Induction of porcine post-weaning multisystemic wasting syndrome (PMWS) in pigs from PMWS unaffected herds following mingling with pigs from PMWS-affected herds

In this paper we present the results from two experimental studies (I and II) investigating whether post-weaning multisystemic wasting syndrome (PMWS) can be induced in pigs from PMWS unaffected herds by mingling with pigs from PMWS-affected herds and to observe whether transportation and/or mingling of healthy pigs from unaffected herds could induce PMWS.The studies comprised pigs from 12 different herds. Eight herds had PMWS while four were unaffected. All 12 herds were found to be infected with PCV2. Pigs from PMWS-affected herds were mingled with pigs from unaffected herds in four separate compartments in both study I and study II. In addition, in study II, four groups of pigs from unaffected herds were included. Two groups with pigs transported and mingled from unaffected herds and two groups with pigs which were only transported. The PMWS diagnoses on the individual pigs were based on lymphoid depletion, histiocytic proliferation and the presence of giant cells or inclusion bodies together with the demonstration of PCV2 in lymphoid tissue.Healthy pigs, in both studies, developed PMWS 4–5 weeks after mingling with pigs clinically affected with PMWS. None of the pigs from unaffected herds which had no contact with pigs from PMWS-affected herds developed clinical signs of PMWS. Transportation and mingling of pigs from PMWS unaffected herds in combination or alone was insufficient to provoke PMWS.     

Pathological investigations of pigs with porcine multisystemic wasting syndrome (PMWS)

Extract

Pathological changes and immunohistochemical (IHC) examination for porcine circovirus-2 (PCV-2) in nine weaner pigs from a property with PMWS are reported. The pigs were in moderate to poor body condition, and several had diarrhoea and noisy respiration. The outstanding pathological changes related to microscopic lesions in lymphoid tissues, including lymph nodes, palatine tonsils, Peyer's patches, peribronchial lymphoid aggregates and spleen. While there was variability of expression of change between and within cases, the main features of lesions could be summarised as depletion of lymphoid cells, infiltration of histiocytes (often syncytial), and the presence of botryoid intra-cytoplasmic inclusion bodies in macrophages. The changes in lymphoid tissue were typical of those described in PMWS. Also characteristic of this syndrome were histiocyte-dominated cellular inflammatory infiltrates in kidney, liver and lung. There was strong correlation between IHC positivity for PCV-2 and the lesions in lymphoid, pulmonary and renal tissues. Concurrent diseases that are probably promoted by immune suppression may complicate the diagnosis of PMWS. In the present cases, salmonellosis, attaching and effacing Escherichia coli infections, and secondary bacterial bronchopneumonia were identified.     

Differentiation of porcine circovirus 1 and 2 in formalin-fixed, paraffin-wax-embedded tissues from pigs with postweaning multisystemic wasting syndrome by in-situ hybridisation

Non-radioactive digoxigenin (DIG)-labelled probes that can differentiate porcine circovirus (PCV) 1 from PCV2 in formalin-fixed, paraffin-wax-embedded tissues by in-situ hybridisation were developed. A 349 base pair (bp) DNA fragment from open reading frame (ORF) 1 of PCV1 and a 481 bp DNA fragment from ORF2 of PCV2 generated by polymerase chain reaction (PCR) were used as PCV1 and PCV2 probes, respectively. A specific DIG-labelled PCV1 DNA probe did not hybridise with PCV2-infected PK-15 cells and vice versa. From the 40 field cases with postweaning multisystemic wasting syndrome tested by in-situ hybridisation, 30 (75 per cent) cases were PCV2-positive only and 10 (25 per cent) cases were positive for both PCV1 and PCV2. PCV1 and PCV2 DNAS were detected mainly in the macrophages of lymph nodes and spleens. Positive cells typically exhibited a dark brown to black reaction product mainly in the cytoplasm but also occasionally in the nucleus. In-situ hybridisation together with the differential probes developed in the present study represent an additional tool capable of differentiating of both types of PCV in formalin-fixed, paraffin-wax-embedded tissues.     

Association of lymphopenia with porcine circovirus type 2 induced postweaning multisystemic wasting syndrome (PMWS)

The composition of peripheral blood leukocyte populations was studied following experimental PCV2-infection in 3-week-old piglets. Four of 10 PCV2-infected piglets developed clinical and pathological symptoms consistent with postweaning multisystemic wasting syndrome (PMWS) between 14 and 21 days post-inoculation (p.i.), and were characterised as PMWS-affected. Only these four PMWS-affected piglets, but neither the non-symptomatic infected nor control animals, developed a clear leukopenia. Kinetic analysis demonstrated a clear loss of both CD21(+) B and CD3(+) T lymphocytes in the PMWS-affected piglets. By CD3/CD4/CD8 triple labelling, the influence of PCV2 infection on all T cell sub-populations was discernible. A loss of CD3(+)CD4(+)CD8(+) memory/activated Th lymphocytes was particularly notable. However, all T lymphocyte sub-populations-CD3(+)CD4(+)CD8(+) memory Th, CD3(+)CD4(+)CD8(-) nai;ve Th, CD3(+)CD4(-)CD8(+) Tc and CD3(+)CD4(-)CD8(-) gammadelta TCR(+) lymphocytes-were susceptible to PCV2 infection-induced lymphopenia. CD3(-)CD4(-)CD8(+) NK cells were also depleted in the PMWS-affected animals, but granulocytes and monocytes were less affected. In conclusion, PCV2 infection induces primarily a lymphopenia, but only in animals which subsequently develop PMWS. The lymphopenia can be identified early p.i., particularly with the B lymphocytes. Memory/activated Th lymphocytes might be affected more than the other T cell sub-populations, but as time progressed a collapse of both T and B cell populations was clear.     

Risk factors for porcine post-weaning multisystemic wasting syndrome (PMWS) in 149 French farrow-to-finish herds

A cross-sectional study involving 149 farms was carried out in France in 2000 and 2001 to assess the risk factors for post-weaning multisystemic wasting syndrome (PMWS). The farms were divided into three groups according to their current or past PMWS status: CASES (current and typical PMWS), CONTROLS#1 (PMWS-free farms), and CONTROLS#2 (farms which have recovered from PMWS). Two different comparisons were tested: CASES versus CONTROLS#1 and CASES versus CONTROLS#2. In the first comparison, the odds of PMWS were increased when fattening pigs tested positive for parvovirus (PPv) and porcine reproductive and respiratory syndrome (PRRS) virus (OR=4.4 and 6.5, respectively), when separate vaccines for parvovirus and Erysipela for the gilts versus associated vaccines were used (OR=2.5), and when on-farm semen collection was used versus all the semen purchased from an insemination centre (OR=4.6). Large pens in weaning facilities increased the odds of PMWS (OR=4.1); whereas long empty periods in weaning and farrowing facilities versus shorter (OR=0.2), regular treatment against external parasites (OR=0.1), and housing the sows in collective pens during pregnancy versus individual pens (OR=0.3) all decreased the odds of PMWS. The same kinds of risk factors were found with the second comparison with, in addition, a common pit for several adjacent fattening rooms versus separate pits (OR=6.7) and a high level of cross-fostering (OR=5.1). On the other hand, when farms had a self-replacement scheme for the gilts (OR=0.1), and when vaccination of the sows against E. coli was in place (OR=0.2), the odds of PMWS were decreased.     

Porcine circovirus type 2 (PCV-2) coinfections in US field cases of postweaning multisystemic wasting syndrome (PMWS).

The prevalence of different pathogens detected in combination with porcine circovirus type 2 (PCV-2) was studied retrospectively in field cases of postweaning multisystemic wasting syndrome (PMWS) diagnosed at the Iowa State University Veterinary Diagnostic Laboratory, Ames, Iowa, between January 2000, and September 2001. The presence of PCV-2 antigen in lymphoid tissues and/or lung, demonstrated by immunohistochemistry, together with moderate to severe lymphoid depletion and/or granulomatous lymphadenitis, was used as the criteria for the diagnosis of PMWS. A total of 484 cases fulfilled these criteria. Most of the cases (294/369) of PMWS occurred in pigs between the ages of 8 and 18 weeks, with a peak at 10 weeks of age. Porcine reproductive and respiratory syndrome virus was detected in 51.9% of the cases, Mycoplasma hyopneumoniae in 35.5%, bacterial septicemia in 14.0%, bacterial pneumonia in 7.6%, swine influenza virus in 5.4%, and PCV-2 alone in 1.9%. In cases with bacterial septicemia the most frequently isolated pathogen was Streptococcus suis. In cases with bacterial pneumonia, Pasteurella multocida was the most prevalent.     

Porcine circovirus type 2-associated cerebellar vasculitis in postweaning multisystemic wasting syndrome (PMWS)-affected pigs

Porcine circovirus type 2 (PCV2) is associated with several syndromes in growing pigs, including postweaning multisystemic wasting syndrome and porcine dermatitis and nephropathy syndrome. In the present study, a previously undescribed neurovascular disorder associated with a PCV2 infection is described. Sixteen pigs showed clinical signs of wasting and neurologic deficits. Acute hemorrhages and edema of cerebellar meninges and parenchyma due to a necrotizing vasculitis resulted in degeneration and necrosis of the gray and white matter. Few to numerous PCV2 DNA and antigen-bearing endothelial cells were detected in affected areas of the brain using in situ hybridization and immunohistochemistry. Conventional histochemical stains, as well as the detection of caspase 3 activity and DNA strand breaks by the terminal transferase dUTP nick end labeling assay, showed numerous apoptotic endothelial cells in the vascular lesions observed. Sequencing of various brain-derived PCV2-specific amplicons revealed a strong identity between different isolates and an 89 to 100% identity to previous isolates. The phylogenetic tree showed that there was no clustering of isolates correlating to clinical signs or geographic distribution. This previously undescribed PCV2-associated neurologic disease has features of both postweaning multisystemic wasting syndrome and, to a lesser extent, porcine dermatitis and nephropathy syndrome. The available evidence suggests that direct virus-induced apoptosis of endothelial cells plays a role in the pathogenesis of this unusual PCV2-associated cerebellar vasculitis.     

Postweaning multisystemic wasting syndrome (PMWS) in pigs in Croatia: detection and characterisation of porcine circovirus type 2 (PCV2)

The objective of this study was to characterise porcine circovirus type 2 (PCV2) from pigs with naturally occurring postweaning multisystemic wasting syndrome (PMWS) in Croatia, and to determine the epizootiological, clinical and pathomorphological features of the disease. During a systematic health monitoring programme conducted in the period from January 2002 to June 2003, PMWS was suspected on eight different pig-producing farms in Croatia. The diagnosis of PMWS met all three key criteria: the presence of compatible clinical signs, the presence of the characteristic microscopic lymphoid lesions, and the detection of PCV2 within the lesions by polymerase chain reaction (PCR) and by in situ hybridisation (ISH). Moreover, PCV2 DNA from swine tissues was extracted and sequenced. The phylogenetic analysis of 4 Croatian PCV2 strains showed close relationship to PCV2 strains isolated in Slovenia, France, the Netherlands, the United Kingdom, China and Hungary. PCV2 was also demonstrated by electron microscopy in the lymph node of an affected animal. This is the first demonstration of PMWS in Croatia based on all scientifically accepted diagnostic criteria.     

Descriptive summary of an outbreak of porcine post-weaning multisystemic wasting syndrome (PMWS ) in New Zealand

CASE HISTORY: Investigations were conducted to determine the cause of an acute, multi-farm outbreak of porcine respiratory disease that included diarrhoea and subsequent loss of body condition in affected pigs. A definition for post-weaning multisystemic wasting syndrome (PMWS) including both clinical and pathological features, previously developed for the pig industry in New Zealand, was applied to the current outbreak. In addition to self-reporting by owners of affected farms, local veterinarians, disease and epidemiology consultants, and animal health officials from the Ministry of Agriculture and Forestry (MAF) were involved in conducting farm visits and submission of diagnostic specimens. CLINICAL FINDINGS AND DIAGNOSIS: Pathogens known to be endemic in the pig industry in New Zealand as well as likely exotic diseases were excluded as causative agents of the outbreak. Clinical signs including dyspnoea, diarrhoea, and rapid loss of body condition were consistent with the New Zealand case definition for PMWS. Interstitial pneumonia, pulmonary oedema, generalised lymph-node enlargement, and presence of porcine circovirus type 2 (PCV2) inclusion bodies were consistently identified in affected pigs. Classical swine fever virus (CSFv), Porcine reproductive and respiratory syndrome virus (PRRSv), and Influenza virus were ruled out, using molecular and traditional virological techniques. Spread of the disease between farms was hypothesised to be facilitated by locally migrating flocks of black-backed seagulls. The original source of the disease incursion was not identified. DIAGNOSIS: Based on the consistent presence of circovirus-associated lesions in lymphoid tissues in combination with generalised enlargement of lymph nodes, histiocytic interstitial pneumonia, clinical wasting, and poor response to antibiotic therapy, a diagnosis of PMWS was made. CLINICAL RELEVANCE: PMWS should be considered in the differential diagnoses of sudden onset of respiratory dyspnoea, diarrhoea, and rapid loss of body condition in young pigs in New Zealand pig herds.     

Isolation and characterization of porcine circovirus type 2 from pigs showing signs of post-weaning multisystemic wasting syndrome in The Netherlands

Pigs with wasting syndrome were examined for macroscopic and histopathological lesions, and for porcine circovirus (PCV). Histopathological lesions were comparable to those previously documented for post-weaning multisystemic wasting syndrome (PMWS). In addition, in seven out of ten examined PMWS-affected pigs focal-to-slight mononuclear meningitis and focal cerebral mononuclear infiltrates (4 out of 10) were observed. A virus was isolated from organs and sera from pigs showing wasting syndrome. An immunoperoxidase monolayer assay and an indirect immunofluorescence assay were performed on the infected PK-15 and Dulac cell cultures, respectively, and both assays indicated the presence of PCV type 2 (PCV2). The nested-polymerase chain reaction (nPCR) technique, based on the use of PCV2 specific oligonucleotides, revealed specific amplified products of 481 bp. Nucleotide sequence analysis of the entire genome of the Dutch PCV isolate 24657 NL showed a homology with known nucleotide sequences of porcine PCV type 1 (PCV1) and PCV2 isolates of 77.1% and >96%, respectively. This is the first report of the isolation and characterization of PCV2 in PMWS-affected pigs in the Netherlands.     

Descriptive summary of an outbreak of porcine post-weaning multisystemic wasting syndrome (PMWS) in New Zealand

CASE HISTORY: Investigations were conducted to determine the cause of an acute, multi-farm outbreak of porcine respiratory disease that included diarrhoea and subsequent loss of body condition in affected pigs. A definition for post-weaning multisystemic wasting syndrome (PMWS) including both clinical and pathological features, previously developed for the pig industry in New Zealand, was applied to the current outbreak. In addition to self-reporting by owners of affected farms, local veterinarians, disease and epidemiology consultants, and animal health officials from the Ministry of Agriculture and Forestry (MAF) were involved in conducting farm visits and submission of diagnostic specimens.

CLINICAL FINDINGS AND DIAGNOSIS: Pathogens known to be endemic in the pig industry in New Zealand as well as likely exotic diseases were excluded as causative agents of the outbreak. Clinical signs including dyspnoea, diarrhoea, and rapid loss of body condition were consistent with the New Zealand case definition for PMWS. Interstitial pneumonia, pulmonary oedema, generalised lymph-node enlargement, and presence of porcine circovirus type 2 (PCV2) inclusion bodies were consistently identified in affected pigs. Classical swine fever virus (CSFv), Porcine reproductive and respiratory syndrome virus (PRRSv), and Influenza virus were ruled out, using molecular and traditional virological techniques. Spread of the disease between farms was hypothesised to be facilitated by locally migrating flocks of black-backed seagulls. The original source of the disease incursion was not identified.

DIAGNOSIS: Based on the consistent presence of circovirusassociated lesions in lymphoid tissues in combination with generalised enlargement of lymph nodes, histiocytic interstitial pneumonia, clinical wasting, and poor response to antibiotic therapy, a diagnosis of PMWS was made.

CLINICAL RELEVANCE: PMWS should be considered in the differential diagnoses of sudden onset of respiratory dyspnoea, diarrhoea, and rapid loss of body condition in young pigs in New Zealand pig herds.     

An ORF2 protein-based ELISA for porcine circovirus type 2 antibodies in post-weaning multisystemic wasting syndrome

Porcine circovirus type 2 (PCV2) plays a crucial role in the pathogenesis of post-weaning multisystemic wasting syndrome (PMWS) in swine. As PCV2 displays significant homology with PCV1 (a non-pathogenic virus) at the nucleotide and amino-acid level, a discriminative antigen is needed for specific serological diagnosis. The ORF2-encoded capsid protein from PCV2 was used to develop an indirect enzyme-linked immunosorbent assay (ELISA). GST-fused capsid protein from PCV2 and GST alone (both expressed in recombinant baculovirus-infected cells) were used as antigens for serodiagnosis. The specificity of the ELISA for detection of PCV2 antibodies was demonstrated in sera from pigs experimentally infected with PCV1, PCV2 and other swine viruses. The semi-quantitative nature of the test was evaluated versus an immunoperoxidase monolayer assay (IPMA). The ELISA was performed on 322 sera from pigs in eight Brittany herds and compared with IPMA. The sensitivity (98.2%) and specificity (94.5%) of this test were considered suitable for individual serological detection. High PCV2 seroprevalence was found in sows and pigs at the end of the growth phase (18-19 weeks) in all eight herds. The seroprevalence in piglets (11-17 weeks) was statistically correlated with clinical symptoms of PMWS (93% in affected versus 54%, in non-affected farms). A cohort study performed in PMWS-free farms showed that 57% of piglets exhibited active seroconversion after 13 weeks, indicating that PCV2 infection occurred earlier in PMWS-affected piglets.     

Sow porcine circovirus type 2 (PCV2) status effect on litter mortality in postweaning multisystemic wasting syndrome (PMWS)

Previous studies have described a "litter effect" associated with mortality in postweaning multisystemic wasting syndrome (PMWS) affected farms. The main objective of this study was to evaluate litter mortality in different PMWS affected farms and to characterize it in relation to three variables of the sow: parity, porcine circovirus type 2 (PCV2) infectious status and PCV2 antibody titres. The study was performed in seven farms that experienced PMWS in nurseries and/or fattening areas. Fifteen sows from each farm were randomly selected from the same farrowing batch. Serum samples were analyzed for antibodies to PCV2 and for genomic detection of PCV2. Four piglets from each sow (60 piglets per farm) were selected and ear-tagged at birth. Out of 420 initial piglets, 104 (25%) died. Sixty three of them (60%) were necropsied, and 40 (63%) diagnosed as PMWS based on case definition criteria. Our results show that sow PCV2 viremia was significantly related to piglet mortality since more piglets per litter died from viremic than from non-viremic sows. Additionally, a significantly greater proportion of animals died from sows that had low antibody titres against PCV2 (39% vs. 18% from sows with medium to high antibody titres). The present study, of exploratory nature, confirms previous results and further characterizes the so called "litter effect" by establishing that the sow PCV2 status had a significant effect on litter mortality in PMWS affected farms.     

Protection of pigs against post-weaning multisystemic wasting syndrome by a recombinant adenovirus expressing the capsid protein of porcine circovirus type 2

Post-weaning multisystemic wating syndrome (PMWS) associated with PCV2 was one of the most costly diseases currently faced by the swine industry. In order to develop a vaccine to control this disease, we previously constructed a recombinant adenovirus expressing the capsid of PCV2. Here, we examined the protection of swine against PMWS by the recombinant adenovirus. Eighteen 32-day-old pigs were assigned to three groups each with six. Group 1 was vaccinated subcutaneously with rAd-Cap and boosted 2 weeks later. Thirty-seven days after first vaccination, Groups 1 and 2 were oronasally challenged with virulent PCV2 isolate, 4 and 7 days later, intramuscularly exposed to keyhole limpet hemocyanin (KLH). Group 3 remained unchallenged but with KLH. The results showed that high level of PCV2-specific ELISA antibody and neutralizing antibody could be induced at 37 days after first vaccination. After challenge, pigs in vaccinated group had no clearly clinical signs, although some of them had increased rectal temperatures (>/=40 degrees C) for short time. The pyrexic phase in vaccinated group was significantly lighter than that in challenge-control group (P<0.05). The relative daily weight gain in vaccinated-challenged group was similar to that in empty control group. But it was significantly high compared to the challenge-control group (P<0.05). Mean while the pathological lesions and virema presented in vaccinated group were milder than those in control group. It indicated that the recombinant adenovirus was able to confer significant protection against clinical disease and reduce pathogenic lesions induced by PCV2 challenge, even though it could not provide complete virological protection. The recombinant adenovirus might be an attractive candidate vaccine for preventing the disease associated with PCV2 infection.     

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.     

Detection of neutralizing antibodies in postweaning multisystemic wasting syndrome (PMWS)-affected and non-PMWS-affected pigs

The notion that postweaning multisystemic wasting syndrome (PMWS)-affected pigs develop an impaired humoral response against porcine circovirus type 2 (PCV2) has been reported in several studies. However, little information is available regarding the presence of neutralizing antibodies (NA) in PCV2-infected pigs and their role in the pathogenesis of the disease. The aim of the present work was to further characterize the humoral response, and in particular the production of NA, in pigs with different PCV2-infection status. Seventy-two conventional pigs from different farms were classified into three groups based on PCV2 infection and clinico-pathological status, namely: PCV2-negative, non-PMWS PCV2-positive and PMWS-affected animals. In addition, 9-week old pigs from an experimental infection (6 controls and 14 PCV2-inoculated pigs) were also studied. NA and total PCV2 antibodies (TA) as well as viral load in serum were determined and correlated with the clinico-pathological status of pigs. Results indicated that PMWS-affected pigs had lower NA titres, if any, than healthy animals. NA titres were also inversely correlated with PCV2 load in serum. NA and TA titres were positively correlated; however, correlation differed among infection status, being lower in PCV2-positive pigs. Also, the diagnostic performance of each test was evaluated, indicating that the combination of viral neutralization and quantitative PCR in serum was useful to discard PMWS (specificity 92%). In experimentally infected animals, the evolution of NA paralleled the course TA, although a slight delay in NA production was seen in some animals. The increase of NA coincided with the drop in viral load. Results from this work further support that PMWS-affected pigs show an impaired humoral immune response and, particularly, an inefficient NA response against PCV2.     

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.