Porcine circovirus 2 replication in colostrum-deprived piglets following experimental infection and immune stimulation using a modified live vaccine against porcine respiratory and reproductive syndrome virus

Porcine circovirus type 2 (PCV2) infection is now recognized as the major factor in the development of post-weaning multisystemic wasting syndrome (PMWS). Although Koch's postulates have been fulfilled for PCV2 and PMWS, the severe clinical expression of the disease observed in field cases has been difficult to reproduce experimentally. Some studies have demonstrated that immune stimulation associated with the use of some commercially available swine vaccines may trigger progression of PCV2 infection to disease and lesions characteristic of PMWS. Here we describe the effects on PCV2 infection in an experimental model following the use of a commercially available modified live vaccine to porcine respiratory and reproductive syndrome virus (PRRSV). Although none of the piglets infected with PCV2 developed clinical PMWS, the severity of microscopical lesions and the PCV2 antigen load associated with these lesions were higher in the PRRSV-vaccinated piglets compared with those detected in the PCV2 only infected animals.     

Porcine circovirus type 2 and associated diseases in Romania--short communication

Porcine circovirus type 2 (PCV2) has been demonstrated to be the causal agent for postweaning multisystemic wasting syndrome (PMWS) and porcine dermatitis and nephropathy syndrome (PDNS). This report describes the first detection of PCV2 and associated diseases in a Romanian swine herd located in Transylvania. The clinical signs, pathological and histopathological changes observed in affected pigs were similar to those previously described for PDNS and PMWS. Polymerase chain reaction and in situ hybridisation were used for the detection of PCV2 nucleic acids from tissues and serum samples. Complete PCV2 genomes of both PMWS and PDNS cases were sequenced and analysed, and by comparing them with each other no genomic differences could be detected. The sequence analysis showed that the Romanian PCV2 was closely related to PCV2 identified in France and in Hungary.     

Myocarditis and abortion associated with intrauterine infection of sows with porcine circovirus 2.

Porcine circovirus 2 (PCV2) is a recently identified agent that has been associated with postweaning multisystemic wasting syndrome (PMWS) in swine populations. In this report, the potential spectrum of disease associated with PCV2 is expanded by evidence of vertical transmission and associated reproductive failure. PCV2 was isolated from a litter of aborted piglets from a farm experiencing late-term abortions and stillbirths. Severe, diffuse myocarditis was present in 1 piglet associated with extensive immunohistochemical staining for PCV2 antigen. Variable amounts of PCV2 antigen were also present in liver, lung, and kidney of multiple fetuses. The presence of other agents that have been associated with fetal lesions and abortion in swine, including porcine parvovirus, porcine reproductive respiratory syndrome virus, encephalomyocarditis virus, and enterovirus, could not be established.     

Porcine circovirus diseases

Porcine circovirus type 2 (PCV2) is a member of the family Circoviridae, 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.     

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.     

First report of post-weaning multisystemic wasting syndrome and porcine dermatitis and nephropathy syndrome in pigs in Greece

Post-weaning multisystemic wasting syndrome (PMWS) and porcine dermatitis and nephropathy syndrome (PDNS) are two recently described conditions of pigs at the late nursery and fattening stages. The aim of this short communication was to describe the first reported occurrence of these conditions and of porcine circovirus type 2 (PCV2) infection in Greece. The clinical signs, gross post-mortem changes and histopathological changes observed in affected pigs, were similar to those previously described for both PDNS and PMWS. As in previous reports, the lesions were associated with PCV2 infection, which was demonstrated by immunohistochemical and in situ hybridization methods.     

The clinical expression and emergence of porcine circovirus 2

Since its discovery and characterization in western Canada in 1995, the distribution of post-weaning multisystemic wasting syndrome (PMWS) has grown and the syndrome is undoubtedly recognized worldwide. More recently, there is a heightened interest in several potentially related conditions including porcine dermatitis and nephropathy syndrome (PDNS), proliferative and necrotizing pneumonia (PNP), congenital tremors (CT-AII), perinatal myocarditis and reproductive failure. Although the causality of porcine circovirus type 2 (PCV2) has recently been proven [Vet. Pathol. 37 (2000) 254; J. Comp. Pathol. 122 (2000) 9; J. Vet. Diagn. Invest. 13 (2001) 185], PCV2 is present in both diseased and healthy pig populations. Furthermore, recent serologic studies have shown that there are no significant differences in PCV2 specific IgG titres between PMWS clinical and non-clinical herds (Harding et al., in press). Clearly, the transmission, epidemiology, and factors triggering clinical expression are poorly understood. With these uncertainties in mind, the objective of this paper is to review the clinical expression and emergence of PMWS and the potentially associated disease syndromes including PDNS.     

A review of porcine circovirus 2-associated syndromes and diseases

Clinical expression of porcine circovirus 2 (PCV2) infection in swine may result in several distinct syndromes and diseases including post-weaning multisystemic wasting syndrome (PMWS), porcine dermatitis and nephropathy syndrome (PDNS), reproductive failure, porcine respiratory disease complex, granulomatous enteritis, necrotizing lymphadenitis, and possibly exudative epidermitis. Association of PCV2 with congenital tremor in piglets is still controversial. The extent of the involvement of PCV2 in swine disease other than PMWS is currently poorly understood. This review concentrates on PCV-2-associated syndromes and diseases other than PMWS.     

First Report of Post‐Weaning Multisystemic Wasting Syndrome and Porcine Dermatitis and Nephropathy Syndrome in Pigs in Greece

Post‐weaning multisystemic wasting syndrome (PMWS) and porcine dermatitis and nephropathy syndrome (PDNS) are two recently described conditions of pigs at the late nursery and fattening stages. The aim of this short communication was to describe the first reported occurrence of these conditions and of porcine circovirus type 2 (PCV2) infection in Greece. The clinical signs, gross post‐mortem changes and histopathological changes observed in affected pigs, were similar to those previously described for both PDNS and PMWS. As in previous reports, the lesions were associated with PCV2 infection, which was demonstrated by immunohistochemical and in situ hybridization methods.     

Temporal distribution of porcine circovirus 2 genogroups recovered from postweaning multisystemic wasting syndrome affected and nonaffected farms in Ireland and Northern Ireland.

Porcine circovirus type 2 (PCV2) is now recognized as the essential infectious component of porcine postweaning multisystemic wasting syndrome (PMWS). PMWS was first recognized in high-status, specific pathogen-free pigs in Canada in 1991 and is now an economically important disease that affects the swine industry around the world. Recently, reports of genomic studies on PCV2 viruses indicated that 2 distinctive genogroups of PCV2 exist.4,10 This report involves the results of a study on the distribution of predominant PCV2 genogroups recovered from samples taken from PMWS-affected and PMWS-nonaffected farms on the island of Ireland over a 9-year period and the results of a study on PCV2 genogroup recovery from fecal samples taken from a farm in Northern Ireland from 2003 to 2005 that was first diagnosed as PMWS positive in August 2005. The results indicate that, although at least 2 distinct genogroups of PCV2 have been circulating on pig farms on the island of Ireland, there does not appear to be a direct relationship between infection with these different genogroups of PCV2 and the development of PMWS.     

Case-control study on the association of porcine circovirus type 2 and other swine viral pathogens with postweaning multisystemic wasting syndrome.

A field-based case-control study was conducted to assess the strength of association of porcine circovirus type 2 (PCV2) and some major swine viruses with postweaning multisystemic wasting syndrome (PMWS). Cases were defined as individual pigs with a clinical history of progressive weight loss and histopathological lesions characteristic of PMWS. Controls were pigs without clinical signs and histopathological lesions typical of PMWS. A total of 31 cases and 56 controls was identified from diagnostic submissions. Serum and various tissues were collected from all animals and assayed for PCV, porcine reproductive and respiratory syndrome virus (PRRSV), porcine parvovirus, porcine enterovirus types 1-3, swine influenza virus, porcine respiratory coronavirus, transmissible gastroenteritis virus, porcine endogenous retrovirus, porcine lymphotropic herpesvirus type 1, and bovine viral diarrhea virus. The proportion of case and control pigs positive for each virus was determined and statistically compared for determining the strength of the association that each virus had with PMWS individually or in combinations. Porcine circovirus type 2 had the strongest association (OR = 9.3, P = 0.006) with PMWS among the viruses tested for. Risk for PWMS was much higher (OR = 31.2, P = 0.0009) if the animal was concurrently infected with PCV2 and PRRSV, suggesting that development of PMWS may be enhanced by cofactor(s). Because PCV2 was also found in 62.5% of the controls, PCV2 from 5 cases and 4 controls were selected and genetically compared. No significant genetic difference was observed between PCV2 from PMWS and control pigs.     

Postweaning multisystemic wasting syndrome (PMWS) in pigs. A review

Postweaning multisystemic wasting syndrome, caused by porcine circovirus type 2 (PCV2), is a recently described clinical condition which affects nursery and growing pigs. PMWS was initially recognized in Canada in 1991 and nowadays is considered to be worldwide distributed. Clinically, PMWS most representative symptoms include wasting, unthriftness, paleness of the skin, respiratory distress, diarrhea and sometimes icterus. PCV2 infection occurs in both PMWS affected and non-affected farms, and viral seroconversion shows a typical pattern, with declining of colostral antibodies during the lactating and nursery periods, with the lowest levels at the end of the nursery period, and active seroconversion of almost all pigs during the grower period. Although antibodies to PCV2 have been detected as early as 1969, no explanation for the emergence of this disease in the 90s has been established. Macroscopic lesions associated with PMWS are quite unspecific, but histopathological lesions in lymphoid tissues (lymphocyte depletion with histiocytic infiltration) are almost unique for this disease. These lesions together with other clinical and laboratorial findings suggest that severely affected pigs may be immunosuppressed. The criteria used for the diagnosis of PMWS include the existence of compatible clinical signs, presence of characteristic microscopic lesions and detection of PCV2 within these lesions. Because of the lack of appropriate treatment or vaccination against PCV2, zootechnical changes have been proposed in affected farms to reduce the so-called "infection pressure" due to PCV2 as well as to any other pathogen.     

Experimental reproduction of postweaning multisystemic wasting syndrome (PMWS) in pigs in Sweden and Denmark with a Swedish isolate of porcine circovirus type 2

An experimental model using 3-day-old snatch-farrowed colostrum-deprived piglets co-infected with porcine circovirus type 2 (PCV2) and porcine parvovirus (PPV) is at present one of the best methods to study factors affecting development of postweaning multisystemic wasting syndrome (PMWS). A Swedish isolate of PCV2 (S-PCV2) retrieved in 1993 from a healthy pig has been used in this model to reproduce PMWS in pigs from Northern Ireland. This virus has been present in the Swedish pig population for at least a decade without causing any known PMWS disease problems, despite its potential pathogenicity. The reasons for this are unknown, but could be related to genetics, absence of triggers for PCV2 upregulation (infectious agent and/or management forms) within Swedish pig husbandry. In order to confirm the pathogenicity of S-PCV2, Swedish and Danish pigs were experimentally infected with this isolate according to the established model. Swedish pigs were also infected with a reference isolate of PCV2 (PCV2-1010) to compare the severity of disease caused by the two isolates in Swedish pigs. Both Danish and Swedish pigs developed PMWS after the experimental infection with S-PCV2. Antibodies to PCV2 developed later and reached lower levels in serum from pigs infected with S-PCV2 than in pigs inoculated with PCV2-1010. In general, pigs infected with S-PCV2 showed more severe clinical signs of disease than pigs infected with PCV2-1010, but pigs from all PCV2-inoculated groups displayed gross and histological lesions consistent with PMWS. All pigs inoculated with PPV, alone or in combination with PCV2, displayed interleukin-10 responses in serum while only pigs infected with PPV in combination with PCV2 showed interferon-alpha in serum on repeated occasions. Thus, the pathogenicity of S-PCV2 was confirmed and a role for cytokines in the etiology of PMWS was indicated.     

猪圆环病毒2型疫苗研究进展

猪圆环病毒2型(PCV2)感染后会导致断奶仔猪多系统衰竭综合征(PMWS)等"猪圆环病毒相关疾病"(PCVADs),给全球养猪业造成了巨大的经济损失。疫苗免疫是防控该病的有效手段,近年来市场上推出了PCV2灭活疫苗、嵌合疫苗和亚单位疫苗。PCV2变异较快,主要临床流行毒株从PCV2b逐渐演变为PCV2d,现有商业化疫苗免疫效果需进一步研究证实。论文就近年来国内外PCV2传统疫苗、新型基因工程疫苗、PCV2疫苗与其他疫苗联合免疫的研究进展进行综述,旨在为猪圆环病毒相关疾病的防控及疫苗的开发与利用提供参考。     

Recent advances in the epidemiology,diagnosis and control of diseases caused by porcine circovirus type 2

Post-weaning multisystemic wasting syndrome (PMWS) emerged as a significant disease affecting pig production in the 1990s although the causal agent, porcine circovirus type 2 (PCV2), and the disease itself, had existed in swine for many years prior to this. The important multifactorial ‘triggers’ of PMWS include the immune and infection status of the sow, the timing of PCV2 infection, variations in the virulence of PCV2, co-infections, immune modulation as well as host genetics and management factors. In terms of diagnosis, histopathological examination and the detection of PCV2 within lymphoid tissue remains the ‘gold standard’ as quantitative PCR techniques are currently not specific or sensitive enough. The recent commercial availability of PCV2 vaccines provides an excellent tool for reducing the impact of PMWS and other porcine circovirus-related diseases. This review assesses recent advances in the epidemiology, diagnosis and control of PMWS.     

Reproduction of PMWS in immunostimulated SPF piglets transfected with infectious cloned genomic DNA of type 2 porcine circovirus

Postweaning multisystemic wasting syndrome (PMWS) is a recently emerged disease affecting pigs. Type 2 porcine circovirus (PCV2) has been associated with this syndrome although other factors are required in association with this virus for PMWS expression. The aim of this study was to investigate whether general immunostimulation (injections of keyhole limpet hemocyanin emulsified in incomplete Freund adjuvant and of thioglycollate medium) could strengthen the severity of PMWS in six-week-old specific-pathogen-free (SPF) piglets transfected with pure tandem-cloned PCV2 DNA by the intramuscular route. Non-immunostimulated piglets transfected with the viral clone did not present clinical signs but only mild pathological microlesions characteristic of PMWS. These piglets seroconverted and high viral genome loads and infectious titers were detected in the lymphoid organs at the end of the trial. Mild-to-moderate forms of PMWS were generally observed in the immunostimulated transfected piglets, as well as one severe form for a piglet (8003) which died. These piglets with mild-to-moderate forms had higher DNA loads than the transfected-only animals. Thus, viral replication was enhanced by immunostimulation. This is the first time that clinical PMWS has been reported in an SPF immunostimulated piglet infected with a pure inoculum consisting of tandem-cloned PCV2 DNA. This result confirms that PCV2 is the agent of PMWS and that immunostimulation could enhance PMWS in SPF piglets transfected with a PCV2 DNA clone.     

Detection and genetic characterization of porcine circovirus type 2 (PCV2) in pigs from Croatia

Porcine circovirus type 2 (PCV2) from the Circoviridae family has recently been associated with two serious diseases of swine, post-weaning multisystemic wasting syndrome (PMWS) and porcine dermatitis and nephropathy syndrome (PDNS). During 2002, several outbreaks of clinical disease in pigs with weights ranging from 10 to 70 kg occurred on four farms in different locations in Croatia. The signs were consistent with PMWS and PDNS. Apart from progressive weight loss, pneumonia and/or diarrhoea, multifocal erythematous skin lesions and dermal necrosis were also observed. The PCR results obtained from PCV2 specific oligonucleotide primers confirmed a PCV2 infection. In addition, archive samples that were classical swine fever virus positive and derived from domestic pigs during an outbreak in 1997 were included in this study and one out of the three isolates was found to be positive for PCV2. For a better epizootiological understanding, genetic typing of representative isolates was carried out and compared with available isolates reported in the GenBank databases.     

A novel method for the detection of porcine circovirus type 2 replicative double stranded viral DNA and nonreplicative single stranded viral DNA in tissue sections.

Porcine circovirus type 2 (PCV2), an economically important pathogen of swine, is the necessary cause of post weaning multisystemic wasting disease (PMWS); PCV2 infection is associated with porcine dermatitis and nephritis syndrome (PDNS). Current immunohistochemical (IHC) methodologies identify PCV2 antigens but are not capable of differentiating replicating virus from nonreplicating virion particles in tissue sections. In this paper, a combination of IHC using commercial monoclonal antibodies specific for single stranded (ss) and double stranded (ds) DNA and PCV2 specific in situ hybridization (ISH) was used to show the specificity of the former for PCV2 DNA in tissue sections from PCV2-infected gnotobiotic pigs. Cold-ethanol-fixed tissue sections were superior to formalin-fixed tissues for detection of PCV2 DNA, presumably due to the lack of protein cross-linking in the latter. These data demonstrate that conventional IHC detects PCV2 DNA forms in experimentally infected PCV2-positive gnotobiotic porcine tissue sections that are minimally compromised by either formalin fixation or the hybridization conditions needed for ISH.     

Coinfection by porcine circoviruses and porcine parvovirus in pigs with naturally acquired postweaning multisystemic wasting syndrome.

Postweaning multisystemic wasting syndrome (PMWS) is an emerging disease in swine. Recently, the disease has been reproduced with inocula containing a newly described porcine circovirus (PCV), designated PCV 2, and porcine parvovirus (PPV). In order to determine if these viruses interact in naturally acquired PMWS, affected tissues from field cases were examined by immunohistochemistry (IHC) and polymerase chain reaction (PCR) for PCV 2 and PPV, as well as by PCR for the other recognized porcine circovirus, PCV 1. Porcine circovirus 2 was detected by PCR or IHC in affected fixed or frozen tissues from 69 of 69 cases of PMWS collected over 3 years from 25 farms. Porcine parvovirus was detected in 12 of the same cases, and PCV 1 was detected in 9 of 69; however, an apparent decrease was found in the sensitivity of the PCRs used to detect the latter 2 viruses when fixed tissue from the same cases were compared with the use of frozen tissues. Porcine circovirus 2 was not detected by PCR in affected tissues from 16 age-matched pigs that had Streptococcus suis-associated disease. Electron microscopic examination of plasma pooled from 15 pigs with PMWS revealed the presence of PCV and PPV, whereas these viruses were not observed in pooled plasma from 5 age-matched clinically normal pigs. These results confirm and extend previous findings documenting a consistent association of PCV 2 with PMWS. As well, infection by PPV or PCV 1 or both may be an important cofactor in the pathogenesis of some, but apparently not all, cases of PMWS.     

Porcine dermatitis and nephropathy syndrome (PDNS) is associated with a systemic cytokine expression profile indicative of proinflammation and a Th1 bias

Porcine dermatitis and nephropathy syndrome (PDNS) is broadly discussed as a porcine circovirus type 2 (PCV2)-associated disease, although PCV2, in contrast to postweaning multisystemic wasting syndrome (PMWS), has to date not been proven to be the aetiologic agent. In order to better understand the complex immunopathology of PDNS, the systemic cytokine expression profiles of (i) five pigs suffering from PDNS, (ii) five animals suffering from naturally acquired PMWS and (iii) five controls were investigated at mRNA and protein levels by means of multiplex real-time RT-PCR and flow cytometric intracellular cytokine detection, respectively. IL-1alpha, IL-6 and IFN-gamma mRNA expressions were found to be elevated in PDNS pigs. At the protein level, an increased capacity of peripheral blood mononuclear cells to produce IL-2, IL-4, IL-6, IL-12, TNF-alpha and IFN-gamma was evident. Hematological investigations revealed a hypochromic anemia while basophils and monocytes were relatively and neutrophils absolutely increased in PDNS pigs. PCV2 antibody levels did not differ significantly between PDNS and PMWS affected animals. Taken results together, the cytokine profile of the PDNS affected animals together with hematological data pointed towards a proinflammatory condition supporting a Th1 bias. Cytokine data of PMWS affected animals exhibited only minor non-significant differences when compared to controls, only IL-10 was significantly decreased at the mRNA level.