In vitro and in vivo characterization of an infectious clone of a European strain of porcine circovirus type 2

PDZK1 upregulates nitric oxide production through the PI3K/ERK2 pathway to inhibit porcine circovirus type 2 replication

Porcine circovirus type 2 (PCV2) is the causative agent of porcine circovirus-associated disease. Changes in host cell gene expression are induced by PCV2 infection. Here, we showed that porcine PDZ Domain-Containing 1 (PDZK1) expression was enhanced during PCV2 infection and that overexpression of PDZK1 inhibited the expression of PCV2 Cap protein. PCV2 genomic DNA copy number and viral titers were decreased in PDZK1-overexpressing PK-15B6 cells. PDZK1 knockdown enhanced the replication of PCV2. Overexpression of PDZK1 activated the phosphoinositide 3-kinase (PI3K)/ERK2 signaling pathway to enhance nitric oxide (NO) levels, while PDZK1 knockdown had the opposite effects. A PI3K inhibitor (LY294002) and a NO synthase inhibitor (L-NAME hydrochloride) decreased the activity of PDZK1 in restricting PCV2 replication. ERK2 knockdown enhanced the proliferation of PCV2 by decreasing levels of NO. Levels of interleukin (IL)- 4 mRNA were reduced in PDZK1 knockdown and ERK2 knockdown PK-15B6 cells. Increased IL-4 mRNA levels were unable to decrease NO production in PDZK1-overexpressing cells. Thus, we conclude that PDZK1 affected PCV2 replication by regulating NO production via PI3K/ERK2 signaling. PDZK1 affected IL-4 expression through the PI3K/ERK2 pathway, but PDZK1 modulation of PCV2 replication occurred independently of IL-4. Our results contribute to understanding the biological functions of PDZK1 and provide a theoretical basis for the pathogenic mechanisms of PCV2.

Renal Tubular Necrosis and Interstitial Hemorrhage (“Turkey-Egg Kidney”) in a Circovirus-Infected Yorkshire Cross Pig

A juvenile Yorkshire cross pig with rapidly progressive acute renal failure was submitted for necropsy. There was marked edema and disseminated petechiation of both kidneys, producing the “turkey-egg” appearance that is characteristic of exotic diseases such as African and classical swine fever. Microscopic findings included renal tubular epithelial necrosis with extensive interstitial edema and hemorrhage; lymphoplasmacytic, eosinophilic, and histiocytic tubulointerstitial nephritis; and numerous botryoid intracytoplasmic inclusions within the renal tubular epithelium and interstitial macrophages. Porcine circovirus 2 (PCV2) was readily identified within these lesions by both PCV2-specific immunohistochemistical staining and electron microscopy. Tests for African and classical swine fever viruses, as well as bacterial cultures, were negative. The striking renal lesions in this pig were attributed to PCV2 infection and are distinct from those that are typical of other PCV2-associated diseases.

Efficacy of single dose of an inactivated porcine circovirus type 2 (PCV2) whole-virus vaccine with oil adjuvant in piglets

Background

Post-weaning multisystemic wasting syndrome (PMWS) associated with PCV2 is one of the most costly diseases currently faced by the swine industry. The development of effective vaccines against PCV2 infection has been accepted as an important strategy in the prophylaxis of PMWS.

Methods

In the present study, a PK-15 cell-adapted formalin-inactivated prototype vaccine candidate was prepared using a strain of PCV2 from China. Inactivation of the virus was accomplished using a standard formalin inactivation protocol. The protective properties of the inactivated PCV2 vaccine were evaluated in piglets. Ten 28-day-old pigs were randomly assigned to two groups, each with five. Group 1 was vaccinated intramuscularly with the inactivated virus preparation; Group 2 received sterile PBS as a placebo. By 28 days post-vaccination (DPV), Groups 1 and 2 were challenged intranasally and intramuscularly with 5 × 10⁷ TCID₅₀ of a virulent PCV2 isolate.

Results

The vaccinated pigs seroconverted to PCV2 and had high levels of serum antibodies to PCV2 at 28 days after vaccination, whereas the control pigs remained seronegative. No significant signs of clinical disease were recorded following the challenge with PCV2, but moderate amounts of PCV2 antigen were detected in most lymphoid organs of the control pigs. PCV2 was detected in two out of the five vaccinated pigs. Furthermore, pathological lesions and viremia were milder in the vaccinated group.

Conclusions

The obtained results indicate that the inactivated PCV2 virus vaccine with an oil adjuvant induce an immunological response in pigs that appears to provide protection from infection with PCV2. The vaccine, therefore, may have the potential to serve as a vaccine aimed to protect pigs from developing PMWS.

A novel porcine circovirus-like agent P1 is associated with wasting syndromes in pigs

A novel porcine pathogen tentatively named P1, which was obtained from the sera of the pigs exhibiting clinical signs of postweaning multisystemic wasting syndrome (PMWS) experimentally caused the classical clinic signs and pathologic lesions of the disease in pigs by direct in vivo injection with P1 DNA plasmids. Twenty colostrum-fed (CF) pigs that were free of PCV2 and P1 at 1 month of age were randomly designated equally to two groups. Group 1 pigs were each injected with 400 µg of the cloned P1 plasmid DNA into the superficial inguinal lymph nodes and Group 2 were injected with same amount of the empty pSK vector DNA and served as controls. Viremias were positively detected in 8 of 10 P1 infected pigs from 14–21 days post-inoculation (dpi). The 8 infected animals showed pallor of skin and diarrhea. Gross lesions in the pigs euthanized on 35 dpi were similarly characterized by encephalemia, haemorrhage of the bladder mucosa, haemorrhage of the superficial inguinal lymph nodes, lung atrophy and haemorrhage. Histopathological lesions were arteriectasis and telangiectasia of the cavitas subarachnoidealis, interstitial pneumonia, mild atrophy of the cardiac muscle cells, histiocytic hyperplasia of the follicles in the tonsils, and haemorrhage of the inguinal lymph nodes. P1 DNA and antigens were confirmed by PCR and immunohistochemistry in the tissues and organs of the infected pigs, including the pancreas, bladders, testicles/ovaries, brains, lungs and liver. There were no obvious clinical signs and pathological lesions in the control pigs. This study demonstrated that P1 infection is one of the important pathologic agents on pig farms.

Naked PCV-2 cloned genomic DNA is infectious by mucosal (intratracheal or oro-nasal) inoculation

Porcine circovirus type 2 (PCV-2) is involved in several diseases named porcine circovirus-associated diseases and is transmitted by oro-faecal route. In this study we inoculated porcine-circovirus free piglets by mucosal routes (intratracheal or oro-nasal routes) with a plasmid carrying two copies of PCV-2 genomic DNA and compared the results to the intramuscular route. We observed that this PCV-2 naked DNA serves as template for viral replication and infectious PCV-2 particles are detected in the whole body after parenteral (intramuscular) or mucosal (intratracheal or oro-nasal) delivery. These results suggest that PCV-2 genome could play a role in in vivo transmission.

Functional exchangeability of the nuclear localization signal (NLS) of capsid protein between PCV1 and PCV2 in vitro: Implications for the role of NLS in viral replication

BACKGROUND

Porcine circovirus type 2 (PCV2) is believed to be the primary causative agent of postweaning multisystemic wasting syndrome (PMWS). It is supposed that capsid protein of PCV may contribute to replication control via interaction between Cap and Rep in the nucleoplasm. In this study, we described the construction and in vitro characterization of NLS-exchanged PCV DNA clones based on a PMWS-associated PCV2b isolate from China to determine the role of ORF2 NLS in PCV replication.

RESULTS

The PCV1, PCV2, PCV2-NLS1 and PCV1-NLS2 DNA clone were generated by ligating a copy of respective genome in tandem with a partial duplication. The PCV2-NLS1 and PCV1-NLS2 DNA clone contained a chimeric genome in which the ORF2 NLS was exchanged. The four DNA clones were all confirmed to be infectious in vitro when transfected into PK-15 cells, as PCV capsid protein were expressed in approximately 10-20% of the transfected cells. The in vitro growth characteristics of the DNA clones were then determined and compared. All the recovered progeny viruses gave rise to increasing infectious titers during passages and were genetically stable by genomic sequencing. The chimeric PCV1-NLS2 and PCV2-NLS1 viruses had the final titers of about 104.2 and 103.8 TCID50/ml, which were significantly lower than that of PCV1 and PCV2 (105.6 and 105.0 TCID50/ml, respectively). When the ORF2 NLS exchanged, the mutant PCV2 (PCV2-NLS1) still replicated less efficiently and showed lower infectious titer than did PCV1 mutant (PCV1-NLS2), which was consistent with the distinction between wild type PCV1 and PCV2.

CONCLUSIONS

Recovery of the chimeiric PCV1-NLS2 and PCV2-NLS1 progeny viruses indicate that the nuclear localization signal sequence of capsid protein are functionally exchangeable between PCV1 and PCV2 with respect to the role of nuclear importing and propagation. The findings also reveal that ORF2 NLS play an accessory role in the replication of PCV. However, we found that ORF2 NLS was not responsible for the distinction of in vitro growth characteristic between PCV1 and PCV2. Further studies are required to determine the in vivo viral replication and pathogenicity of the NLS chimeric DNA clones.

The open reading frame 3 (ORF3) of porcine circovirus type 2 (PCV2) is dispensable for virus infection but evidence of reduced pathogenicity is limited in pigs infected by an ORF3-null PCV2 mutant

Porcine circovirus type 2 (PCV2) is the primary causative agent of porcine circovirus-associated diseases (PCVAD) in pigs. The open reading frame (ORF) 3 of PCV2 reportedly induces apoptosis and is associated with PCV2 pathogenicity. In this study, we first created an ORF3-null PCV2 mutant (muPCV2) by site-directed mutagenesis and demonstrated that the dimerized plasmid DNA of muPCV2 clone is infectious when injected intramuscularly (I.M.) into pigs. Subsequently, by using a well-characterized pig model we compared the pathogenicity of the muPCV2 and the wildtype PCV2. Thirty-one pigs were divided into 3 groups of 11, 10, and 10 each: group 1 pigs were each inoculated I.M. with PBS buffer as negative controls, group 2 pigs each with 200 microg of muPCV2 infectious DNA clone, and group 3 pigs each with 200 microg of wildtype PCV2 infectious DNA clone. Blood was collected prior to inoculation and weekly thereafter, and tested for PCV2 antibodies by ELISA and serum viral DNA loads by quantitative PCR. All pigs were necropsied at 35 days post-inoculation. The results showed that pigs inoculated with muPCV2 had a delayed seroconversion and lower serum viral load. However, there was no significant difference in the average scores of the histological or gross lesions or the amount of PCV2-specific antigen in tissues between wildtype PCV2- and muPCV2-inoculated groups. Thus, the data from this study do not fully support the conclusion of a previous report regarding PCV2 attenuation by abrogation of ORF3 although the results did show that ORF3 is dispensable for PCV2 replication in pigs.

Swine torque teno virus detection in pig commercial vaccines, enzymes for laboratory use and human drugs containing components of porcine origin

Torque teno viruses (TTVs) are vertebrate infecting, single-stranded circular DNA viruses. Two genetically distinct TTV genogroups (TTV1 and TTV2) infect swine worldwide with high prevalence. Currently, swine TTVs are considered non-pathogenic, although TTV2 has been linked to post-weaning multisystemic wasting syndrome, a porcine circovirus disease. On the other hand, pig materials are an important source of components used in porcine vaccine manufacturing, human drugs and commercial enzyme products. However, there is little information about the possible existence of extraneous viruses in products containing porcine-derived components. In the present study, 26 commercial swine vaccines, seven human drugs and three enzyme products from porcine origin were tested for the presence of TTV1 and TTV2 genomes by PCR. Four vaccines against Mycoplasma hyopneumoniae were positive for TTV2 by PCR. Three M. hyopneumoniae, one porcine parvovirus and one porcine reproductive and respiratory syndrome virus vaccines were PCR positive for TTV1. One human drug contained TTV1 DNA as well as a trypsin enzyme; a porcine-derived elastase product was positive for both TTV genogroups. These results show that swine TTVs are contaminants not only of swine vaccines but also of human drugs containing porcine components and enzymes for laboratory use.

A meta-analysis on experimental infections with porcine circovirus type 2 (PCV2)

A meta-analysis was performed with the aim to identify factors with a relevant influence on the expression of clinical postweaning multisystemic wasting syndrome (PMWS) under experimental conditions. Data from 44 studies were included in the analysis. Several variables were studied: number of pigs in the experiment, intake of colostrum, serological status against porcine circovirus type 2 (PCV2), strain of PCV2 used for inoculation, the route and dose of inoculation, and use of potential triggering factors (such as co-infections, vaccinations, or immunomodulator products). Multiple correspondence analysis and log-linear regression methods were used to establish the relationships between the studied variables and the number of PCV2 infected pigs that developed PMWS. Based on the results of the meta-analysis, the most successful animal experiment aimed to develop PMWS should include: (1) colostrum-deprived pigs, (2) age of inoculation below 3 weeks, (3) high doses of PCV2 inoculum, (4) PCV2 strain from genotype 1, and (5) co-infection with another swine pathogen as a triggering factor.

Immunogenicity of porcine circovirus type 2 capsid protein targeting to different subcellular compartments

Porcine circovirus type 2 (PCV2) is known to be associated with post-weaning multisystemic wasting syndrome (PMWS), an emerging disease in swine. The development of effective vaccines against PCV2 infection has been accepted as an important strategy in the prophylaxis of PMWS, and a DNA vaccine expressing the major immunogenic capsid (Cap) protein of PCV2 is considered to be a promising candidate. However, recent studies have revealed that interferons (IFNs), especially IFN-gamma, can enhance the replication of PCV2, indicating that the high levels of IFN-gamma induced by DNA vaccination seem to have potential deleterious effect on protective immunity. Strategies to improve the neutralizing antibody response and simultaneously decrease the IFN-gamma response will facilitate the clinical application of DNA vaccines against PCV2. In the present study, four different DNA vaccine constructs encoding cytoplasmic (Cy-ORF2), secreted (Sc-ORF2), membrane-anchored (M-ORF2) or authentic nuclear-targeted (pc-ORF2) Cap protein were generated to evaluate the neutralizing antibody and IFN-gamma responses in a mouse model. Although all four DNA constructs could elicit PCV2-specific humoral immune responses, mice inoculated with Sc-ORF2 developed a significantly higher level of neutralizing antibodies than those that received M-ORF2, pc-ORF2 or Cy-ORF2. Furthermore, mice immunized with Sc-ORF2 or M-ORF2 showed a significantly decreased or enhanced IFN-gamma level, respectively, compared with those inoculated with pc-ORF2. With respect to neutralizing antibody and IFN-gamma levels, Sc-ORF2 is a good candidate for DNA vaccination, and the secreted Cap protein appears to be an ideal antigen for use in development of vaccines against PCV2.

A new method to identify cell types that support porcine circovirus type 2 replication in formalin-fixed, paraffin-embedded swine tissues

Porcine circovirus type 2 (PCV2) is detected in high amounts within the characteristic microscopic lesions of postweaning multisystemic wasting syndrome (PMWS) affected pigs. In spite of recent advances on disease pathogenesis, the precise cell types that support viral replication are still a major issue of scientific discussion. In this study, a new methodology to detect cell types that support PCV2 replication was designed. For this purpose, two in situ hybridisation (ISH) methods were developed and applied on tissues of PMWS naturally affected pigs using two probes designed from the ORF1 sequence of the virus. While the complementary probe (CP) detected ssDNA, ORF1 mRNA and replicative form (RF) of PCV2, the RF probe (RFP) exclusively hybridised with the RF of the virus, thus, only labelling cells where PCV2 replication is taking place. Both probes demonstrated to be specific and equally sensitive by an in vitro Southern blot hybridisation assay. ISH labelling with the CP was extensive in lymphoid tissues and of variable amount in other non-lymphoid tissues. With this probe, mainly macrophage-like cells were labelled but also other cell types such as hepatocytes and other epithelial cells. Tissues in which RFP labelling was found more frequently were lung, inguinal and mesenteric lymph nodes, tonsil and liver. Labelling with the RFP was always nuclear, and found in the same cell types as with the CP, although in a relatively low proportion of them; labelling of macrophage-like cells was infrequent. Therefore, the results indicate that at least a certain proportion of macrophages may support PCV2 replication, but main cells where PCV2 replicates are of epithelial/endothelial origin. In summary, the present study permitted the study of cell types that support PCV2 replication by the use of ISH on formalin-fixed, paraffin-embedded tissues of PMWS affected pigs.

Homologous recombination plays minor role in excision of unit-length viral genomes from head-to-tail direct tandem repeats of porcine circovirus during DNA replication in Escherichia coli

In this report, we confirmed previous work that a theta-replicating bacterial plasmid containing 1.75 copies of genomic porcine circovirus (PCV) DNA in head-to-tail tandem (HTT) [a partial copy of PCV type 1 (PCV1), a complete copy of PCV type 2 (PCV2) and two origins of DNA replication (Ori)] yielded three different double-stranded DNA species when transformed into Escherichia coli: the input construct (U), the unit-length PCV1/PCV2 genome with a composite Ori lacking the plasmid vector (Q(RC)) and the remaining left-over 0.75 copy PCV1/PCV2 genome with a different composite Ori inserted in the plasmid vector (L(RC)). Replication of U was presumably via the theta-like replication mechanism utilizing the colicin E1 Ori, while derivation of L(RC) and Q(RC) was via the rolling-circle replication (RCR) copy-release mechanism and required the presence of two PCV Oris and the virus-encoded Rep protein. Essentially, excision of a unit-length PCV1/PCV2 genome (Q(RC)) via RCR from U yielded L(RC). Furthermore, we examined whether homologous recombination may also result in excision of a different type of unit-length PCV genome (Q(H)) from identical HTT constructs to generate L(H). Whereas the generation of L(RC) is Rep-protein-dependent, the generation of L(H) is Rep-protein-independent. Accordingly, the L(RC) and Q(RC) molecules derived from RCR possess different characteristics from the L(H) and Q(H) molecules generated via homologous recombination. In one of the studies in which both L(RC) and L(H) were generated simultaneously from the same HTT construct, out of 69 samples analyzed, 66 were derived via RCR and 3 were derived via homologous recombination. Thus, in comparison with RCR, homologous recombination plays a minor role in the excision of unit-length PCV genomes from HTT constructs in Escherichia coli.

Porcine circovirus diseases

Porcine circovirus type 2 (PCV2) is a member of the familyCircoviridae, a recently established virus family composed of small, non-enveloped viruses, with a circular, single-stranded DNA genome. PCV2, which is found all over the world in the domestic pig and probably the wild boar, has been recently associated with a number of disease syndromes, which have been collectively named porcine circovirus diseases (PCVD). Postweaning multisystemic wasting syndrome (PMWS), porcine dermatitis and nephropathy syndrome (PDNS) and reproductive disorders are the most relevant ones. Among them, only PMWS is considered to have a severe impact on domestic swine production. PMWS mainly affects nursery and/or fattening pigs; wasting is considered the most representative clinical sign in this disease. Diagnosis of this disease is confirmed by histopathological examination of lymphoid tissues and detection of a moderate to high amount of PCV2 in damaged tissues. Since PMWS is considered a multifactorial disease in which other factors in addition to PCV2 are needed in most cases to trigger the clinical disease, effective control measures have focused on the understanding of the co-factors involved in individual farms and the control or elimination of these triggers. PDNS, an immuno-complex disease characterized by fibrino-necrotizing glomerulonephritis and systemic necrotizing vasculitis, has been linked to PCV2, but a definitive proof of this association is still lacking. PCV2-associated reproductive disease seems to occur very sporadically under field conditions, but it has been characterized by late-term abortions and stillbirths, extensive fibrosing and/or necrotizing myocarditis in fetuses and the presence of moderate to high amounts of PCV2 in these lesions. Taking into account that scientific information on PCV2 and its associated diseases has been markedly expanded in the last 8 years, the objective of this review is to summarize the current state of knowledge of the most relevant aspects of PCV2 biology and PCVD.

Rolling-circle replication of an animal circovirus genome in a theta-replicating bacterial plasmid in Escherichia coli

A bacterial plasmid containing 1.75 copies of double-stranded porcine circovirus (PCV) DNA in tandem (0.8 copy of PCV type 1 [PCV1], 0.95 copy of PCV2) with two origins of DNA replication (Ori) yielded three different DNA species when transformed into Escherichia coli: the input construct, a unit-length chimeric PCV1(Rep)/PCV2(Cap) genome with a composite Ori but lacking the plasmid vector, and a molecule consisting of the remaining 0.75 copy PCV1(Cap)/PCV2(Rep) genome with a different composite Ori together with the bacterial plasmid. Replication of the input construct was presumably via the theta replication mechanism utilizing the ColE(1) Ori, while characteristics of the other two DNA species, including a requirement of two PCV Oris and the virus-encoded replication initiator Rep protein, suggest they were generated via the rolling-circle copy-release mechanism. Interestingly, the PCV-encoded Rep' protein essential for PCV DNA replication in mammalian cells was not required in bacteria. The fact that the Rep' protein function(s) can be compensated by the bacterial replication machinery to support the PCV DNA replication process echoes previous suggestions that circular single-stranded DNA animal circoviruses, plant geminiviruses, and nanoviruses may have evolved from prokaryotic episomal replicons.

Experimental infection of 3-week-old conventional colostrum-fed pigs with porcine circovirus type 2 and porcine parvovirus

This report describes an experimental infection with porcine circovirus type 2 (PCV2) in combination with porcine parvovirus (PPV) in 3-week-old conventional colostrum-fed pigs with maternal antibodies to both viruses. Two groups of four pigs each were inoculated with PCV2 and PPV. One of the groups received also a commercial inactivated vaccine against porcine pleuropneumonia to evaluate possible effects of the stimulation of the immune system of pigs on the infection. Another group of four pigs was kept as uninfected control. Clinical signs, rectal temperatures and body weights were recorded. Serum antibody titers to PCV2 and PPV were determined at weekly intervals. Pigs were killed 42 days after inoculation and tissue samples were examined for the presence of gross and microscopic lesions. Tissues were also analyzed for the presence of PCV2 and PPV DNA by PCR, and for the presence of PCV2 antigen by immunohistochemistry (IHC). All the pigs had serum antibodies to PCV2 and PPV at the beginning of the trial. None of them developed clinical symptoms or pathological lesions typical of post-weaning multisystemic wasting syndrome (PMWS), a disease associated to PCV2 infection. However, IHC and/or PCR analyses showed that clinically silent PCV2 infection developed in five of the eight inoculated pigs, regardless of the administration of the vaccine. In particular, PCV2 DNA and/or antigen were detected in most of the tissues examined in the two pigs with the lowest titer of maternal PCV2 antibodies at the beginning of the trial. PPV DNA was not detected in any of the samples examined. The five pigs with PCR and/or IHC evidence of PCV2 infection had a mean weight gain during the experiment lower than that of the inoculated PCR-negative pigs considered together and that of the control pigs. In conclusion, it would appear that passive immunity against PCV2 can play a role in preventing the development of PMWS, but is not able to prevent the establishing of clinically silent PCV2 infections. The dissemination and persistence of the virus in the tissues may depend on the level of PCV2 antibodies at the time of inoculation.

Effect of granulocyte-macrophage colony-stimulating factor on post-weaning multisystemic wasting syndrome in porcine circovirus type-2-transfected piglets

Post-weaning multisystemic wasting syndrome (PMWS) is a complex disease syndrome in swine, affecting nursery and fattening pigs. Although ongoing evidence suggests that porcine circovirus type-2 (PCV2) is the causal agent of PMWS, the host immune system appears to have a crucial role in the PMWS pathogenesis of PCV2-affected pigs. Owing to difficulties in producing a biologically pure form of PCV2 devoid of the other viral agents commonly present in swine tissues, we decided to use a tandem-cloned PCV2 DNA providing highly pure grade reagent in order to monitor the virulence of PCV2 alone or with an immunostimulating co-factor, granulocyte-macrophage colony-stimulating factor (GM-CSF). A single intramuscular injection of tandem-cloned PCV2 DNA into 5-week-old piglets produced plasmid to viral genome progeny and infectious particles as early as 8 days post-injection in all the organs tested (the lung, the tonsil and the inguinal, mesenteric, bronchial and upper-right axial lymph nodes). The initial plasmid load was not detected with the help of primers designed to specifically detect the acceptor plasmid, thus confirming the replication of the viral genome. Despite the presence of a high level of PCV2 genome copies in the lymphoid organs--the tonsil and the lung--and the presence of infectious particles, no detectable clinical manifestations or pathological lesions were observed in the transfected pigs over the period of observation, regardless of whether they had been co-injected with plasmid containing GM-CSF DNA or had received plasmid containing PCV2 DNA alone. GM-CSF encoding DNA injection had no significant effect on viral replication or on the production of viral particles and appearance of the disease.

Detection and in vitro and in vivo characterization of porcine circovirus DNA from a porcine-derived commercial pepsin product

Non-pathogenic porcine circovirus type 1 (PCV1) and pathogenic PCV2 are widespread in swine herds. In this study, the detection and characterization of PCV1 and PCV2 DNA from porcine-derived commercial pepsin are reported. The complete genomic sequences of the pepsin-derived PCV1 and PCV2 share 76 % nucleotide sequence identity with each other and 95–99 % identity with respective North American PCV1 and PCV2 isolates. However, the PCV-contaminated pepsin lacks infectivity in PK-15 cells. To further assess the infectivity of the contaminating pepsin in vivo, 16 5-week-old, specific-pathogen-free pigs were divided randomly into three groups: pigs in group 1 (n=5) were each inoculated intramuscularly and intranasally with 4 ml PBS buffer as negative controls, those in group 2 (n=6) were each inoculated with 400 mg contaminated pepsin dissolved in 4 ml PBS and those in group 3 (n=5) were each inoculated with 4×104·3 TCID50 PCV2 as positive controls. PCV2 viraemia, seroconversion and pathological lesions were detected in group 3 pigs, but not in group 1 or 2 pigs, confirming that the contaminating PCVs were non-infectious. Nevertheless, the detection of PCV DNA in a porcine-derived commercial product raises concern for potential human infection through xenotransplantation.