Isolation and characterisation of circoviruses from pigs with wasting syndromes in Spain, Denmark and Northern Ireland

Genetic and In Vitro Characteristics of a Porcine Circovirus Type 3 Isolate from Northeast China

Porcine circovirus 3 (PCV3) is an emerging virus first discovered in the United States in 2015, and since then, PCV3 has been found in many regions of the world, including America, Asia, and Europe. Although several PCV3 investigations have been carried out, there is a lack of knowledge regarding the pathogenicity of PCV3, mostly due to the limited number of PCV3 isolates that are readily available. In this study, PCV3-DB-1 was isolated in PK-15 cells and characterized in vitro. Electron microscopy revealed the presence of PCV-like particles, and in situ hybridization RNA analysis demonstrated the replication of PCV3 in PK-15 cell culture. Based on phylogenetic analysis of PCV3 isolates from the Heilongjiang province of China, PCV3-DB-1 with 24 alanine and 27 lysine in the Cap protein was originally isolated and determined to belong to the clade PCV3a.

Revisiting Porcine Circovirus Infection: Recent Insights and Its Significance in the Piggery Sector

Porcine circovirus (PCV), a member of the Circoviridae family within the genus Circovirus, poses a significant economic risk to the global swine industry. PCV2, which has nine identified genotypes (a-i), has emerged as the predominant genotype worldwide, particularly PCV2d. PCV2 has been commonly found in both domestic pigs and wild boars, and sporadically in non-porcine animals. The virus spreads among swine populations through horizontal and vertical transmission routes. Despite the availability of commercial vaccines for controlling porcine circovirus infections and associated diseases, the continuous genotypic shifts from a to b, and subsequently from b to d, have maintained PCV2 as a significant pathogen with substantial economic implications. This review aims to provide an updated understanding of the biology, genetic variation, distribution, and preventive strategies concerning porcine circoviruses and their associated diseases in swine.

Production of virus-like particles of porcine circovirus 2 in baculovirus expression system and its application for antibody detection

BACKGROUND

Porcine circovirus 2 (PCV-2) is one of the pathogens that leads to a growing and persistent threat in pigs. Thus, the development of serological detection methods for PCV-2 is of great necessity for clinical diagnosis as well as epidemiological investigations. This study aimed to establish an indirect enzyme-linked immunosorbent assay (ELISA) to examine antibodies against PCV-2 based on virus-like particles (VLPs).

RESULTS

Recombinant PCV-2 Cap protein was expressed in the baculovirus-insect cells system and PCV-2 VLPs were observed over transmission electron microscopy (TEM). The PCV-2 VLPs were shown to have good immunogenicity in mice and stimulated a high level of PCV-2 antibody titers. Using PCV-2 VLPs as coating antigen, the indirect ELISA can detect PCV-2 antibodies in animals with diagnostic sensitivity and specificity of 98.33% and 93.33% compared to immunofluorescence assay (IFA), respectively. The intra- and inter-assay coefficient variations (CVs) were < 10% in a batch, and < 15% in different batches, indicating good repeatability. There was no cross-reaction of this ELISA with antibodies against other porcine viruses. A total of 170 serum samples collected from different pig farms in China were tested for PCV-2 antibodies, and 151 (88.8%) samples were PCV-2 antibody positive.

CONCLUSION

Our findings suggest that this ELISA was rapid, specific, and reproducible and can be used for large-scale serological investigations of PCV-2 antibodies in pigs.

Development of Recombinase Aided Amplification Combined With Disposable Nucleic Acid Test Strip for Rapid Detection of Porcine Circovirus Type 2

Porcine circovirus type 2 (PCV2) is the dominant causative agent of PCV2 systemic disease (PCV2-SD) in pigs. It can also associate with other diseases such as respiratory and enteric diseases, reproductive failure, porcine dermatitis and nephropathy syndrome in pigs. Currently, PCV2 infection is a considerable threat in the swine industry. Therefore, it is of great significance to prevent, control, and accurately detect PCV2 in pig farms. Recombinase aided amplification (RAA) technology is an isothermal nucleic acid amplification technology that could rapidly amplify the target gene fragment at a constant temperature. The amplification products labeled with specific molecules could be visually detected using the test strip with the corresponding antibody. In the present study, the RAA technology combined with a nucleic acid test strip (RAA-strip) was established for simple and specific detection of PCV2. Primers and probes targeting the PCV2 ORF2 gene were designed according to the RAA technology principles. The PCV2 RAA-strip established in this study could detect as low as 10³ copies/μL of recombinant plasmids containing the PCV2 ORF2 gene fragment. The lowest detection limit about viral DNA and virus titers was 6.7 × 10^-6 ng/μL and 10 TCID50/mL, respectively. Furthermore, no cross-reaction with other porcine viruses occurred at 37°C and within 15 min. We used 42 clinical samples to assess the performance of our established method. The positive rate of clinical samples detected by PCV2 RAA-strip was 50.00%. This was similar to that detected by PCV2 PCR (45.24%). In conclusion, due to the advantages of strong specificity, high sensitivity, excellent reproducibility, and simple operation method, our PCV2 RAA-strip is suitable for the rapid clinical detection of PCV2 on-site.

Pathogenic Characterization of a Porcine Circovirus Type 3 Isolate from Heilongjiang, China

The clinical outcome of porcine circovirus 3 (PCV3) infection is still controversial. Herein, a novel PCV3 isolate (PCV3-China/DB-1/2017) with the molecular characterization of 24A and 27K in the Cap protein was used to inoculate three-week-old cesarean-derived, colostrum-deprived piglets. The nine PCV3 DB-1 inoculated piglets exhibited no obvious clinical symptoms or macroscopic lesions. PCV3 displayed a broad histotropism, including the heart, liver, spleen, lung, kidney, brain, lymph nodes, and tonsil, and the lungs and lymph nodes contained a higher quantity of viral genomes compared to that of the other organs. From 7 days after PCV3 DB-1 inoculation, the piglets showed obvious IgG antibody responses against PCV3 rCap-VLPs. The cumulative results demonstrated that PCV3 trend to low pathogenicity.

A nanobody-horseradish peroxidase fusion protein-based competitive ELISA for rapid detection of antibodies against porcine circovirus type 2

Background

The widespread popularity of porcine circovirus type 2(PCV2) has seriously affected the healthy development of the pig industry and caused huge economic losses worldwide. A rapid and reliable method is required for epidemiological investigation and evaluating the effect of immunization. However, the current methods for PCV2 antibody detection are time-consuming or very expensive and rarely meet the requirements for clinical application. we have constructed the platform for expressing the nanobody(Nb)‑horseradish peroxidase(HRP) fusion protein as an ultrasensitive probe to detect antibodies against the Newcastle disease virus(NDV), previously. In the present work, an Nb-HRP fusion protein-based competitive ELISA(cELISA) for rapid and simple detection antibodies against PCV2 was developed using this platform to detect anti-PCV2 antibodies in clinical porcine serum.

Results

Using phage display technology, 19 anti-PCV2-Cap protein nanobodies were screened from a PCV2-Cap protein immunized Bactrian camel. With the platform, the PCV2-Nb15‑HRP fusion protein was then produced and used as a sensitive reagent for developing a cELISA to detect anti‑PCV2 antibodies. The cut‑off value of the cELISA is 20.72 %. Three hundreds and sixty porcine serum samples were tested by both newly developed cELISA and commercial kits. The sensitivity and specificity were 99.68 % and 95.92 %, respectively. The coincidence rate of the two methods was 99.17 %. When detecting 620 clinical porcine serum samples, a good consistent (kappa value = 0.954) was found between the results of the cELISA and those of commercial kits.

Conclusions

In brief, the newly developed cELISA based PCV2-Nb15‑HRP fusion protein is a rapid, low-cost, reliable and useful nanobody-based tool for the serological evaluation of current PCV2 vaccine efficacy and the indirect diagnosis of PCV2 infection.

Construction of polycistronic baculovirus surface display vectors to express the PCV2 Cap(d41) protein and analysis of its immunogenicity in mice and swine

To increase expression levels of the PCV2 Cap(d41) protein, novel baculovirus surface display vectors with multiple expression cassettes were constructed to create recombinant baculoviruses BacSC-Cap(d41), BacDD-2Cap(d41), BacDD-3Cap(d41), and BacDD-4Cap(d41). Our results reveal that the recombinant baculovirus BacDD-4Cap(d41) was able to express the highest levels of Cap(d41) protein. Optimum conditions for expressing the PCV2 Cap(d41) protein were determined, and our results show that 107 of Sf-9 infected with the recombinant baculovirus BacDD-4Cap(d41) at an MOI of 5 for 3 days showed the highest level of protein expression. Mice immunized with the 4Cap(d41) vaccine which was prepared from the recombinant baculovirus-infected cells (107) elicited higher ELISA titers compared to the Cap (d41) vaccine. The 4Cap(d41) vaccine could elicit anti-PCV2 neutralizing antibodies and IFN-γ in mice, as confirmed by virus neutralization test and IFN-γ ELISA. Moreover, the swine lymphocyte proliferative responses indicated that the 4Cap(d41) vaccine was able to induce a clear cellular immune response. Flow cytometry analysis showed that the percentage of CD4+ T cells and CD4+/CD8+ ratio was increased significantly in SPF pigs immunized with the 4Cap(d41) vaccine. Importantly, the 4Cap(d41) vaccine induced an IFN-γ response, further confirming that its effect is through cellular immunity in SPF pigs. An in vivo challenge study revealed that the 4Cap(d41) and the commercial vaccine groups significantly reduce the viral load of vaccinated pigs as compared with the CE negative control group. Taken together, we have successfully developed a 4Cap(d41) vaccine that may be a potential subunit vaccine for preventing the disease associated with PCV2 infections.

Reservoirs of Porcine Circoviruses: A Mini Review

Porcine circovirus (PCV) is one of the smallest known DNA viruses in mammals. At present, PCVs are divided into three species, PCV1, PCV2, and PCV3. PCV1 and PCV2 were found in the 1970s and the 1990s, respectively, whereas PCV3 was discovered recently in 2016. PCV1 does not cause diseases in pigs. However, PCV3, similar to PCV2, is reported to be associated with several swine diseases, including porcine dermatitis and nephropathy syndrome (PDNS) and reproductive failure. PCVs are very common in domestic pigs as well as wild boars. However, PCVs have been occasionally isolated from non-porcine animals, including ruminants (such as cattle, goats, wild chamois, and roe deers), rodents (such as NMRI mice, BALB/c mice, Black C57 mice, ICR mice, Mus musculus, and Rattus rattus), canines (such as dogs, minks, foxes, and raccoon dogs), insects (such as flies, mosquitoes, and ticks), and shellfish. Moreover, PCVs are frequently reported in biological products, including human vaccines, animal vaccines, porcine-derived commercial pepsin products, and many cell lines. PCVs are also abundant in the environment, including water samples and air samples. Interestingly, PCV1 and/or PCV2 antibody or antigen has also been detected in sera, stool samples and respiratory swab samples of human, revealing zoonotic potential of PCVs. Thus, PCVs inhabit many types of reservoirs. In this review, we summarize the reservoirs of PCVs, and this information would be helpful in understanding the natural circulating status and possible cross-species transmission of PCVs.

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.

Molecular detection and phylogenetic analysis of porcine circovirus type 3 in 21 Provinces of China during 2015-2017

The emerging Porcine circovirus type 3 (PCV3) is associated with porcine dermatitis and nephropathy syndrome, reproductive failure and cardiac and multisystemic inflammation. To trace the prevalence and evolution of PCV3 in pigs with respiratory diseases or digestive diseases in China, 616 samples were collected from 21 provinces or municipalities of China from 2015 to 2017. All samples were analysed with PCR and a cap-gene-based phylogeny. The results indicated that the positive rate of PCV3 was 12.2% (75/616) at the sample level; 24.1% (42/174) at the farm level; 10.4% (50/480) in the digestive-disease-affected samples; 26.6% (25/94) in the respiratory-disease-affected samples; all 42 healthy samples were negative for PCV3. A statistical analysis showed that PCV3 infection was closely associated with both digestive diseases (p < 0.05) and respiratory diseases (p < 0.01). A sequence analysis revealed that the cap genes of the 51 PCV3 strains identified in our study shared nucleotide homologies of 97.2%-100% and amino acid homologies of 96.3%-100%. A total of 17 amino acid mutations were observed among the Cap proteins of the 51 PCV3 strains, of which R¹⁰ /K, A²⁴ /V, R²⁷ /K, T⁷⁷ /S, F¹⁰⁴ /Y, I¹⁵⁰ /L are mutations among worldwide strains. A phylogenetic analysis demonstrated that the 51 PCV3 strains formed three clades, including PCV3a (15/51, 29.4%), PCV3b (21/51, 41.2%) and PCV3c (15/51, 29.4%). These data provide evidence that PCV3 exhibits high prevalence and genetic diversity and is associated with digestive diseases and respiratory diseases in pig.

Eukaryotic Circular Rep-Encoding Single-Stranded DNA (CRESS DNA) Viruses: Ubiquitous Viruses With Small Genomes and a Diverse Host Range

While single-stranded DNA (ssDNA) was once thought to be a relatively rare genomic architecture for viruses, modern metagenomics sequencing has revealed circular ssDNA viruses in most environments and in association with diverse hosts. In particular, circular ssDNA viruses encoding a homologous replication-associated protein (Rep) have been identified in the majority of eukaryotic supergroups, generating interest in the ecological effects and evolutionary history of circular Rep-encoding ssDNA viruses (CRESS DNA) viruses. This review surveys the explosion of sequence diversity and expansion of eukaryotic CRESS DNA taxonomic groups over the last decade, highlights similarities between the well-studied geminiviruses and circoviruses with newly identified groups known only through their genome sequences, discusses the ecology and evolution of eukaryotic CRESS DNA viruses, and speculates on future research horizons.

Immunogenicity of Pigeon Circovirus Recombinant Capsid Protein in Pigeons

Pigeon circovirus (PiCV) is the most frequently diagnosed virus in pigeons and is thought to be one of the causative factors of a complex disease called the young pigeon disease syndrome (YPDS). The development of a vaccine against this virus could be a strategy for YPDS control. Since laboratory culture of PiCV is impossible, its recombinant capsid protein (rCP) can be considered as a potential antigen candidate in sub-unit vaccines. The aim of this basic research was to evaluate the immune response of pigeons to PiCV rCP. Sixty six-week-old carrier pigeons were divided into two groups (experimental immunized with PiCV rCP mixed with an adjuvant, and control immunized with an adjuvant only), and immunized twice in a 21-day interval. On the day of immunization and on two, 23, 39, and 46 days post first immunization (dpv), samples of blood, spleen, and bursa of Fabricius were collected from six birds from each group to examine anti-PiCV rCP IgY, anti-PiCV rCP IgY-secreting B cells (SBC), IFN-γ gene expression, and percentage of T CD3⁺, CD4⁺, CD8⁺, and B IgM⁺ lymphocytes. The results indicated a correct immune response to PiCV rCP both in humoral and cell-mediated immunity, which was manifested by seroconversion since 23 dpv, by a significantly higher anti-PiCV rCP IgY-SBC number on two and 23 dpv, and significantly higher IFN-γ gene expression since two dpv. There were no significant differences or trends noted between particular T and B lymphocyte subpopulations. To conclude, PiCV rCP may be deemed immunogenic and could be considered as an antigen candidate in sub-unit vaccines against PiCV infections in pigeons.

Regulation of Apoptosis During Porcine Circovirus Type 2 Infection

Apoptosis, an indispensable innate immune mechanism, regulates cellular homeostasis by removing unnecessary or damaged cells. It contains three signaling pathways: the mitochondria-mediated pathway, the death receptor pathway and the endoplasmic reticulum pathway. The importance of apoptosis in host defenses is stressed by the observation that multiple viruses have evolved various strategies to inhibit apoptosis, thereby blunting the host immune responses and promoting viral propagation. Porcine Circovirus type 2 (PCV2) utilizes various strategies to induce or inhibit programmed cell death. In this article, we review the latest research progress of the apoptosis mechanisms during infection with PCV2, including several proteins of PCV2 regulate apoptosis via interacting with host proteins and multiple signaling pathways involved in PCV2-induced apoptosis, which provides scientific basis for the pathogenesis and prevention of PCV2.

Global Status of Porcine circovirus Type 2 and Its Associated Diseases in Sub-Saharan Africa

Globally, Porcine circovirus type 2 (PCV2) is a recognized viral pathogen of great economic value in pig farming. It is the major cause of ravaging postweaning multisystemic wasting syndrome (PMWS) and many other disease syndromes generally regarded as Porcine circovirus associated diseases (PCVAD) in Europe. PCV2 infections, specifically PMWS, had impacted huge economic loss on swine production at different regions of the world. It has been studied and reported at different parts of the globe including: North and South America, Europe, Asia, Oceania, Middle East, and the Caribbean. However, till date, this virus and its associated diseases have been grossly understudied in sub-Sahara African region and the entire continent at large. Two out of forty-nine, representing just about 4% of countries that make up sub-Sahara Africa presently, have limited records on reported cases and occurrence of the viral pathogen despite the ubiquitous nature of the virus. This review presents an overview of the discovery of Porcine circovirus and its associated diseases in global pig herds and emphasizes the latest trends in PCV2 vaccines and antiviral drugs development and the information gaps that exist on the occurrence of this important viral pathogen in swine herds of sub-Saharan Africa countries. This will serve as wake-up call for immediate and relevant actions by stakeholders in the region.

A double-antibody sandwich ELISA based on the porcine circovirus type 2 (PCV2) propagated in cell culture for antibody detection

ABSTRACT: Few studies have described enzyme-linked immunosorbent assays (ELISAs) for the detection of antibodies against porcine circovirus type 2 (PCV2) based on antigens produced in cell culture. Furthermore, few articles have described viral purification techniques for members of the family Circoviridae. This occurs because circoviruses are difficult to isolate, noncytopathogenic, and produce low viral titres in cell culture. Thus, for overcoming these difficulties in the cultivation of PCV2, this study aimed to develop a double-antibody sandwich ELISA based on the cell culture antigen PCV2b for the quantification of anti-PCV2 antibodies. A 20% and 50% discontinuous sucrose cushion was used for viral purification, which enabled the separation of cell culture proteins in the 20% sucrose cushion and a greater viral concentration in the 50% sucrose cushion. Following isopycnic centrifugation, PCV2 was concentrated in the band with density values from 1.330 to 1.395g/cm3. Viral purification was assessed using SDS-PAGE, indirect ELISA and electron microscopy. The standardised ELISA revealed a strong linear correlation (r= 0.826, p<0.001) when compared with a commercial ELISA kit. The assay exhibited low variability (inter-assay coefficient of variation of 4.24% and intra-assay of 1.80%) and excellent analytical specificity conferred by the capture antibody produced in rabbit. Thus, this ELISA is a rapid, specific and convenient method for the detection of antibodies against PCV2 in studies of experimental and natural infection, and in monitoring the response to vaccination on commercial farms.

Immunogenicity of porcine circovirus type 2 nucleic acid vaccine containing CpG motif for mice

BACKGROUND

This study aimed at reseaching the immune effect of porcine circovirus type 2 (PCV2) DNA vaccine containing CpG motif on mice.

METHODS

A total of 40 6-week-old female BALB/c mice were randomly divided into four groups which were immunized by 18CpG-pVAX1-ORF2, pVAX1-ORF2, pVAX1 and PBS, respectively, and immunized again 2 weeks later. All mice were challenged with 0.2 mL PCV2 cells virulent strain SD (106.0 TCID50/mL) after 4 weeks. Average daily gain, blood antibody levels, microscopic changes and viremia were detected to estimate the effect of DNA vaccine.

RESULTS AND DISCUSSION

The results showed that compared to those of the control mice, groups immunized with pVAX1-ORF2 and 18CpG-pVAX1-ORF2 could induce PCV2-specific antibodies. The PCV2-specific antibodies level of 18 CpG-pVAX1-ORF2 groups was higher significantly than other groups and decreased slowly along with time. There was no distinct pathological damage and viremia occurring in mice that inoculated with CpG motif DNA vaccines. The results demonstrated that the DNA vaccine containing 18 CpG could build up resistibility immunity and reduce immune organ damage on mice.

Reproduction of Postweaning Multisystemic Wasting Syndrome in Pigs Experimentally Inoculated with a Swedish Porcine Circovirus 2 Isolate

In recent years, porcine circovirus type 2 (PCV2)—associated postweaning multisystemic wasting syndrome (PMWS) has been reported worldwide. However, to date, PMWS has not been reported in Sweden despite the demonstration of serum antibodies to a PCV2-like virus in Swedish pigs. This communication reports the experimental reproduction of clinical PMWS after inoculation of colostrum-deprived (CD) pigs, derived from a Northern Ireland herd, with an isolate of PCV2 virus recovered from a clinically normal Swedish pig that was necropsied in 1993. The clinical disease and histological lesions observed in CD pigs inoculated with this virus were indistinguishable from those observed in previous studies on CD pigs inoculated with a PCV2 virus isolate recovered from pigs with PMWS. These results highlight the disease potential of PCV2 isolated from regions apparently free of PMWS and suggest that the status of the host and its environment is an important factor in the development of clinical PMWS.

Porcine circovirus type 2 protective epitope densely carried by chimeric papaya ringspot virus-like particles expressed in Escherichia coli as a cost-effective vaccine manufacture alternative

Porcine circovirus type 2 (PCV2) still represents a major problem to the swine industry worldwide, causing high mortality rates in infected animals. Virus-like particles (VLPs) have gained attention for vaccine development, serving both as scaffolds for epitope expression and immune response enhancers. The commercial subunit vaccines against PCV2 consist of VLPs formed by the self-assembly of PCV2 capsid protein (CP) expressed in the baculovirus vector system. In this work, a PCV2 protective epitope was inserted into three different regions of papaya ringspot virus (PRSV) CP, namely, the N- and C-termini and a predicted antigenic region located near the N-terminus. Wild-type and chimeric CPs were modeled in silico, expressed in Escherichia coli, purified, and visualized by transmission electron microscopy. This is the first report that shows the formation of chimeric VLPs using PRSV as epitope-presentation scaffold. Moreover, it was found that PCV2 epitope localization strongly influences VLP length. Also, the estimated yields of the chimeric VLPs at a small-scale level ranged between 65 and 80 mg/L of culture medium. Finally, the three chimeric VLPs induced high levels of immunoglobulin G against the PCV2 epitope in immunized BALB/c mice, suggesting that these chimeric VLPs can be used for swine immunoprophylaxis against PCV2.

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

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

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

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

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Application protected pigs from subsequent PCV2b challenge.

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Vaccination reduced pro-inflammatory but increased antiviral cytokine expression.

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

Improvement of the Immunogenicity of Porcine Circovirus Type 2 DNA Vaccine by Recombinant ORF2 Gene and CpG Motifs

Nowadays, adjuvant is still important for boosting immunity and improving resistance in animals. In order to boost the immunity of porcine circovirus type 2 (PCV2) DNA vaccine, CpG motifs were inserted. In this study, the dose-effect was studied, and the immunity of PCV2 DNA vaccines by recombinant open reading frame 2 (ORF2) gene and CpG motifs was evaluated. Three-week-old Changbai piglets were inoculated intramuscularly with 200 μg, 400 μg, and 800 μg DNA vaccines containing 14 and 18 CpG motifs, respectively. Average gain and rectum temperature were recorded everyday during the experiments. Blood was collected from the piglets after vaccination to detect the changes of specific antibodies, interleukin-2, and immune cells every week. Tissues were collected for histopathology and polymerase chain reaction. The results indicated that compared to those of the control piglets, all concentrations of two DNA vaccines could induce PCV2-specific antibodies. A cellular immunity test showed that PCV2-specific lymphocytes proliferated the number of TH, TC, and CD3+ positive T-cells raised in the blood of DNA vaccine immune groups. There was no distinct pathological damage and viremia occurring in pigs that were inoculated with DNA vaccines, but there was some minor pathological damage in the control group. The results demonstrated that CpG motifs as an adjuvant could boost the humoral and cellular immunity of pigs to PCV2, especially in terms of cellular immunity. Comparing two DNA vaccines that were constructed, the one containing 18 CpG motifs was more effective. This is the first report that CpG motifs as an adjuvant insert to the PCV2 DNA vaccine could boost immunity.

Biology and Diseases of Swine

Swine are used in biomedical research as models for biomedical research and for teaching. This chapter covers normative biology and behavior along with common and emerging swine diseases. Xenotransplantation is discussed along with similarities and differences of swine immunology.

High prevalence of co-infection with multiple Torque teno sus virus species in Italian pig herds

Torque teno viruses (TTVs) are a large group of vertebrate-infecting small viruses with circular single-stranded DNA, classified in the Anelloviridae family. In swine, two genetically distinct species, Torque teno sus virus 1a (TTSuV1a) and 1b (TTSuV1b) are currently grouped into the genus Iotatorquevirus. More recently, a novel Torque teno sus virus species, named Torque teno sus virus k2b (TTSuVk2b), has been included with Torque teno sus virus k2a (TTSuVk2a) into the genus Kappatorquevirus. In the present study, TTSuV1 (TTSuV1a and TTSuV1b), TTSuVk2a and TTSuVk2b prevalence was evaluated in 721 serum samples of healthy pigs from Sardinian farms, insular Italy. This is the largest study to date on the presence of TTSuV in healthy pigs in Italy. The global prevalence of infection was 83.2% (600/721), being 62.3% (449/721), 60.6% (437/721), and 11.5% (83/721) the prevalence of TTSuV1, TTSuVk2a and TTSuVk2b, respectively. The rate of co-infection with two and/or three species was also calculated, and data show that co-infections were significantly more frequent than infections with single species, and that TTSuV1+TTSuVk2a double infection was the prevalent combination (35.4%). Quantitative results obtained using species-specific real time-qPCR evidenced the highest mean levels of viremia in the TTSuV1 subgroup, and the lowest in the TTSuVk2b subgroup. Interestingly, multiple infections with distinct TTSuV species seemed to significantly affect the DNA load and specifically, data highlighted that double infection with TTSuVk2a increased the viral titers of TTSuV1, likewise the co-infection with TTSuVk2b increased the titers of TTSuVk2a.

Porcine circovirus-2 capsid protein induces cell death in PK15 cells

Studies have shown that Porcine circovirus (PCV)-2 induces apoptosis in PK15 cells. Here we report that cell death is induced in PCV2b-infected PK15 cells that express Capsid (Cap) protein and this effect is enhanced in interferon gamma (IFN-γ)-treated cells. We further show that transient PCV2a and 2b-Cap protein expression induces cell death in PK15 cells at rate similar to PCV2 infection, regardless of Cap protein localization. These data suggest that Cap protein may have the capacity to trigger different signaling pathways involved in cell death. Although further investigation is needed to gain deeper insights into the nature of the pathways involved in Cap-induced cell death, this study provides evidence that PCV2-induced cell death in kidney epithelial PK15 cells can be mapped to the Cap protein and establishes the need for future research regarding the role of Cap-induced cell death in PCV2 pathogenesis.

Interaction of porcine circovirus type 2 replication with intracellular redox status in vitro

OBJECTIVES

Redox status influences replication of some viruses but its effect on porcine circovirus type 2 (PCV2), the primary causative agent of the emerging swine disease post-weaning multisystemic wasting syndrome is not known. The interaction of PCV2 replication with intracellular redox status in PK15 cells was examined in this study.

METHODS

Intracellular glutathione (GSH) was measured spectrophotometrically by reaction with 5, 5'-dithiobis (2-nitrobenzoic acid). Total superoxide dismutase activity (SOD) was assayed by inhibition of oxyamine oxidation by the xanthine oxidase system. Malondialdehyde (MDA) was assayed spectrophotometrically using the thiobarbituric acid reaction. Both quantification of PCV2 DNA by real-time polymerase chain reaction and indirect immunofluorescence of PCV2-infected cells were used to evaluate the replication of PCV2.

RESULTS

Both GSH and SOD decreased significantly at 48 hours after PCV2 infection, whereas MDA concentration increased significantly after 48 hour post-infection. Furthermore, PCV2 replication in PK15 cells was significantly impaired after the elevation of intracellular GSH through treatment with the antioxidant N-acetyl-l-cysteine (NAC), a precursor in GSH synthesis. In contrast, PCV2 replication in PK15 cells was enhanced after reduction of GSH levels through H2O2-mediated oxidation. In addition, NAC treatment blocked the increase of virus replication induced by H2O2.

CONCLUSIONS

This study suggests that PCV2 infection induces oxidative stress and that intracellular redox status influences PCV2 replication in PK15 cells.

Experimental airborne transmission of porcine postweaning multisystemic wasting syndrome

The objective of these studies was to investigate if porcine postweaning multisystemic wasting syndrome (PMWS) could be induced in healthy pigs following contact with air from pigs with clinical signs of PMWS. The pigs were housed in different units. Either 31 (study I) or 25 (study II) pigs with clinical symptoms of PMWS from a PMWS-affected herd and 25 healthy pigs from a PMWS-free, but PCV2-positive, herd were housed in unit A. Fifty pigs from a PMWS-free herd were housed in unit B, which were connected by pipes to unit A. In unit C, 30 pigs from a PMWS-free herd were housed as controls. In study II, the pigs in units A and B from the PMWS-free herd developed clinical signs of PMWS 2-3 weeks after arrival. PMWS was confirmed at necropsy and the diseased pigs had increased PCV2 load and increased antibody titers against PCV2 in serum that coincided with the development of clinical signs typical of PMWS. Sequence analysis revealed that the PCV2 isolate belonged to genotype 2b. In conclusion, the present study showed that PMWS can be induced in pigs from a PMWS-free herd by airborne contact with pigs from a PMWS-affected herd.

Identification and functional analysis of the novel ORF4 protein encoded by porcine circovirus type 2

Porcine circovirus type 2 (PCV2) is the primary causative agent of porcine circovirus-associated diseases in pigs. To date, viral proteins Cap, Rep, Rep', and ORF3, encoded by the PCV2 genome, have been described. Here, transcription and translation of a novel viral gene within the PCV2 genome (designated ORF4) was determined and functionally analyzed in vitro and in vivo. Northern blot analysis indicated that the RNA transcribed from the ORF4 gene is about 180 bp in length and overlaps ORF3 in the same direction. Site-directed mutagenesis confirmed that the viral ORF4 protein is not essential for virus replication in PK-15 cells and in mice infected with an ORF4-deficient PCV2 (PCV2Δ). PCV2Δ triggered higher activity levels of caspase-3 and -8 than wild-type PCV2 (wPCV2) in PK-15 cells. The antigenic epitopes of two mouse monoclonal antibodies (MAbs) raised against the viral ORF4 protein were mapped to the same 19KSSASPR25 peptide. Expression of ORF4 was confirmed using the specific MAbs in wPCV2-infected PK-15 cells and mice. Mice infected with PCV2Δ had a higher serum viral load (genomic copies) and more severe lymphoid tissue damage in the spleen than those infected with wPCV2. Meanwhile, flow-cytometric analysis indicated that the PCV2Δ infection caused a significant decrease of CD4(+) and CD8(+) T lymphocytes. Our results demonstrate that ORF4 is a newly discovered viral protein that is not essential for PCV2 replication but plays a role in suppressing caspase activity and regulating CD4(+) and CD8(+) T lymphocytes during PCV2 infection.

Analysis of putative ORF3 gene within porcine circovirus type 2

Porcine circovirus type 2 (PCV2) is associated with postweaning multisystemic syndrome in pigs, whereas the ubiquitous related porcine circovirus type 1 (PCV1) is nonpathogenic. Corroborating an earlier observation in PCV2, Rep and Rep' proteins encoded by ORF1 are essential for the initiation of PCV2 replication. Cap protein encoded by ORF2 has a potential causative role in the initiation of PCV2 replication and contains a type-specific epitope. The putative ORF3 of PCV2 oriented in the opposite direction within ORF1 is unknown. In this study, ORF3-encoding protein of PCV2 was expressed in vitro as a fusion protein (GST-ORF3 protein), and monoclonal antibodies (MAbs) to the PCV2-ORF3-encoding protein were generated and biologically characterized. The mRNA transcript of ORF3 was characterized during a productive infection in PK-15 cells, and the PCV2 infectious DNA clone lacking ORF3 was constructed. GST-ORF3 protein, with an approximate molecular weight of 37.7 kDa, was obtained from the Escherichia coli transformed with the recombinant vector pGEX-4T-1-F3 after codon optimization of ORF3 DNA sequence. Four MAbs reacted strongly to the ORF3-encoding protein expressed in PK-15 cells in immunohistochemical staining. The mRNA transcript of ORF3 was confirmed in RT-PCR, Northern blot, and sequencing analyses. The progeny PCV2 virions were not revealed in the PK-15 cells transfected by the PCV2 infectious DNA clone without ORF3. These results demonstrate that the ORF3 of PCV2 can be transcribed and expressed and that ORF3-encoding protein plays a pivotal role in viral replication.

Circoviruses: immunosuppressive threats to avian species: a review

Circoviruses are small, non-enveloped, icosahedral viruses that are unique among animal viruses in having circular, single-stranded DNA genomes. Their genomes are also the smallest possessed by animal viruses. The circovirus family currently comprises three members, chicken anaemia virus, porcine circovirus, and psittacine beak and feather disease virus, with pigeon circovirus being classified as a tentative member. Infections with each of the four circoviruses are associated with potentially fatal diseases in which virus-induced damage to lymphoid tissue and immunosuppression are common features. Experience with other animal virus families suggests that additional animal species will be infected by, as yet undiscovered, circoviruses and that these may display similar tissue tropism and disease-causing potential. Recent reports describing the association of circovirus-like viruses with immunodeficiency-related diseases of geese and southern black-backed gulls suggest that circovirus infections of avian species may be more common than previously recognized, and prompt the question of whether novel circoviruses infect poultry to cause clinical and/or subclinical diseases that may be economically important. This review has three purposes. First, it is designed to summarize the currently available information about the classified circoviruses and viruses that are regarded as circovirus-like. Second, it aims to alert the readership to the possibility that other avian species, including commercial poultry, may be infected with novel circoviruses. Finally, possible methods for discovering novel circoviruses and for controlling infections by such viruses are suggested.

An indirect enzyme-linked immunosorbent assay using a recombinant truncated capsid protein of Porcine circovirus-2

Porcine circovirus-2 (PCV-2) serology is commonly used for PCV-2 herd status determination and optimal timing of PCV-2 vaccination programs. The objectives of the current study were to develop an in-house indirect enzyme-linked immunosorbent assay (ELISA) using a recombinant nuclear localization signal truncated capsid (rntCap) protein expressed in an Escherichia coli system and to determine the diagnostic performance of the developed rntCap indirect ELISA in comparison with immunoperoxidase monolayer assays (IPMAs). Based on a receiver operating characteristic (ROC) curve analysis of the rntCap indirect ELISA ( n = 90), an optimum cutoff optical density (OD) of 0.330 was determined, which resulted in diagnostic sensitivity, diagnostic specificity, and accuracy of 98.33%, 93.33%, and 96.67%, respectively. Average OD values of the positive ( n = 8) and negative sera ( n = 8) tested by either purified glutathione-S-transferase (GST) protein or the rntCap protein as the coating antigen revealed that the mean OD values tested by the rntCap indirect ELISA were significantly different from using GST alone ( P < 0.005). The correlation between the established rntCap indirect ELISA and the IPMA results demonstrated as the linear regression (Spearman correlation coefficient = 0.772, P < 0.005) indicated that the OD ratio obtained from the rntCap indirect ELISA could be used to predict the levels of the IPMA titers. More samples are needed for enhancing the diagnostic sensitivity, specificity and accuracy. In conclusion, the establishment of the rntCap indirect ELISA could be used as a serodiagnostic assay for large-scale detection of PCV-2 antibodies in swine and has the capability to be produced commercially for routine use in diagnostic laboratories.

An experimental live chimeric porcine circovirus 1-2a vaccine decreases porcine circovirus 2b viremia when administered intramuscularly or orally in a porcine circovirus 2b and porcine reproductive and respiratory syndrome virus dual-challenge model

Commercially available inactivated vaccines against porcine circovirus type 2 (PCV2) have been shown to be effective in reducing PCV2 viremia. Live-attenuated, orally administered vaccines are widely used in the swine industry for several pathogens because of their ease of use yet they are not currently available for PCV2 and efficacy. The aims of this study were to determine the efficacy of a live-attenuated chimeric PCV2 vaccine in a dual-challenge model using PCV2b and porcine reproductive and respiratory syndrome virus (PRRSV) and to compare intramuscular (IM) and oral (PO) routes of vaccination. Eighty-three 2-week-old pigs were randomized into 12 treatment groups: four vaccinated IM, four vaccinated PO and four non-vaccinated (control) groups. Vaccination was performed at 3 weeks of age using a PCV1-2a live-attenuated vaccine followed by no challenge, or challenge with PCV2b, PRRSV or a combination of PCV2b and PRRSV at 7 weeks of age. IM administration of the vaccine elicited an anti-PCV2 antibody response between 14 and 28 days post vaccination, 21/28 of the pigs being seropositive prior to challenge. In contrast, the anti-PCV2 antibody response in PO vaccinated pigs was delayed, only 1/27 of the pigs being seropositive at challenge. At 21 days post challenge, PCV2 DNA loads were reduced by 80.4% in the IM vaccinated groups and by 29.6% in the PO vaccinated groups. PCV1-2a (vaccine) viremia was not identified in any of the pigs. Under the conditions of this study, the live attenuated PCV1-2a vaccine was safe and provided immune protection resulting in reduction of viremia. The IM route provided the most effective protection.

Emerging and re-emerging swine viruses

In the past two decades or so, a number of viruses have emerged in the global swine population. Some, such as porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV2), cause economically important diseases in pigs, whereas others such as porcine torque teno virus (TTV), now known as Torque teno sus virus (TTSuV), porcine bocavirus (PBoV) and related novel parvoviruses, porcine kobuvirus, porcine toroviruses (PToV) and porcine lymphotropic herpesviruses (PLHV), are mostly subclinical in swine herds. Although some emerging swine viruses such as swine hepatitis E virus (swine HEV), porcine endogenous retrovirus (PERV) and porcine sapovirus (porcine SaV) may have a limited clinical implication in swine health, they do pose a potential public health concern in humans due to zoonotic (swine HEV) or potential zoonotic (porcine SaV) and xenozoonotic (PERV, PLHV) risks. Other emerging viruses such as Nipah virus, Bungowannah virus and Menangle virus not only cause diseases in pigs but some also pose important zoonotic threat to humans. This article focuses on emerging and re-emerging swine viruses that have a limited or uncertain clinical and economic impact on pig health. The transmission, epidemiology and pathogenic potential of these viruses are discussed. In addition, the two economically important emerging viruses, PRRSV and PCV2, are also briefly discussed to identify important knowledge gaps.

Porcine circovirus-associated disease in weaner pigs in Western Australia

OBJECTIVE

To report the occurrence and pathology of porcine circovirus type 2 (PCV2)-associated disease (PCVAD) of postweaning pigs in two Australian pig herds.

METHODS

Mortality data from two commercial piggeries that experienced higher than normal postweaning illthrift and mortalities were examined. Gross and histopathological examinations were performed on the index cases, and at weekly intervals thereafter for a period of 10 weeks. Specimens were submitted to the laboratory for routine diagnostic testing and for exclusion of porcine reproductive and respiratory syndrome virus (PRRSV). The genomes of two strains of PCV2 isolated during testing were sequenced.

RESULTS

Mortality rates in weaned, 5-12-week-old pigs spiked significantly during mid to late 2007. This increase in the mortalities was mainly attributed to salmonella-associated diarrhoea and illthrift. Salmonellosis was diagnosed in 73/110 cases inclusive of both piggeries. Many pigs also had chronic granulomatous lymphadenitis and diffuse histiocytic interstitial pneumonia consistent with PCVAD and associated with varying amounts of PCV2 antigen and inclusion bodies. All samples tested for PRRSV were negative. Sequence analysis of the PCV2 isolates showed strain differences between piggeries.

CONCLUSION

This report describes the first outbreaks of PCVAD in growing pigs in Western Australia (WA) and describes lesions not previously seen in this laboratory. It also describes the first isolation of a PCV2 group 1 virus in WA associated with PCVAD. Although the outbreaks of PCVAD occurred with concurrent salmonellosis, the two diseases were unrelated. Neither of the outbreaks met the Australian case definition for the diagnosis of postweaning multisystemic wasting syndrome.

Genetic characterization of porcine circovirus type 2 in piglets from PMWS-affected and -negative farms in Thailand

Porcine circovirus type 2 (PCV2) is the major swine pathogen associated with Porcine circovirus associated disease (PCVAD) including post-weaning multisystemic wasting syndrome (PMWS). Currently, there are 4 subtypes of PCV2 (PCV2a, b, c and d) and some epidemiological evidences demonstrated that virulence of PCV2 may relate to its subtypes. Recently, PMWS was observed more frequently in swine farms in Thailand; however, the information regarding to PCV2 subtype involved was limited. Therefore, this study was aimed to determine the association between occurrence of PMWS and PCV2 subtypes as well as genetically characterize PCV2 in Thailand. PCV2 DNA was isolated from faecal swabs and whole blood of piglets from PMWS-affected and -negative farms. The full length ORF2 sequences were compared using multiple alignment. The results showed that PCV2 DNA was detected more frequently in PMWS-affected farms. The nucleotide identities of the ORF2 from 9 PCV2 isolates representing each PMWS-affected farm and one from the negative farm ranged from 92.4 to 99.5% suggesting that there is some genetic variation of PCV2 in Thai swine. The 10 PCV2 isolates were classified into 2 clusters, in which the 7 isolates from PMWS-positive farms were in PCV2b cluster 1 A/B. The remaining isolates were separated in the new subtype called PCV2e. The results suggest the presence of new PCV2 subtypes in addition to PCV2a and PCV2b in Asian swine population. However, correlation between subtypes and virulence of PCV2 infection is not conclusive due to limited number of the PCV2 sequences from PMWS negative farms.

Rapid detection of porcine circovirus type 2 using a TaqMan-based real-time PCR

Porcine circovirus type 2 (PCV2) and the associated disease postweaning multisystemic wasting syndrome (PMWS) have caused heavy losses in global agriculture in recent decades. Rapid detection of PCV2 is very important for the effective prophylaxis and treatment of PMWS. To establish a sensitive, specific assay for the detection and quantitation of PCV2, we designed and synthesized specific primers and a probe in the open reading frame 2. The assay had a wide dynamic range with excellent linearity and reliable reproducibility, and detected between 10² and 10¹⁰ copies of the genomic DNA per reaction. The coefficient of variation for Ct values varied from 0.59% to 1.05% in the same assay and from 1.9% to 4.2% in 10 different assays. The assay did not cross-react with porcine circovirus type 1, porcine reproductive and respiratory, porcine epidemic diarrhea, transmissible gastroenteritis of pigs and rotavirus. The limits of detection and quantitation were 10 and 100 copies, respectively. Using the established real-time PCR system, 39 of the 40 samples we tested were detected as positive.

One dose of a porcine circovirus 2 subunit vaccine induces humoral and cell-mediated immunity and protects against porcine circovirus-associated disease under field conditions

This study investigated the efficacy of a one-dose porcine circovirus 2 (PCV2) subunit vaccine based on the PCV2 Cap protein expressed in a baculovirus system on two different farms at which a history of porcine circovirus-associated disease (PCVD) was present. Morbidity, mortality, average daily weight gain, carcass weight, PCV2 load in serum and vaccine immunogenicity were assessed. Serology to porcine reproductive and respiratory syndrome virus (PRRSV) and Mycoplasma hyopneumoniae was performed. A double-blind, randomised, and controlled field trial was performed distributing 818 piglets between two treatment groups. At inclusion (weaning at 21 ± 3 days of age), 408 animals (group B) received a 2-mL intramuscular dose of Porcilis PCV(®) (vaccinated group). Controls (group A, 410 pigs) received 2 mL of the adjuvant Diluvac Forte(®) intramuscularly. Weights were recorded at inclusion and at 12 and 26 weeks of age, and the average daily weight gain (ADWG) was calculated. The carcass weights of the pigs from farm 2 were recorded at slaughter (274 days old). All dead animals (died or culled) underwent autopsy to classify them as PMWS-affected or not. At each farm, blood samples were taken from 22 pigs/group for serologic studies. A beneficial effect was found after vaccination with a single dose of a PCV2 Cap vaccine against PCVD. The vaccination reduced the mortality rate and morbidity, reduced PCV2 viremia and viral load, improved productive performances (e.g. ADWG: +70 g/day between 12 and 26 weeks of age when viremia and the specific disease occurred) as well as carcass weight at slaughter age (+4.5 kg). These effects were associated with virologic and clinical protection from the immunogenicity of the vaccine measured as activation of both a humoral and a cellular immune response.

Distribution of porcine circovirus 2 cap antigen in the lymphoid tissue of pigs affected by postweaning multisystemic wasting syndrome

The lymphatic organs of 50 pigs from a total of eight farms located at different sites in the epizootiological region of North Bačka County were studied to obtain data on the prevalence of circoviral infections in Serbia. All of the pigs examined had clinical signs suggestive of postweaning multisystemic wasting syndrome (PMWS). All pigs underwent necropsy and tissue samples were taken for histopathological, immunohistochemical (IHC) and PCR analysis. The presence of porcine circovirus 2 (PCV2) was established by PCR analysis in the organs of the pigs tested. The most frequent histopathological lesions of lymphoid tissue linked with the presence of positive immunostaining for PCV2 Cap antigen confirmed the existence of PMWS in all farms tested in North Bačka County. Using PCR, histopathological and IHC techniques, the presence of PMWS was proved in the Republic of Serbia. During necropsy, generalised enlargement of the lymph nodes was evident. The most common histopathological finding was lymphocyte depletion in the follicular and perifollicular areas of lymph nodes. Infiltration by macrophages was also recorded. By IHC analysis, the cytoplasm of macrophages was shown to contain a large amount of the ORF2-coded Cap antigen of PCV2. Lymphocyte depletion and large numbers of macrophages were recorded in the tonsils, spleen, intestinal lymphatic tissue, Peyer's patches and ileocaecal valve. The presence of typical granulomatous lesions with multinuclear giant cells (MGCs) was also recorded in the lymphatic tissue. Cap antigen was shown to be present in macrophages and less often in lymphocytes.

Epidemiology and horizontal transmission of porcine circovirus type 2 (PCV2)

Porcine circovirus type 2 (PCV2) is a small, non-enveloped, circular, single-stranded DNA virus of economic importance in the swine industry worldwide. Based on the sequence analyses of PCV2 strains, isolates can be divided into five subtypes (PCV2a–e). PCV2 is an ubiquitous virus based on serological and viremia data from countries worldwide. In addition, PCV2 DNA was discovered in archived samples prior to the first recognition of clinical disease. Recently, a worldwide shift in PCV2 subtype from PCV2a to PCV2b occurred. PCV2 DNA can be detected in fecal, nasal, oral and tonsillar swabs as well as in urine and feces from both naturally and experimentally infected pigs. PCV2 DNA can be detected early in the infectious process and persists for extended periods of time. The effectiveness of disinfectants for reducing PCV2in vitrois variable and PCV2 is very stable in the pig environment. Limited data exist on the horizontal transmission of PCV2. Direct transmission of PCV2 between experimentally or naturally infected animals and naïve animals has been documented and the incorporation of clinical or subclinically infected animals into a population represents a risk to the herd. Indirect transmission through the oral, aerosol or vaccine routes is likely a lesser risk for the transmission of PCV2 in most swine populations but may be worth evaluating in high heath herds. The objective of this review was to discuss data on the epidemiology and horizontal transmission of PCV2.