 days old the pigs were intramuscularly administered the PCV2a vaccine as a 1.0 mL dose. Four weeks following vaccination, pigs were challenged with either Korean PCV2a, PCV2b, or PCV2d. All vaccinated pigs showed a significant (P <  0.05) reduction of clinical signs, PCV2 viremia, lymphoid lesions, and lymphoid PCV2 antigen levels compared to unvaccinated control pigs. Vaccination resulted also in significantly higher (P <  0.05) titers of neutralizing antibody against PCV2, and an increase in the frequency of PCV2-specific interferon-γ secreting cells (IFN-γ-SC). The vaccine showed similar protection among the vaccinated groups regardless of the genotype of the challenge. Interestingly, vaccinated pigs had higher levels of neutralizing antibody titers against PCV2a compared to PCV2b or PCV2d while the number of PCV2a-, PCV2b-, and PCV2d-specific IFN-γ-SC were similar. Taken together, the results presented here demonstrate that a PCV2a vaccine can be effective against experimental PCV2a, PCV2b, and PCV2d challenge.

Structural roles of PCV2 capsid protein N-terminus in PCV2 particle assembly and identification of PCV2 type-specific neutralizing epitope

Postweaning multisystemic wasting disease (PMWS) in piglets caused by porcine circovirus type 2 (PCV2) is one of the major threats to most pig farms worldwide. Among all the PCV types, PCV2 is the dominant genotype causing PMWS and associated diseases. Considerable efforts were made to study the virus-like-particle (VLP) assembly and the specific PCV2-associated epitope(s) in order to establish the solid foundation for engineered PCV2 vaccine development. Although the N-terminal fragment including Nuclear Localization Signal (NLS) sequence seems important for recombinant PCV2 capsid protein expression and VLP assembly, the detailed structural and functional information regarding this important fragment are largely unknown. In this study, we report crystal structure of PCV2 VLP assembled from N-terminal NLS truncated PCV2 capsid protein at 2.8 Å resolution and cryo-EM structure of PCV2 VLP assembled from full-length PCV2 capsid protein at 4.1Å resolution. Our in vitro PCV2 VLP assembly results show that NLS-truncated PCV2 capsid protein only forms instable VLPs which were easily disassembled in solution, whereas full-length PCV2 capsid protein forms stable VLPs due to interaction between ¹⁵PRSHLGQILRRRP²⁷(α-helix) and ³³RHRYRWRRKN⁴²(NLS-B) in a repeated manner. In addition, our results also showed that N-terminal truncation of PCV2 capsid protein up to 27 residues still forms PCV2 particles in solution with similar size and immunogenicity, while N-terminal truncation of PCV2 capsid protein with more than 30 residues is not able to form stable PCV2 particles in solution, demonstrating the importance of interaction between the α-helix at N-terminal and NLS-B in PCV2 VLP formation. Moreover, we also report the cryo-EM structure of PCV2 VLP in complex with 3H11-Fab, a PCV2 type-specific neutralizing antibody, at 15 Å resolution. MAb-3H11 specifically recognizes one exposed epitope located on the VLP surface EF-loop (residues 128–143), which is further confirmed by PCV1-PCV2 epitope swapping assay. Hence, our results have revealed the structural roles of N-terminal fragment of PCV2 capsid protein in PCV2 particle assembly and pinpointed one PCV2 type-specific neutralizing epitope for the first time, which could provide clear clue for next generation PCV2 vaccine and diagnostic kits development.

Porcine circovirus type 2 (PCV2) is considered as one of the most wide-spread pathogens threatening swine production by causing postweaning multisystemic wasting disease (PMWS) in piglets worldwide. Several VLP-based PCV2 vaccines are commercially available which significantly reduce the viral burden and virally induced lesions. However, prophylactic efficacy of VLP-based PCV2 vaccine largely relies on the correct VLP assembly from the individual PCV2 capsid protein. Notably, limited structural information of PCV2 N-terminal fragment containing arginine-rich patches significantly delays our understanding of PCV2 assembly at the molecular level, and the lack of solid evidence in identification of PCV2 type-specific epitope delays the development of PCV2 type-specific diagnosis kits. In this study, through the combination of structural and immunological approaches, we are able, for the first time, to disclose the structural details of the N-terminal Nuclear Localization Signal (NLS) region of PCV2 capsid protein. We show that the interaction between the α-helix from one capsid protein and the NLS-B from an adjacent capsid protein within the pentamer stabilizes the assembled PCV2 VLP in solution. Moreover, by the combination of structural determination and biochemical mapping, we have identified that a short linear sequence (¹³⁴KATALT¹³⁹) located within PCV2 EF-loop is a unique PCV2 type-specific neutralizing epitope. Therefore, our work has revealed the detailed structural information of PCV2 particle assembly and a PCV2 type-specific neutralizing epitope, which should provide insightful information for virus-host interaction studies and next-generation PCV2 vaccine and type-specific diagnostic kits development.

First detection and genetic analysis of fox-origin porcine circovirus type 2

Porcine circovirus type 2 (PCV2) is a causative agent of porcine circovirus-associated disease (PCVAD), which is a serious problem in the swine industry worldwide. In recent years, nonporcine-origin PCV2 has attracted more and more attention of the researchers. This study reported on the first identification of PCV2 in farmed foxes with reproductive failure. Three fox-origin PCV2 strains were successfully isolated, sequenced, and designated as FoxHB1, FoxHB2, and FoxHB3 respectively. Pairwise-sequence comparisons of the complete genomes revealed that three fox-origin PCV2 strains had nucleotide identities varied from 91.9% to 99.7% with representative strains of PCV2 different genotypes. Meanwhile, phylogenetic analysis based on complete genomes of 44 PCV2 strains indicated that the fox-origin PCV2 strains belonged to Chinese epidemic genotypes PCV2b and PCV2d. These results provided the first supported evidence that PCV2 could infect foxes, implying that the cross-species transmission of PCV2 would be a big threat to Chinese fur animal-bearing industry.

Longitudinal comparison of the humoral immune response and viral load of Porcine Circovirus Type 2 in pigs with different vaccination schemes under field conditions

Background: Porcine Circovirus type 2 (PCV2) infections are distributed worldwide and cause Porcine Circovirus Associated Disease (PCVAD). To minimize the impact of PCV2 infection on swine health and production, different vaccination schemes have been used since 2006. However, the association between vaccination schemes, virus load and disease under field conditions are not completely understood. Therefore, the objective of this study was to compare the effect of two different PCV2 vaccination schemes on the humoral response and PCV2 load in pigs after weaning under field conditions.

Methods: Two commercial pig farms (Farm A and B), endemically infected with PCV2, which were using two different PCV2 subunit vaccinations schemes for sow, gilts and piglets, were selected. We designed a longitudinal study and measured IgG levels by ELISA and virus load by quantitative PCR in pigs after weaning. Forty 3-week old piglets were randomly selected at weaning and followed for 20 weeks. IgG levels and virus loads were compared within and between farms and considered statistically different if the non-parametric Wilcoxon-test p value was lower than 0.05.

Results: We found that low virus loads were maintained in pigs from both farms regardless of the vaccination scheme used (p>0.05). However, there was significant difference in the mean IgG levels observed over time (p<0.05) while there were no significant differences in viral loads. This suggests that different humoral immune response is not associated with different virus loads observed over time.

Conclusions: These results are important because they can help to prevent PCV2 infections using different vaccination schemes to minimize the effect of PCVAD on swine health and production.

The prevalence and genetic characteristics of porcine circovirus type 2 and 3 in Korea

BACKGROUND

Porcine circovirus-associated diseases (PCVAD), caused by porcine circovirus type 2 (PCV2), threaten the pig industry worldwide. Five genotypes of PCV2 were recently identified: PCV2a, PCV2b, PCV2c, PCV2d and PCV2e. In addition, a novel porcine circovirus from a case of a sow with dermatitis, nephropathy syndrome and reproductive failure has been identified based on metagenomic analysis and classified as porcine circovirus type 3 (PCV3). Therefore, the current study was conducted to determine the prevalence and genetic characteristics of PCV2 and PCV3 in clinical samples.

RESULTS

A total of 471 samples (161 tissue samples of lungs and lymph nodes from 34 farms and 310 serum samples from 47 farms) were tested for PCV2. Among them, 171 samples from 59 farms that had been positive for PCV2 were genotyped. Another 690 samples (296 tissue samples of lungs and lymph nodes from 91 farms, 108 samples of aborted foetuses from 26 farms, and 286 serum samples from 47 farms) were tested for PCV3. Based on PCV2 genotyping results, PCV2d was the most prevalent genotype (107 of 171 samples), and co-infections with combinations of PCV2a, 2b and 2d were identified in 48 samples from 17 farms. A total of 14 samples from 11 farms were also positive for both PCV2 and PCV3. For PCV3, 57 samples (9.8%) from 32 farms (23.2%) were positive. Among the 108 aborted foetuses from 26 farms, only 2 samples were positive for PCV3. Based on sequence comparisons, PCV2d shares 89.6-91.0% and 93.2-94.3% homology with PCV2a and PCV2b, respectively; 98.6-100% homology is shared among PCV2d strains. The PCV3 strains identified in this study share 98.0-99.5% homology.

CONCLUSIONS

Our study concludes that PCV2d has become the most predominant genotype in Korea. PCV3 was also identified in clinical samples, though no significant association with clinical symptoms was observed in PCV3-positive cases.

The evidence of occurrence of porcine circovirus 2 isolation and characterization in Kazakhstan

This report describes the first isolation and characterization of porcine circovirus 2 (PCV2) in the Republic of Kazakhstan. The virus was isolated from a dead piglet that did not exhibit any typical clinical symptoms of porcine circovirus disease at a pig factory in North Kazakhstan oblast (region). The isolated virus belongs to genotype 2 (PCV2) and shares 96.6% sequence homology with one isolate and two strains from China and two French strains in group 1, cluster 1ab and 96.4% homology with two strains isolated in China and one strain from Hungary. Electron microscopy revealed the isolated virus had the typical morphological structure of PCV. This is the evidence of occurrence of porcine circovirus 2 isolation and characterization in Kazakhstan.

High prevalence of PCV2d in Hunan province, China: a retrospective analysis of samples collected from 2006 to 2016

Porcine circovirus 2 (PCV2) has been widely prevailing in China since the first report in 2001, causing huge economic losses to the pig industry. In the present study, 674 samples were collected from 2006 to 2016 in Hunan province, and 62% were positive for PCV2. An increase was observed from 2006 to 2011 (72.1%-89.1%), and a decrease was observed from 2012 to 2016 (78.9%-36.8%). The prevalence of genotype PCV2a, PCV2b, and PCV2d was 0, 44.7% and 67%, respectively. During 2006-2007, PCV2b was the main genotype circulating in Hunan, while, in 2008, PCV2d became the predominant one. Coinfection with PCV2b and PCV2d was observed frequently, and the positive rates of coinfection ranged from 6.3% to 18.9% during 2006-2016. The complete genome was sequenced for 54 positive samples, and four were identified as PCV2b-1, 22 as PCV2b-2, four as PCV2d-1 and 24 as PCV2d-2, based on phylogenetic analysis of the complete genome and ORF2 region. Recombination analysis using the complete genome sequences of these isolates revealed a high recombination rate of 27.7% (17/54), and showed that recombination occurred mainly in the ORF1 region. This shows that the prevalence of PCV2 has clearly decreased in recent years and that PCV2d has become a predominant genotype since 2008. In addition, frequent recombination events were observed in the PCV2 isolates from Hunan, China.

Detection of PCV2e strains in Southeast China

Porcine circovirus 2 (PCV2) has been prevalent in swine herds in China since 2002, causing severe economic loss to the pig industry. The number of live pigs in southeast China is > 20 million. Since information on the genetic variation of PCV2 in the Fujian province is limited, the objective of the present work was to investigate the epidemiological and evolutionary characteristics of PCV2 in southeast China from 2013 to 2017. Of the 685 samples collected from 90 different swine herds from 2013 to 2017, 356 samples from 84 different swine herds were positive for PCV2. PCV2a, PCV2b, PCV2d, and PCV2e co-existed in the Fujian province, with PCV2d being the predominant circulating strain in swineherds and PCV2e being reported for the first time in China. Strikingly, PCV2-FJ-water DNA comes from contaminated river water and not infected animals. Sequence comparison among all isolates indicated that 95 isolates shared approximately 78.7%–100% nucleotide identity and 74.5%–100% amino acid identity for open reading frame 2 (ORF2). Amino acid alignment showed that the Cap protein of PCV2e differed markedly from those of PCV2a, PCV2b, PCV2c, and PCV2d. These results indicated that various PCV2 genotypes exist in China, and that PCV2 is continuously evolving, leading to rapid emergence of new variant stains.

Phylogenetic analysis of two goat-origin PCV2 isolates in China

Complete genome characterization of non-porcine origin Porcine circovirus type 2 (PCV2) was first described in 2014 in China. In the present study, we first identified PCV2 nucleotides in goat samples and the prevalence of PCV2 in goat was 6.15%. However, only two new strains, Goat2014-4 and Goat2014-5, could be completely sequenced. The genome of the strain Goat2014-4, which collected from the goat infected with PPRV, contains 1766 nt; strain Goat2014-5, which originated from a healthy goat, is comprised of 1767 nt. The results showed that they shared the highest nucleotide identity with BDH and the lowest similarity with DK1980PMWSfree strain and they belonged only to genotype PCV2d. Meanwhile, they shared higher homology with porcine-origin PCV2 strains than others. Moreover, a detailed analysis of the capsid amino acid sequences revealed that there were distinct differences for goat2014-4 (708 bp) and goat2014-5 (705 bp); strain Goat2014-4 showed an elongation of two amino acids, and strains Goat2014-5 showed an elongation of one amino acid compared with other reference strains. This is the first report of the genetic analysis of goat-origin PCV2 isolates. It also provides an additional supported evidence for cross-species transmission of PCV2.

Retrospective study of porcine circovirus type 2 infection reveals a novel genotype PCV2f

Porcine postweaning multisystemic wasting syndrome (PMWS) caused by porcine circovirus type 2 (PCV2) is a disease causing severe economic losses annually worldwide to the pig industry. PCV2 infection was first reported in China in 2000, and currently has three major genotypes, PCV2a, b and d, circulating in this country. To further elucidate the origin and prevalence of PCV2 in China, 123 clinical pig tissue samples collected in 25 provinces between 1990 and 1999 were analysed by PCV2-specific PCR, resulting in identification of 23 PCV2 strains collected between 1996 and 1999. Phylogenetic analysis based on the nucleotide sequences of open reading frame 2 (ORF2) showed that 20 of the 23 grouped within PCV2a, while the remaining three strains formed an independent clade, so far unreported and therefore named PCV2f. This genotype shared lower sequence identity with other known genotypes. This study provides further understanding of the genetic diversity and evolution of PCV2 and has tracked PCV2 infection in China back to 1996 rather than 2000.

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.

Genetic diversity of porcine circovirus type 2 (PCV2) in Thailand during 2009-2015

Porcine circovirus type 2 (PCV2), the essential cause of porcine circovirus associated disease (PCVAD), has evolved rapidly and it has been reported worldwide. However, genetic information of PCV2 in Thailand has not been available since 2011. Herein, we studied occurrence and genetic diversity of PCV2 in Thailand and their relationships to the global PCV2 based on ORF2 sequences. The results showed that 306 samples (44.09%) from 56 farms (80%) were PCV2 positive by PCR. Phylogenetic trees constructed by both neighbor-joining and Bayesian Inference yielded similar topology of the ORF2 sequences. Thai PCV2 comprise four clusters: PCV2a (5.5%), PCV2b (29.41%), intermediate clade 1 (IM1) PCV2b (11.03%) and PCV2d (54.41%). Genetic shift of PCV2 in Thailand has occurred similarly to the global situation. The shift from PCV2b to PCV2d was clearly observed during 2013-2014. The viruses with genetically similar to the first reported PCV2 in 2004 have still circulated in Thailand. The first Thai PCV2b and PCV2d were closely related to the neighboring countries. The haplotype network analysis revealed the relationship of PCV2 in Thailand and other countries. These results indicate that genetic diversity of PCV2 in Thailand is caused by genetic drift of the local strains and intermittent introduction of new strains or genotypes from other countries. Genetic evolution of PCV2 in Thailand is similar to that occurs globally.

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.

Inactivated chimeric porcine circovirus (PCV) 1-2 vaccines based on genotypes 2b and 2d exhibit similar immunological effectiveness in protecting pigs against challenge with PCV2b strain 0233

Porcine circovirus type 2 (PCV2) is subdivided into four genotypes: PCV2a, PCV2b, PCV2c and PCV2d. Here, for the first time, we compared the efficacy of two experimental inactivated chimeric PCV1-2 vaccines based on genotypes 2b and 2d. Seventeen 3-week-old pigs were divided randomly into four groups. Group 1 and 2 pigs were inoculated with genotype 2b- and 2d-based inactivated vaccines, respectively. At 28 days post-vaccination (DPV), pigs in groups 1-3 were challenged with the PCV2b 0233 strain. All experimental pigs were necropsied at 21 days post-challenge (DPC). Pigs vaccinated with the genotype 2b- or 2d-based vaccine had high antibody titres and lower PCV2b copy numbers in samples of sera, faeces and nasal secretions compared with pigs in the unvaccinated challenge group. Interestingly, we detected no DNA from the challenge strain in the superficial inguinal lymph nodes of the pigs immunized with the PCV2b vaccine, while one pig in the PCV2d- immunized group had detectable DNA from the challenge strain at 21 DPC. We found no significant differences in the humoral immune response, PCV2b load, or PCV-related microscopic lesions between the two vaccinated groups post-challenge. Therefore, both vaccines were equally effective at inducing immunity against challenge with PCV2b strain 0233.