Porcine circovirus type 2 (PCV2) infections: Clinical signs, pathology and laboratory diagnosis

Does porcine circovirus type 3 (PCV3) interfere with porcine circovirus type 2 (PCV2) vaccine efficacy?

PCV2 is globally spread pathogen involved in a number of diseases (PCVD). Commonly used vaccines against PCV2 are proved to be highly efficacious. The role of recently discovered PCV3 for pig health and interference with PCV2 remains unknown. The study performed on serum samples from seven farms vaccinated against PCV2 and four non-vaccinated showed very low prevalence of PCV2 viremia in the former (3 out of 106 positive serum pools) and high prevalence of PCV2 viremia in the latter (35 out of 60 positive pools). Mean log₁₀ PCV2 genome equivalents were lower in vaccinated farms (4.8 ± 0.6 log₁₀  copies/ml) than in non-vaccinated farms (6.3 ± 1.3 log₁₀  copies/ml). PCV3 was detected in 31 out of 106 and 12 out of 60 serum pools from vaccinated and non-vaccinated farms, respectively. Mean log₁₀ PCV3 genome equivalents were significantly (p < 0.05) lower in vaccinated farms (3.9 ± 0.8 log₁₀  copies/ml) than in non-vaccinated farms (4.4 ± 0.6 log₁₀  copies/ml). Concurrent PCV2 and PCV3 infection was rare and found only in 1 out of 529 and 4 out of 292 individual serum samples from vaccinated and non-vaccinated farms, respectively. Our results showed lack of impact of PCV3 circulation on PCV2 vaccine efficacy. On the other hand, intensive PCV2 circulation and high viremia detected in non-vaccinated farms did not seem to increase the level of PCV3 infection.

Porcine Dendritic Cells and Viruses: An Update

Several viral infections of swine are responsible for major economic losses and represent a threat to the swine industry worldwide. New tools are needed to prevent and control endemic, emerging, and re-emerging viral diseases. Dendritic cells (DC) play a central role in linking the innate and adaptive arms of the immune system, so knowledge regarding their interaction with pathogens is necessary to understand the mechanisms underlying diseases pathogenesis and protection. In the first part of this review, we provide an update on the heterogeneous cell subsets that comprise the porcine DC family. In the second part of this review, we provide an overview of how three viruses, affecting pork production at a global level, African swine fever virus (ASFV), classical swine fever virus (CSFV), and porcine circovirus 2 (PCV2), modulate DC function.

Infection dynamics of porcine circovirus type 3 in longitudinally sampled pigs from four Spanish farms

Porcine circovirus type 3 (PCV-3) is a recently discovered virus in domestic pigs and wild boar. The virus has been described in pigs with different clinical/pathological presentations and healthy animals, but the dynamics of infection is currently unknown. The aim of this study was to longitudinally monitor PCV-3 infection in 152 pigs from four different healthy farms (A, B, C and D) by means of PCR in serum. The selected animals were sampled five (farm A) or six (farms B-D) times from weaning until the end of the fattening period. PCV-3 genome was found in pigs from all tested ages and farms; few animals had an apparent long-term infection (4-23 weeks). PCV-3 frequency of detection remained fairly uniform along tested ages within farms A and C, but was more variable among sampling times in farms B and D. Eight partial genome sequences were obtained from six different animals. Phylogenetic tree and pairwise distance analysis showed high similarity among sequences and with available genomes from different countries. This is the first study on PCV-3 infection dynamics in longitudinally sampled pigs. Most pigs got infection during their life, although PCV-3 did not appear to be linked with any specific age.

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.

Human cells are permissive for the productive infection of porcine circovirus type 2 in vitro

Porcine circovirus 2 (PCV2) is the main pathogen of porcine circovirus diseases and porcine circovirus-associated diseases, which are widespread in swine-producing countries. However, there is controversy regarding the susceptibility of human cells to PCV2 infection. In this study, human cell lines were infected with PCV2 and blind passaged several times. PCV2 entered and replicated in human cells, and infectious virions were generated, indicating that human cell lines were permissive to PCV2 replication. Furthermore, PCV2 replication in human cell lines was enhanced by D-glucosamine or concanavalin A (ConA). However, the infection efficiency of PCV2 was lower in human cells than in PK-15 cells, suggesting that PCV2 infection was limited in human cells. Our study reveals that human cells are permissive for the productive infection of porcine circovirus type 2 in vitro.

Phylogenetic analysis of porcine circovirus type 2 in Sardinia, Italy, shows genotype 2d circulation among domestic pigs and wild boars

Porcine circovirus type 2 (PCV2) is associated with multi-factorial syndromes, commonly known as porcine-circovirus-associated diseases, which cause severe economic losses in the swine industry worldwide. Four genotypes (PCV2a, PCV2b, PCV2c, and PCV2d) have been identified. Lately, the prevalence of PCV2d has been increasing in many countries, thereby prefiguring a global replacement of PCV2b. Wild boars are also susceptible to PCV2 infection, with virus prevalence similar to that of domestic pigs. This work was aimed at expanding the knowledge about the molecular epidemiology of PCV2 in Italy. For this purpose, we analysed 40 complete ORF-2 sequences from PCV2 strains isolated from domestic pigs and wild boars in Sardinia (Italy) over a period of 5 years (2009-2013). Phylogenetic and Bayesian analyses were performed on three data sets compiled from DNA sequences over a large geographical area. PCV2b was found to be dominant in Sardinia, whereas no PCV2a and PCV2c were found. This study indicates the presence of genotype PCV2d-2 infecting both domestic and wild pigs, thus confirming its circulation in Italy. Sardinian sequences clustered mostly with Italian isolates and with strains from China, Belgium, Croatia, Taiwan, Korea, and Portugal. Genetic variability of PCV2 in Sardinia appears to be a result of both local viral evolution and different epidemic introduction events.

A broad spectrum monoclonal antibody against porcine circovirus type 2 for antigen and antibody detection

This study described the production, characterization, and application of monoclonal antibodies (mAbs) against porcine circovirus type 2 (PCV2). Twelve stable hybridomas were produced by immunization with purified PCV2a/LG strain and characterized by immunoperoxidase monolayer assay (IPMA), Western blotting, and neutralization assays. All mAbs could react with the PCV2 Cap protein and neutralize PCV2a/LG strain. One of them, mAb 3A5, reacted to all PCV2 strains from PCV2a, PCV2b, and PCV2d and it could be applied to detect PCV2 antigen and antibodies. It was shown that the mAb 3A5 could be used to locate PCV2 antigen in PK15 cells and the inguinal lymph nodes of PCV2b/YJ stain-infected piglets. Furthermore, this mAb could immunoprecipitate the Cap protein in PCV2-infected PK15 cells. Meanwhile, a capture ELISA based on mAb 3A5 was developed and used to specifically test PCV2 antigen from cultures; a linear relationship was observed between the optical density at 405 nm of the ELISA and viral titers (200-12,800 TCID₅₀/mL), with a correlation coefficient of 0.9999. Finally, a competitive ELISA based on mAb 3A5 was developed to specifically detect antibodies in PCV2-infected and immunized pigs, and its sensitivity was higher than that of the blocking ELISA. This study suggested that the mAb 3A5 could be used in several convenient and efficient methods for PCV2 clinical and pathological studies, as well as surveillance in pigs and seroconversion monitoring in the vaccinated pigs.

Efficacy of a novel inactivated Lawsonia intracellularis vaccine in pigs against experimental infection and under field conditions

The efficacy of a novel inactivated Lawsonia intracellularis vaccine, Porcilis® Lawsonia, was compared to that of a commercially available live attenuated vaccine in three experimental vaccination-challenge studies in pigs. The efficacy of the new vaccine was further tested under field conditions on a farm with a history of acute ileitis. The novel inactivated vaccine consists of a freeze-dried antigen fraction that is dissolved just prior to use in either the adjuvant or in Porcilis® PCV M Hyo; an existing combination vaccine against porcine circovirus type 2 and Mycoplasma hyopneumoniae. The three experimental vaccination-challenge trials had a similar design and for each trial 75 piglets were used, randomly allotted to three groups of 25 piglets. The pigs were vaccinated at 4 or 5 weeks of age with either Porcilis® Lawsonia in adjuvant or in associated mixed use with Porcilis® PCV M Hyo (group 1), with the live vaccine (group 2), or left as unvaccinated controls (group 3). The pigs were challenged with virulent Lawsonia intracellularis 3, 4 or 17 weeks after vaccination. Post-challenge the pigs were evaluated for clinical signs, average daily weight gain, shedding and macroscopic as well as microscopic immuno-histological ileum lesion scores. In the field study, the mortality and key performance parameters were evaluated over a period of 8 months. The results of all three experimental vaccination-challenge trials showed that Porcilis® Lawsonia induced statistically significant protection against experimental Lawsonia intracellularis infection. This was demonstrated by lower clinical scores, improved weight gain, reduction of Lawsonia intracellularis shedding and reduction of macroscopic as well as microscopic ileum lesion scores when compared to the controls. The protection induced was superior to that of the commercially available live vaccine. In the field study, Porcilis® Lawsonia proved to be highly efficacious; reducing Lawsonia associated mortality to zero and improving key production parameters.

Genome-wide analysis of long non-coding RNA expression profile in porcine circovirus 2-infected intestinal porcine epithelial cell line by RNA sequencing

Porcine circovirus-associated disease (PCVAD), which is induced by porcine circovirus type 2 (PCV2), is responsible for severe economic losses. Recently, the role of noncoding RNAs, and in particular microRNAs, in PCV2 infection has received great attention. However, the role of long noncoding RNA (lncRNA) in PCV2 infection is unclear. Here, for the first time, we describe the expression profiles of lncRNAs in an intestinal porcine epithelial cell line (IPEC-J2) after PCV2 infection, and analyze the features of differently expressed lncRNAs and their potential target genes. After strict filtering of approximately 150 million reads, we identified 13,520 lncRNAs, including 199 lncRNAs that were differentially expressed in non-infected and PCV2-infected cells. Furthermore, trans analysis found lncRNA-regulated target genes enriched for specific Gene Ontology terms (P < 0.05), such as DNA binding, RNA binding, and transcription factor activity, which are closely associated with PCV2 infection. In addition, we analyzed the predicted target genes of differentially expressed lncRNAs, including SOD2, TNFAIP3, and ARG1, all of which are involved in infectious diseases. Our study identifies many candidate lncRNAs involved in PCV2 infection and provides new insight into the mechanisms underlying the pathogenesis of PCVAD.

Porcine Circovirus 2 Uses a Multitude of Weak Binding Sites To Interact with Heparan Sulfate, and the Interactions Do Not Follow the Symmetry of the Capsid

Porcine circovirus 2 (PCV2) is the smallest pathogenic virus capable of autonomous replication within its host. Infections result in immunosuppression and subsequent death of the host and are initiated via the attachment of the PCV2 icosahedral capsid to heparan sulfate (HS) and chondroitin sulfate B (CSB) glycosaminoglycans on the cell surface. However, the underlying mechanism of structural recognition remains to be explored. Using heparin, a routinely used analog of heparan sulfate, we demonstrate that increasing lengths of heparin exhibit a greater affinity toward PCV2. Our competition assays indicate that dextran sulfate (8 kDa) has a higher affinity for PCV2 than heparin (12 kDa), chondroitin sulfate B (41 kDa), hyaluronic acid (1.6 MDa), and dextran (6 kDa). This suggests that polymers high in sulfate content are capable of competing with the PCV2-heparan sulfate interaction and, thus, have the potential to inhibit PCV2 infection. Finally, we visualized the interaction between heparin and the PCV2 capsid using cryo-electron microscopy single-particle analysis, symmetry expansion, and focused classification. The image reconstructions provide the first example of an asymmetric distribution of heparin on the surface of an icosahedral virus capsid. We demonstrate that each of the 60 capsid subunits that generate the T=1 capsid can bind heparin via one of five binding sites. However, not all of the binding sites were occupied by heparin, and only one-third to two-thirds of the binding sites were occupied. The binding sites are defined by arginine, lysine, and polar amino acids. Mutating the arginine, lysine, and polar amino acids to alanine diminished the binding capacity of PCV2 to heparin.IMPORTANCE It has been demonstrated that porcine circovirus 2 (PCV2) attaches to cells via heparan sulfate (HS) and chondroitin sulfate B (CSB) glycosaminoglycans; however, the underlying structural mechanism describing the HS/CSB recognition by PCV2 remains to be explored. We used cryo-electron microscopy with single-particle analysis, symmetry expansion, and focused classification to visualize the interaction between the PCV2 capsid and heparin, an analog of heparan sulfate, to better than 3.6-Å resolution. We observed that the interaction between PCV2 and heparin does not adhere to the icosahedral symmetry of the capsid. To the best of our knowledge, this is the first example where the interaction between heparin and an icosahedral capsid does not follow the symmetry elements of the capsid. Our findings also suggest that anionic polymers, such as dextran sulfate, may act to inhibit PCV2 infection.

Suppression of lymphocyte apoptosis in spleen by CXCL13 after porcine circovirus type 2 infection and regulatory mechanism of CXCL13 expression in pigs

Porcine circovirus-associated disease (PCVAD) is one of the most serious infectious diseases in pigs worldwide. The primary causative agent of PCVAD is porcine circovirus type 2 (PCV2), which can cause lymphoid depletion and immunosuppression in pigs. Our previous study demonstrated that Laiwu (LW) pigs, a Chinese indigenous pig breed, have stronger resistance to PCV2 infection than Yorkshire × Landrace (YL) pigs. In this study, we found that the YL pigs showed more severe lymphocyte apoptosis and higher viral load in the spleen tissue than LW pigs. To illustrate the differential gene expression between healthy and infected spleens, transcriptome profiling of spleen tissues from PCV2-infected and control YL pigs was compared by RNA sequencing. A total of 90 differentially expressed genes (DEGs) was identified, including CD207, RSAD2, OAS1, OAS2, MX2, ADRB3, CXCL13, CCR1, and ADRA2C, which were significantly enriched in gene ontology (GO) terms related to the defense response to virus and cell-cell signaling, and another nine DEGs, KLF11, HGF, PTGES3, MAP3K11, XDH, CYCS, ACTC1, HSPH1, and RYR2, which were enriched in GO terms related to regulation of cell proliferation or apoptosis. Among these DEGs, the CXCL13 gene, which can suppress lymphocyte apoptosis during PCV2 infection, was significantly down-regulated in response to PCV2 infection in YL but not in LW pigs. By analysis of the regulatory elements in the promoter and 3'-untranslated region (3'-UTR) of porcine CXCL13, we found that the single nucleotide polymorphism (SNP) -1014 G (LW) > A (YL) and the Sus scrofa microRNA-296-5p (ssc-miR-296-5p) participated in regulating CXCL13 expression during the response to PCV2 infection.

Seroprevalence of PCV2 in north eastern hill states of India

This study describe the seroprevalence of porcine circovirus type 2 (PCV2) in north eastern hill (NEH) states of India. Information on PCV2 from NEH states is lacking. Serum samples (306) were collected from the pigs and different epidemiological parameters like age, sex, and litter size of drift or sounder, system of rearing and different clinical symptoms from November 2017 to May 2018. Samples were screened for PCV2 infection by commercially available ELISA kit (INGEZIM PCV IgG and INGEZIM PCV IgM, Ingenasa, Madrid, Spain). Out of 306 serum samples tested, 151 samples were positive for PCV2 infection. An overall PCV2 prevalence of 49.35% was recorded in NEH states of India. Highest prevalence was found in Sikkim (94%) and lowest prevalence in Nagaland (4%). This study revealed that PCV2 is prevalent in all the north eastern states of India which necessitates the need for implementation of prevention and control measures.

Incorporation of ORF2 from Porcine Circovirus Type 2(PCV2) into genetically encoded nanoparticles as a novel vaccine using a self-aggregating peptide

Porcine Circovirus Type 2 (PCV2) is one of the most important pathogens in pigs around the world. PCV2 is a non-enveloped virus and its capsid is formed by a single protein known as open reading frame 2 (ORF2). The aim of this study was to evaluate the antigenicity and immunogenicity of genetically-encoded protein nanoparticles (NPs) containing ORF2 from PCV2 fused to the first 110 amino acids of the N-terminus of polyhedrin from the insect virus Autographa californica nucleopolyhedrovirus (PH(1 -1 1 0)). Our group has previously described that some polyhedrin fragments self-aggregate forming polyhedra-like particles. We identified a self-aggregating signal within the first 110 amino acids from polyhedrin (PH(1 -1 1 0)). Fusing the ORF2 from PCV2 to the carboxyl terminus from PH(1 -1 1 0) results in the formation of NPs which incorporate the antigen of interest. Using this system we synthesized NPs containing PH(1 -1 1 0) fused to ORF2 (PH(1 -1 1 0)PCV2) and purify them to immunize pigs and evaluate the humoral immune response generated by these NPs comparing them to a commercially available vaccine. Pigs immunized with PH(1 -1 1 0)PCV2 NPs produced antibodies against ORF2 from PCV2 as indicated by western blot and ELISA analysis. Antibodies obtained with PH(1 -1 1 0)PCV2 NPs were comparable to those obtained using a commercial PCV2 vaccine. These antibodies neutralized the infection of a recombinant PCV2 expressing the green fluorescent protein (GFP). These results together suggest that the self-aggregating peptide PH(1 -1 1 0) can be used for the synthesis of subunit vaccines against PCV2.

Co-Infection of Swine with Porcine Circovirus Type 2 and Other Swine Viruses

Porcine circovirus 2 (PCV2) is the etiological agent that causes porcine circovirus diseases and porcine circovirus-associated diseases (PCVD/PCVAD), which are present in every major swine-producing country in the world. PCV2 infections may downregulate the host immune system and enhance the infection and replication of other pathogens. However, the exact mechanisms of PCVD/PCVAD are currently unknown. To date, many studies have reported that several cofactors, such as other swine viruses or bacteria, vaccination failure, and stress or crowding, in combination with PCV2, lead to PCVD/PCVAD. Among these cofactors, co-infection of PCV2 with other viruses, such as porcine reproductive and respiratory syndrome virus, porcine parvovirus, swine influenza virus and classical swine fever virus have been widely studied for decades. In this review, we focus on the current state of knowledge regarding swine co-infection with different PCV2 genotypes or strains, as well as with PCV2 and other swine viruses.

Inhibition of Abl or Src tyrosine kinase decreased porcine circovirus type 2 production in PK15 cells

Porcine circovirus type 2 (PCV2) causes huge economic losses in the global swine industry and has a complex and poorly understood virus-host interaction mechanism. We reported that the C-terminal of the capsid protein of all PCV2 isolates shared a strictly conserved PXXP motif that may interact with SH3 domain-containing tyrosine kinases; however, its roles in PCV2 cell entry and replication remain unknown. In this study, we determined that mRNA levels of two SH3 domain-containing tyrosine kinases family (Abl and Src) had distinct profiles (wild-type and PXXP-mutated) during PCV2 infections of PK15 cells. Therefore, we hypothesized that activities of tyrosine kinases (Abl and Fyn) in PK15 cells may be hijacked by PCV2 via its PXXP motif of the Cap, to favor virus replication. Specific inhibitors PP2 of Lck/Fyn and STI-571 of Abl family kinases decreased viral production through suppression of DNA and Cap synthesis at the replication stage. However, based on indirect immunofluorescence assay (IFA), entry of PCV2 virus-like particles (VLPs) into PK15 cells was not altered. Elucidating mechanisms of PCV2-host interactions should provide new insights for development of new compounds to prevent or reduce PCV2 infections.

Co-infection status of classical swine fever virus (CSFV), porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circoviruses (PCV2 and PCV3) in eight regions of China from 2016 to 2018

Classical swine fever virus (CSFV), porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circoviruses (PCV2 and PCV3) are economically important swine viruses that cause reproductive failure and/or respiratory symptoms in pigs. However, the co-infection status of these viruses in Chinese swine herds is not well clarified. In this study, we evaluated the co-infection of these four viruses in 159 pigs collected from 63 herds in eight regions of China from 2016 to 2018. CSFV, PRRSV, PCV2 and PCV3 were detected in 14, 56, 43 and 4 of the pigs, respectively. The percentage of singular infections was 32.71%, while the percentages of dual infections and multiple infections were 15.72% and 3.15%, respectively. The E2 of CSFV, ORF5 of PRRSV, ORF2s of PCV2 and PCV3 from all positive samples were determined and used for phylogenetic analyses. E2-based phylogenetic tree showed that all 14 CSFVs identified in this study belong to 2.1b subtype. ORF5-based phylogenetic tree showed that PRRSV2 is predominant in China while PRRSV1 can also be detected. In addition, 35, 16, 4 and 1 of our PRRSVs are clustered with highly pathogenic PRRSV2, NADC30-like PRRSV2, classical PRRSV2 and PRRSV1, respectively. ORF2-based phylogenetic trees showed that our PCVs are grouped with 2 PCV2 subtypes (PCV2d and PCV2b) and 3 PCV3 subtypes (PCV3a, PCV3b and PCV3c), respectively. Our results provide the latest co-infection status and the diversity of four important swine viruses in Chinese swine herds, which is beneficial for understanding the epidemiology of these viruses.

Characterization of a PCV2d-2 isolate by experimental infection of pigs

Porcine circovirus type 2 (PCV2), a highly prevalent, economically important swine pathogen is classified into different genotypes (PCV2a-f) based on phylogenetic analysis. Since the introduction of extensive vaccination programs, at least two major shifts have been observed in the prevalence of PCV2 genotypes. The first genotype shift from 2a towards 2b occurred around 2003, while in recent years, we are witnessing the second change in genotype prevalence from the predominant 2b towards 2d.In this study, a PCV2d-2 isolate was characterized as a potential challenge virus for the evaluation of PCV2 vaccine efficacy. Ten-week-old pigs carrying low to moderate levels of maternally derived antibodies to PCV2 were infected with the isolate by the nasal route. Over the next 4 weeks post-infection, the pigs were monitored for the presence of viremia, fecal virus excretion, and humoral immune responses. At the end of the post-infection observation period, samples were taken from the mediastinal and mesenteric lymph nodes of the animals and tested for viral load. The gradual depletion of maternally derived antibodies in the sera of piglets was demonstrated by ELISA and virus neutralization tests. Following experimental infection by PCV2d-2, specific IgM antibodies were first detected at 14 days post challenge (dpch), while IgG class antibodies were first detected at 21 dpch. Both viremia and virus shedding could be detected at 7 dpch, in 36 and 50% of the pigs, respectively. The proportion of shedders reached 100% by 14 dpch and remained at this level, while viremia was demonstrated in 86, 100, and 100% of the pigs at 14, 21, and 28 dpch, respectively. Both the mediastinal and mesenteric lymph nodes contained high levels of virus (7.6 and 8.5 log₁₀ copies/mg tissue, respectively).

Development of a droplet digital PCR assay for sensitive detection of porcine circovirus 3

Porcine circovirus 3 (PCV3), a newly emerged circovirus, is associated with porcine dermatitis and nephropathy syndrome, reproductive failure and multi-systemic inflammation disease, and is widely distributed in pig populations worldwide. Therefore, developing specific diagnostic assays will be important for controlling this emerging pathogen. In this study, we developed a novel droplet digital PCR (ddPCR) assay targeting the PCV3 cap gene to improve the sensitivity of PCV3 detection. The established assay is highly specific to PCV3, and does not cross react with other important swine pathogens. The assay's detection limit was 1.68 ± 0.29 copies of PCV3 DNA per reaction (n = 8), an approximately 10-fold greater sensitivity than that of our previously developed quantitative real-time PCR (qPCR) assay for the same virus. The ddPCR assay results were highly reproducible, with intra- and inter-assay coefficient of variation values of <9.0%. Of the 239 archived pig tissue and serum samples, 42 tested positive for PCV3 by the ddPCR assay. Among the 42 positive samples, 31 tested positive by the qPCR assay. Notably, PCV3 was detected in the serum samples collected from commercially imported healthy boars from the US, France and the UK during 2011-2017. The overall agreement between the two assays was 95.39% (228/239). Furthermore, the linear regression analysis showed that the ddPCR and the qPCR results were significantly correlated with an R² value of 0.9945. Collectively, these results indicate that the ddPCR assay is a robust diagnostic tool for sensitive detection of PCV3, even in samples with low viral loads.

Dissecting clinical outcome of porcine circovirus type 2 with in vivo derived transcriptomic signatures of host tissue responses

Background

Porcine Circovirus Type 2 (PCV2) is a pathogen that has the ability to cause often devastating disease manifestations in pig populations with major economic implications. How PCV2 establishes subclinical persistence and why certain individuals progress to lethal lymphoid depletion remain to be elucidated.

Results

Here we present PorSignDB, a gene signature database describing in vivo porcine tissue physiology that we generated from a large compendium of in vivo transcriptional profiles and that we subsequently leveraged for deciphering the distinct physiological states underlying PCV2-affected lymph nodes. This systems genomics approach indicated that subclinical PCV2 infections suppress a myeloid leukocyte mediated immune response. However, in contrast an inflammatory myeloid cell activation is promoted in PCV2 patients with clinical manifestations. Functional genomics further uncovered STAT3 as a druggable PCV2 host factor candidate. Moreover, IL-2 supplementation of primary lymphocytes enabled ex vivo study of PCV2 replication in its target cell, the lymphoblast.

Conclusion

Our systematic dissection of the mechanistic basis of PCV2 reveals that subclinical and clinical PCV2 display two diametrically opposed immunotranscriptomic recalibrations that represent distinct physiological states in vivo, which suggests a paradigm shift in this field. Finally, our PorSignDB signature database is publicly available as a community resource (http://www.vetvirology.ugent.be/PorSignDB/, included in Gene Sets from Community Contributors http://software.broadinstitute.org/gsea/msigdb/contributed_genesets.jsp) and provides systems biologists with a valuable tool for catalyzing studies of human and veterinary disease. Finally, a primary porcine lymphoblast cell culture system paves the way for unraveling the impact of host genetics on PCV2 replication.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5217-5) contains supplementary material, which is available to authorized users.

Detection and genetic characterization of porcine circovirus 3 from aborted fetuses and pigs with respiratory disease in Korea

A novel porcine circovirus 3 (PCV3) was first detected in pigs showing porcine dermatitis and nephropathy syndrome, reproductive failure, and multisystemic inflammation in the USA. Herein, we report on PCV3 as a potential etiological agent of clinical signs, reproductive failure and respiratory distress on Korean pig farms, based on in situ hybridization, pathological, and molecular findings. Confirmation of the presence of PCV3 may increase co-infection with other causative agents of disease in Korean pig herds, indicating the need for further systemic investigation of pathogenicity and of multiple infections with PCV2 genotypes and bacteria, and the development of an effective PCV3 vaccine.

Cross-sectional study on viraemia and shedding of porcine circovirus type 2 in a subclinically infected multiplier sow herd

Vertical and horizontal transmission of porcine circovirus type 2 (PCV2) plays an important role for the spread of PCV2 within piglet-producing farms and following production steps. Further information is crucial to learn about the principles of PCV2 circulation among sows in piglet-producing farms to improve preventive healthcare concerning porcine circovirus diseases (PCVD) in downstream production steps. The present study was conducted as a cross-sectional study in a 400 sow multiplier herd in Germany with no PCV2 vaccination. Blood, faeces and saliva of the sows in all stages of production were tested for PCV2-DNA by real-time PCR. Results were analysed under respect of the parity and stage of production of the sows. PCV2-DNA in faeces or saliva was observed especially in young sows. Highest rates of viraemia in productive sows were found in the early stages of pregnancy. The results revealed that particularly gilts from the quarantine and rearing area and sows up to the second parity play a major role for the spread of PCV2 and thus for the maintenance of PCV2 infection in sow herds. Furthermore, the stage of production had a significant influence on the detection rate of PCV2-DNA in serum, saliva or faeces of the sows.

The importance of on-farm biosecurity: Sero-prevalence and risk factors of bacterial and viral pathogens in smallholder pig systems in Uganda

BACKGROUND

The productivity of pigs in smallholder systems is affected by high disease burden, most of which might not be obvious, with their epidemiology and impact being poorly understood. This study estimated the seroprevalence and identified the risk factors of a range of bacterial and viral pathogens of potential economic and public health importance in domestic pigs in Uganda. A total of 522 clinically healthy pigs were randomly selected from 276 pig farms in Masaka (142) and Lira (134) districts of Uganda in 2015.

RESULTS

Overall the highest animal prevalence was found for Streptococcus suis 73.0% (CI95: 67.0-78.3) in Lira and 68.2% (CI95: 62.7-73.4) in Masaka; followed by Porcine circovirus type 2 with 50.8% (CI95: 44.5-57.2) in Lira and 40.7% (CI95: 35.2-46.5) in Masaka and Actinobacillus pleuro-pneumoniae, 25.6% (CI95: 20.4-31.6) in Lira and 20.5% (CI95: 16.2-25.6) in Masaka. Mycoplasma hyopneumonia prevalence was 20.9% (CI95: 16.2-26.6) in Lira and 10.1% (CI95: 7.1-14.1) in Masaka, while Porcine parvovirus was 6.2% (CI95: 4.0-9.7) in Masaka and 3.4% (CI95: 1.7-6.6) in Lira. Less common pathogens were Influenza A, 8.5% (CI95: 5.6-12.8) in Lira and 2.0% (CI95: 0.9-4.5) in Masaka and Porcine Reproductive and Respiratory Syndrome Virus, 1.7% (CI95: 0.7-4.3) in Lira and 1.3% (CI95: 0.5-3.5) in Masaka. Even less common was Rotavirus A with 0.8% (CI95: 0.2-3.0) in Lira and 0.7% (CI95: 0.2-2.5) in Masaka; the same was for Aujeszky virus with 0.4% (CI95: 0.7-2.4) in Lira and 0.0% (CI95: 0.0-0.1) in Masaka. Co-infection with two pathogens was common and there was a significant association of M. hyo and PCV2 co-occurrence (p = 0.016). Multivariate analysis showed that for S. suis the use of disinfectant reduced odds of sero-positivitey (OR = 0.15; p = 0.017) and pigs less than 6 months were more likely to be infected than older pigs (OR = 3.35; p = 0.047). For M. hyo, crossbred pigs had higher odd of infection compared to local breeds (OR = 1.59; p < 0.001).

CONCLUSIONS

The studied pathogens have high prevalences in smallholder pig production systems and might be silent killers, thus affecting productivity and there is a possibility that some pathogens could spread to humans. Given the limited knowledge of veterinary workers and the poor diagnostic capacities and capabilities in these systems, the diseases are potentially usually under-diagnosed. These findings constitute baseline data to measure the impact of future interventions aiming to reduce disease burden in the pig production systems in Uganda.

Therapeutic Modulation of Virus-Induced Oxidative Stress via the Nrf2-Dependent Antioxidative Pathway

Virus-induced oxidative stress plays a critical role in the viral life cycle as well as the pathogenesis of viral diseases. In response to reactive oxygen species (ROS) generation by a virus, a host cell activates an antioxidative defense system for its own protection. Particularly, a nuclear factor erythroid 2p45-related factor 2 (Nrf2) pathway works in a front-line for cytoprotection and detoxification. Recently, a series of studies suggested that a group of clinically relevant viruses have the capacity for positive and negative regulations of the Nrf2 pathway. This virus-induced modulation of the host antioxidative response turned out to be a crucial determinant for the progression of several viral diseases. In this review, virus-specific examples of positive and negative modulations of the Nrf2 pathway will be summarized first. Then a number of successful genetic and pharmacological manipulations of the Nrf2 pathway for suppression of the viral replication and the pathogenesis-associated oxidative damage will be discussed later. Understanding of the interplay between virus-induced oxidative stress and antioxidative host response will aid in the discovery of potential antiviral supplements for better management of viral diseases.

Histopathological and virological findings in emaciated pigs from Mexico: an exploratory study

The objective of this work was to detect the presence of three main pig respiratory viral agents (porcine rubulavirus [PorPV], porcine circovirus type 2 [PCV-2], and porcine reproductive and respiratory syndrome virus [PRRSV]) in tissues of emaciated piglets from the Baj'o Region (Mexico). Necropsies and histopathological studies of 37 pigs with poor body condition were performed; viruses were detected by molecular biology methods and PCV-2 was further assessed by immunohistochemistry (IHC). Histopathologically, interstitial pneumonia was observed in 25/37 (68%) of the piglets. Also, a varying degree of lymphocyte depletion in lymphoid organs was found in 14/37 (38%) animals. Through polymerase chain reaction (PCR) and/or reverse transcription polymerase chain reaction (RT-PCR), from the 37 pigs, 16 were positive for PCV-2, 18 for PRRSV and 1 for PorPV. In accordance with these results, the infection and/or co-infection with PCV-2 and PRRSV were fairly frequent findings in piglets with poor body condition in Mexico, while the infection by PorPV was apparently negligible. Wasting of post-weaning piglets is a global pig farming problem that causes great economic losses and has been associated with diverse factors: microbial agents, environmental factors, nutritional factors, and management. When the Blue Eye Disease was first reported in Mexico, it was associated with severe wasting in post-weaning piglets. This study demonstrated that this disease does not seem to play such an important role in the wasting as was previously thought.

Breed Differences in PCV2 Uptake and Disintegration in Porcine Monocytes

Porcine circovirus type 2 (PCV2) is associated with various diseases which are designated as PCV2-associated diseases (PCVADs). Their severity varies among breeds. In the diseased pigs, virus is present in monocytes, without replication or full degradation. PCV2 entry and viral outcome in primary porcine monocytes and the role of monocytes in PCV2 genetic susceptibility have not been studied. Here, virus uptake and trafficking were analyzed and compared among purebreds Piétrain, Landrace and Large White and hybrid Piétrain × Topigs20. Viral capsids were rapidly internalized into monocytes, followed by a slow disintegration to a residual level. PCV2 uptake was decreased by chlorpromazine, cytochalasin D and dynasore. The internalized capsids followed the endosomal trafficking pathway, ending up in lysosomes. PCV2 genome was nicked by lysosomal DNase II in vitro, but persisted in monocytes in vivo. Monocytes from purebred Piétrain and the hybrid showed a higher level of PCV2 uptake and disintegration, compared to those from Landrace and Large White. In conclusion, PCV2 entry occurs via clathrin-mediated endocytosis. After entry, viral capsids are partially disintegrated, while viral genomes largely escape from the pathway to avoid degradation. The degree of PCV2 uptake and disintegration differ among pig breeds.

A novel NADC30-like porcine reproductive and respiratory syndrome virus (PRRSV) plays a limited role in the pathogenicity of porcine circoviruses (PCV2 and PCV3) and PRRSV co-infection

Co-infection of porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circoviruses (PCVs) is commonly observed under field conditions and elicits more severe diseases than any singular infection. In this study, the co-infection of PRRSV, PCV2 and PCV3 was analyzed in tissue samples collected from 150 pigs from April 2016 to April 2018. PRRSV, PCV2 and PCV3 was detected in 55 (36.67%), 43 (28.67%) and 3 (2%) of 150 pigs respectively. Remarkably, one lung sample (SD17-36) collected from a diseased pig was co-infected with PRRSV, PCV2 and PCV3. The complete genomes of SD17-36 viruses of PRRSV, PCV2 and PCV3 were determined, which belong to the subgroups of NADC30-like PRRSV, PCV2d and PCV3a respectively. Sequence comparison showed that PRRSV SD17-36 isolate contains a N33 deletion in GP5. Animal challenge study showed that the novel NADC30-like PRRSV SD17-36 isolate is low pathogenic. Our results indicate that the co-infection of PRRSV and PCVs might cause diseases even when PRRSV plays a limited role in the pathogenicity of the co-infection.

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.

Development and validation of a real-time PCR for the detection and quantification of porcine circovirus type 2

Porcine circovirus type 2 (PCV2) is a spherical and non-enveloped virus belonging to the genus Circovirus of the Circoviridae family with a single stranded circular DNA genome. This virus, already detected worldwide, has been associated to several diseases and was implicated as the etiological agent of a disease named postweaning multisystemic wasting syndrome. Several methods have been described for the detection of PCV2, being real-time PCR the most simple and reliable. As far as we know, all the real-time PCR systems described until now are based on ORF2 gene, that exhibit the highest variability. This paper reports the development and validation of a real-time PCR targeted to ORF1 and based on a TaqMan probe for the detection of porcine circovirus type 2 DNA in swine samples. Due to the lack of PCV1 samples, the ability of the test to discriminate between PCV1 and PCV2 positive samples was evaluated in silico. Estimations of 100% specificity and 100% sensitivity were obtained based on the qPCR results with panel of 81 swine samples (known PCV2-positive (n = 50); known PCV2-negative (n = 17); samples positive to other common swine viral pathogens (n = 13) and one sample from a BFDV-positive parrot (n = 1)). Intra- and inter-assay coefficients of variation obtained with three positive samples of different viral charges in five replicates or in five independent assays were below the acceptance threshold. The limit of detection determined with a recombinant plasmid containing the amplicon, led to conclude that this assay can detect at least three plasmid copies.

Porcine Circovirus type 2 - Systemic disease on pig farms and associated knowledge of key players in the pig industry in Central Uganda

Porcine Circovirus type 2 (PCV2) infections and associated diseases have been rarely studied in Africa. There is no report of PCV2 infection-associated morbidity and the level of awareness of stakeholders has never been investigated in Uganda. This cross sectional survey investigated the occurrence of Porcine Circovirus type 2 - systemic disease (PCV2-SD) among pigs and the associated level of awareness of stakeholders in Central Uganda. Data were collected using questionnaires, Focus Group Discussions (FGDs), key informant interviews and laboratory investigations. All respondents (n = 131) and farmers attending FGDs (n = 31) had never heard of PCV2-SD and only 16.7% (n = 2) of the interviewed animal health workers (n = 12) knew about the disease. Among the farms, 20 piglets presenting with a chronic wasting and a persistent diarrhea were detected and sampled for laboratory investigations. Severe lymphoid depletion with histiocytic and macrophage infiltration in lymphoid organs (n = 8), shortening of intestinal villi (n = 9), abscesses in various organs (n = 15) and granulomatous pneumonia (n = 2) were the major histopathological lesions described. Immunohistochemistry and PCR assays on organs with implicating lesions confirmed PCV2 infection in 25% (n = 5) of the 20 pigs. The study confirmed the occurrence of PCV2 infections among piglets with persistent diarrhea on pig farms in central Uganda and revealed a low level of associated knowledge among farmers and veterinary practitioners. The study arouses the need for systematic studies on prevalence of PCV2 infections and sensitization of stakeholders on occurrence of PCV2 infections in Uganda.

The emergence of porcine circovirus 2 infections in the Northeastern part of India: A retrospective study from 2011 to 2017

Porcine circovirus (PCV) infection has emerged as an alarming threat to the pig population of India, especially in the Northeastern region (NER) over the last 10 years. The present study is a comprehensive report of the seroepidemiology of PCV2 and its incidences in the pig population from organized and unorganized farms of the entire NER of India from 2011 to 2017. A total of 5697 serum samples were screened by ELISA and the mean positivity of PCV2 antibodies in suspected sera was 31.27%. A total of 22 confirmed cases of PCV2 infection were recorded during the years 2014-2017. Seroprevalence of PCV2 infection in sows causing reproductive disorders in NER suggested its higher incidence in organized farms (65.7%) as compared to unorganized farms (17.6%). A detailed pathological and histopathological examination of the tissue samples collected from the affected animals indicated the presence of PCV2. Molecular characterization and phylogenetic analysis of four PCV2 isolates depicted the circulation of PCV2d genotype in the states of Meghalaya and Assam.

Fecal Microbiota Transplantation Is Associated With Reduced Morbidity and Mortality in Porcine Circovirus Associated Disease

Porcine circovirus associated disease (PCVAD) is a term used to describe the multi-factorial disease syndromes caused by porcine circovirus type 2 (PCV-2), which can be reproduced in an experimental setting through the co-infection of pigs with PCV-2 and porcine reproductive and respiratory syndrome virus (PRRSV). The resulting PCVAD-affected pigs represent a subpopulation within the co-infected group. In co-infection studies, the presence of increased microbiome diversity is linked to a reduction in clinical signs. In this study, fecal microbiota transplantation (FMT) was investigated as a means to prevent PCVAD in pigs co-infected with PRRSV and PCV-2d. The sources of the FMT material were high-parity sows with a documented history of high health status and robust litter characteristics. The analysis of the donated FMT material showed the absence of common pathogens along with the presence of diverse microbial phyla and families. One group of pigs (n = 10) was administered the FMT while a control group (n = 10) was administered a sterile mock-transplant. Over the 42-day post-infection period, the FMT group showed fewer PCVAD-affected pigs, as evidenced by a significant reduction in morbidity and mortality in transplanted pigs, along with increased antibody levels. Overall, this study provides evidence that FMT decreases the severity of clinical signs following co-infection with PRRSV and PCV-2 by reducing the prevalence of PCVAD.

A Slaughterhouse Survey for Porcine Circovirus Type 2 in Commercial Pigs in Ibadan, Southwest Nigeria

Porcine circovirus type 2 (PCV2) is recognized as one of the most important agents of reproductive disorders in gilts and sows worldwide. It is associated with considerable economic losses in the swine industry due to the unthriftiness, and variable morbidity and mortality it causes in pigs. In spite of the devastation caused by this virus to the global pig industry, there is little or no report of its occurrence in Nigeria. Hence, a slaughterhouse based survey was conducted to determine the prevalence of PCV2 infections in pigs in Ibadan, southwest Nigeria. Using a commercial ELISA kit, 364 pig sera collected from a major abattoir were screened for IgG antibodies against PCV2. The overall prevalence of anti-PCV2 antibodies in the pigs was 1.4 % (5/364), with more female pigs (4/237, 1.7 %) being seropositive than males (1/127, 0.8 %). Since there is no routine vaccination against this swine disease in Nigeria, thus the antibodies detected in the pig sera indicated a natural exposure to the virus. The absence of clinical disease in the pigs also suggests the possibility of a carrier status for these animals and shows that they could serve as hosts for the perpetuation of the disease. These findings underscore the need for continuous surveillance for PCV2 among pigs in Nigeria in order to determine its contribution to production losses incurred in the Nigerian swine industry and aid the development of prevention and control strategies against the disease.

Genomic characterization of circoviruses associated with acute gastroenteritis in minks in northeastern China

Mink circovirus (MiCV), a virus that was newly discovered in 2013, has been associated with enteric disease. However, its etiological role in acute gastroenteritis is unclear, and its genetic characteristics are poorly described. In this study, the role of circoviruses (CVs) in mink acute gastroenteritis was investigated, and the MiCV genome was molecularly characterized through sequence analysis. Detection results demonstrated that MiCV was the only pathogen found in this infection. MiCVs and previously characterized CVs shared genome organizational features, including the presence of (i) a potential stem-loop/nonanucleotide motif that is considered to be the origin of virus DNA replication; (ii) two major inversely arranged open reading frames encoding putative replication-associated proteins (Rep) and a capsid protein; (iii) direct and inverse repeated sequences within the putative 5' region; and (iv) motifs in Rep. Pairwise comparisons showed that the capsid proteins of MiCV shared the highest amino acid sequence identity with those of porcine CV (PCV) 2 (45.4%) and bat CV (BatCV) 1 (45.4%). The amino acid sequence identity levels of Rep shared by MiCV with BatCV 1 (79.7%) and dog CV (dogCV) (54.5%) were broadly similar to those with starling CV (51.1%) and PCVs (46.5%). Phylogenetic analysis indicated that MiCVs were more closely related to mammalian CVs, such as BatCV, PCV, and dogCV, than to other animal CVs. Among mammalian CVs, MiCV and BatCV 1 were the most closely related. This study could contribute to understanding the potential pathogenicity of MiCV and the evolutionary and pathogenic characteristics of mammalian CVs.

Application of Real-Time Quantitative PCR to Detect Mink Circovirus in Naturally and Experimentally Infected Minks

The mink circovirus (MiCV), a newly discovered pathogen, is associated with diarrhea in farmed minks. The prevalence and economic importance of this virus remain poorly understood, and a quantitative method for diagnosis of MiCV infection has not been established. This research aims to develop a highly specific, sensitive, and quantitative assay for MiCV. A Real-Time quantitative polymerase chain reaction (qPCR) assay was developed to detect different isolates of the MiCV in mink samples. The qPCR system is highly sensitive with a detection limit of as low as 10 viral DNA copies. The specificity of this qPCR assay was supported by the absence of cross-reaction with other pathogens. The coefficients of variation were low for both inter-assay and intra-assay variabilities. In addition, the results also expressed the distribution of MiCV in infectious mink tissues with high levels of virus in the skeletal muscle and heart. The heart occupied a higher proportion than other tissues, which can be considered the primary source of test material. This qPCR method could be a useful tool for epidemiological studies and disease management. This method for MiCV is highly specific, sensitive, repeatable, quantitative, and can rapidly determine viral load levels in different tissues samples.

In vitro and in silico studies reveal capsid-mutant Porcine circovirus 2b with novel cytopathogenic and structural characteristics

Porcine circovirus 2 (PCV2) is an icosahedral, non-enveloped, and single-stranded circular DNA virus that belongs to the family Circoviridae, genus Circovirus, and is responsible for a complex of different diseases defined as porcine circovirus diseases (PCVDs). These diseases - including postweaning multisystemic wasting syndrome (PMWS), enteric disease, respiratory disease, porcine dermatitis and nephropathy syndrome (PDNS), and reproductive failure - are responsible for large economic losses in the pig industry. After serial passages in swine testicle (ST) cells of a wild-type virus isolated from an animal with PMWS, we identified three PCV2b viruses with capsid protein (known as Cap protein) cumulative mutations, including two novel mutants. The mutant viruses were introduced into new ST cell cultures for reisolation and showed, in comparison to the wild-type PCV2b, remarkable viral replication efficiency (> 10¹¹ DNA copies/ml) and cell death via necrosis, which were clearly related to the accretion of capsid protein mutations. The analysis of a Cap protein/capsid model showed that the mutated residues were located in solvent-accessible positions on the external PCV2b surface. Additionally, the mutated residues were found in linear epitopes and participated in pockets on the capsid surface, indicating that these residues could also be involved in antibody recognition. Taking into account the likely natural emergence of PCV2b variants, it is possible to consider that the results of this work increase knowledge of Circovirus biology and could help to prevent future serious cases of vaccine failure that could lead to heavy losses to the swine industry.

First-Time Detection of Porcine Reproductive and Respiratory Syndrome Virus and Porcine Circovirus 2 in an Albanian Farrow-to-Finish Herd

The purpose of this case report is to describe for the first time concurrent porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus 2 (PCV-2) infections in a commercial farrow-to-finish pig farm in Albania, as well as the phylogenetical analysis of isolated PRRSV strain. The present study reports on a farrow-to-finish commercial pig farm, located in South Albania. In a percentage of about 40% of weaners in each batch (60-70 piglets per batch), clinical signs, including fever, severe respiratory signs, wasting, jaundice, rough hairy coat, palpable inguinal lymphadenopathy, and high mortality rate, were performed. The clinical signs of sows included sporadic premature farrowings (22%), with increased number of stillbirth (3.3%) and weak piglets (4.1%) based on the record system of the farm. Blood samples were obtained from 8 sows (4 lactating and 4 dry-period sows), 25 piglets of 5 different batches (5 at 15-20 days, 5 at 40 days, 5 at 50 days, 5 of 60 days, and 5 of 70 days), and 5 finishers of 130-150 days of age. Moreover, tissue samples were collected from five weaners at 20-70 days of age. Histopathological examination of lung and lymph node sections revealed findings compatible with PRRSV and PCV-2 infection. Pigs between 15 and 130-140 days of age were positive for type 1 (European) PRRSV and pigs between 50 and 130-140 days of age were positive for PCV-2. Blood serum samples were tested by real-time polymerase chain reaction (PCR) for PCV-2 and one real-time reverse transcription-PCR-positive sample was selected for subsequent complete ORF5 (Gp5) gene sequencing. The results of this case report confirm the detection of PRRSV and PCV-2 concurrent infection in an Albanian farrow-to-finish pig farm. The full-length ORF5 sequence of the detected PRRSV strain (named "Mursi/AL/15") was successfully determined, revealing high nucleotide identity with other type 1 European isolates.

Detection and phylogenetic characterization of porcine circovirus 2 from pigs in Mozambique

Porcine circovirus-associated diseases (PCVADs), caused by porcine circovirus 2 (PCV-2), have a significant economic impact on the swine industry worldwide. In Africa, there is little information, to date, regarding the occurrence of PCV-2, and it has not been reported in Mozambique's swine population. We randomly collected mesenteric lymph nodes ( n = 111) from slaughtered pigs from 9 districts in southern Mozambique. PCV-2 DNA was detected in 54% (62 of 111) of the samples and 78% (23 of 31) of the farms. PCV-2 antigen was detected by immunohistochemistry in lymph nodes (6 of 62; 10%) that were positive for PCV-2 by PCR. Histopathologic changes observed in these lymph nodes were lymphoid depletion, multifocal nodal necrosis, and infiltrates of histiocytes and multinucleate giant cells. One positive sample from each district was selected in order to obtain sequences covering the ORF2 region. Five sequences clustered with PCV-2d, of which 3 sequences from Maputo, Namaacha, and Moamba were grouped with PCV-2d-2; 2 sequences from Manhiça and Matola were grouped as PCV-2d-1; and 4 sequences from Boane, Matutuíne, Chibuto, and Xai-Xai were closely related to PCV-2b-1A/B genotypes. Our study indicates that a diversity of PCV-2 viruses is circulating in the Mozambican swine population.

Immunogenicity evaluation of inactivated virus and purified proteins of porcine circovirus type 2 in mice

Background

Vaccination is considered as an effective and economical way to against PCV2 infection. However, some of commercial available vaccines are based on inactivated viruses, while the others are based on purified protein of PCV2. In the present study, we aimed to compare the immunogenicity of inactivated virus and purified proteins of porcine circovirus type 2 in mice.

Results

The results showed that positive antiserum titers were significantly increased after second, third and fourth immunization using inactivated PCV2 or purified proteins as coating antigen. Moreover, the inactivated PCV2 induced significantly higher levels of PCV2-specific antibodies than that of PCV2 subunit proteins. After PCV2 wild strain challenged, the average daily gain was comparable with that of mice in the mock group, and the sera from both inactivated PCV2-immunized animals and subunit protein Cap+ORF3 + Rep immunized animals had significantly higher neutralizing antibody titers than that of the PBS group. As expected, the neutralizing antibody in the inactivated PCV2 group was significantly higher than that of the subunit protein group. These results indicated that positive antiserum induced by the inactivated PCV2 had a better reactivity and specificity than that of the positive antiserum induced by the purified proteins.

Conclusions

The results in the present study demonstrated inactivated PCV2 is more effective than PCV2 subunit proteins in stimulating immune response to against PCV2 infection.

Exploratory field study on the effect of Porcine circovirus 2 (PCV2) sow vaccination on serological, virological and reproductive parameters in a PCV2 subclinically infected sow herd

Background

This study sought to evaluate the effect of sow vaccination against Porcine circovirus 2 (PCV2) on reproductive parameters during two consecutive reproductive cycles. The study was performed in a PCV2 subclinical infected breeding herd (PCV2 circulation but absence of major reproductive problems). Ninety-four pregnant sows were primo-immunized with a commercial PCV2 vaccine and ninety-seven were injected with phosphate-buffered saline at 6 and 3 weeks before the first studied farrowing, and then boosted at 2 weeks before the second one. Blood samples were taken throughout the study to assess PCV2 DNA load and antibodies. At farrowing, main reproductive parameters and piglet vitality index were registered. In addition, in those litters with more than three mummified or stillborn piglets, microscopic examination and PCV2 antigen detection in foetal myocardium was done.

Results

Vaccinated sows showed significantly higher antibody levels compared to the non-vaccinated counterparts. PCV2 DNA was only detected at farrowing in 2 (4.2%) non-vaccinated sows. Vaccinated sows had 1.3 more live-born piglets per litter at the second cycle than non-vaccinated counterparts. Piglets from vaccinated sows had significantly higher (+ 12.7%) vitality score than the ones born from non-vaccinated sows. No PCV2 compatible lesions neither PCV2 antigen were detected in the tested foetal hearts.

Conclusions

The present study represents a first attempt to demonstrate that PCV2 sow vaccination may have a positive influence on prolificacy and vitality of the offspring in a subclinical infected breeding herd. However, since reproductive outcomes at farm level may be affected by a number of factors, further studies would be needed to confirm this association.

Factors associated with the growing-finishing performances of swine herds: an exploratory study on serological and herd level indicators

Background

Growing and finishing performances of pigs strongly influence farm efficiency and profitability. The performances of the pigs rely on the herd health status and also on several non-infectious factors. Many recommendations for the improvement of the technical performances of a herd are based on the results of studies assessing the effect of one or a limited number of infections or environmental factors. Few studies investigated jointly the influence of both type of factors on swine herd performances. This work aimed at identifying infectious and non-infectious factors associated with the growing and finishing performances of 41 French swine herds.

Results

Two groups of herds were identified using a clustering analysis: a cluster of 24 herds with the highest technical performance values (mean average daily gain = 781.1 g/day +/− 26.3; mean feed conversion ratio = 2.5 kg/kg +/− 0.1; mean mortality rate = 4.1% +/− 0.9; and mean carcass slaughter weight = 121.2 kg +/− 5.2) and a cluster of 17 herds with the lowest performance values (mean average daily gain =715.8 g/day +/− 26.5; mean feed conversion ratio = 2.6 kg/kg +/− 0.1; mean mortality rate = 6.8% +/− 2.0; and mean carcass slaughter weight = 117.7 kg +/− 3.6). Multiple correspondence analysis was used to identify factors associated with the level of technical performance. Infection with the porcine reproductive and respiratory syndrome virus and the porcine circovirus type 2 were infectious factors associated with the cluster having the lowest performance values. This cluster also featured farrow-to-finish type herds, a short interval between successive batches of pigs (≤3 weeks) and mixing of pigs from different batches in the growing or/and finishing steps. Inconsistency between nursery and fattening building management was another factor associated with the low-performance cluster. The odds of a herd showing low growing-finishing performance was significantly increased when infected by PRRS virus in the growing-finishing steps (OR = 8.8, 95% confidence interval [95% CI]: 1.8–41.7) and belonging to a farrow-to-finish type herd (OR = 5.1, 95% CI = 1.1–23.8).

Conclusions

Herd management and viral infections significantly influenced the performance levels of the swine herds included in this study.

Electronic supplementary material

The online version of this article (10.1186/s40813-018-0082-9) contains supplementary material, which is available to authorized users.

Evaluation of the Efficacy and Cross-Protective Immunity of Live-Attenuated Chimeric PCV1-2b Vaccine Against PCV2b and PCV2d Subtype Challenge in Pigs

Porcine circovirus type 2 (PCV2) commercial vaccines are either inactivated PCV2 isolates or subunit vaccine based on the Cap protein of PCV2. Currently, no live-attenuated vaccines are yet available. Although the predominant circulating subtype worldwide is PCV2b, the emerging PCV2d subtype is also increasingly associated with PCV disease. In this study, piglets were inoculated with a live-attenuated chimeric PCV1-2b vaccine before challenged with PCV2b and PCV2d isolates. Thirty-two piglets were randomly divided into seven groups: negative (sham-vaccinated, sham-challenged), VAC+PCV2b (PCV1-2b vaccinated, PCV2b-challenged), VAC+PCV2d (PCV1-2b vaccinated, PCV2d-challenged), CHAL+PCV2b (sham-vaccinated, PCV2b-challenged), CHAL+PCV2d (sham-vaccinated, PCV2d-challenged), CV+PCV2b (commercial-vaccinated, PCV2b-challenged), and CV+PCV2d (commercial-vaccinated, PCV2d-challenged). The results showed that vaccinated challenged groups demonstrated high levels of anti-PCV2 antibody and reduced PCV2b and PCV2d loads both in serum and nasal swabs compared with the challenge-only groups. PCV2 DNA was detected in the superficial inguinal lymph nodes of only one pig in each of the VAC+PCV2b and VAC+PCV2d groups (group mean values, 10^1.81 and 10^1.77 genomic copies/g, respectively), which was significantly lower than those in CHAL+PCV2b and CHAL+PCV2d animals (group mean values, 10^11.65 and 10^10.60 genomic copies/g, respectively; P < 0.01). In addition, PCV2 DNA in each of the VAC+PCV2b and VAC+PCV2d groups was significantly lower than those in CV+PCV2b and CV+PCV2d animals (group mean values, 10^8.47 and 10^8.34 genomic copies/g, respectively; P < 0.01), indicating that the live-attenuated PCV1-2b vaccine was more effective than commercial vaccine. The live-attenuated PCV1-2b vaccine was effective in reducing PCV2b/PCV2d viremia, shedding, and tissue viral loads in vaccinated challenged pigs compared with challenge-only piglets, indicating that the PCV1-2b prototype vaccine is a good candidate for a live-attenuated vaccine against both PCV2b and PCV2d subtypes. And we first revealed that the live-attenuated PCV1-2b vaccine could protect piglets from challenge with either PCV2b or PCV2d equivalently.

Rapid and sensitive detection of mink circovirus by recombinase polymerase amplification

To date, the pathogenic role of mink circovirus (MiCV) remains unclear, and its prevalence and economic importance are unknown. Therefore, a rapid and sensitive molecular diagnosis is necessary for disease management and epidemiological surveillance. However, only PCR methods can identify MiCV infection at present. In this study, we developed a nested PCR and established a novel recombinase polymerase amplification (RPA) assay for MiCV detection. Sensitivity analysis showed that the detection limit of nested PCR and RPA assay was 10¹ copies/reaction, and these methods were more sensitive than conventional PCR, which has a detection limit of 10⁵ copies/reaction. The RPA assay had no cross-reactivity with other related viral pathogens, and amplification was completed in less than 20 min with a simple device. Further assessment of clinical samples showed that the two assays were accurate in identifying positive and negative conventional PCR samples. The detection rate of MiCV by the RPA assay in clinical samples was 38.09%, which was 97% consistent with that by the nested PCR. The developed nested PCR is a highly sensitive tool for practical use, and the RPA assay is a simple, sensitive, and potential alternative method for rapid and accurate MiCV diagnosis.