Pig-major acute phase protein and haptoglobin serum concentrations correlate with PCV2 viremia and the clinical course of postweaning multisystemic wasting syndrome

The aim of the present longitudinal study was to assess the evolution of two acute phase proteins (APPs), pig-major acute phase protein (pig-MAP) and haptoglobin (HPT), in serum from pigs that developed postweaning multisystemic wasting syndrome (PMWS) in comparison to healthy and wasted non-PMWS affected pigs. In addition, evidence of infection with other pathogens and its relation with variations in APPs concentrations was also assessed. Fourteen independent batches of 100–154 pigs were monitored from birth to PMWS outbreak occurrence in 11 PMWS affected farms. Pigs displaying PMWS-like signs and age-matched healthy controls were euthanized during the clinical outbreak. PMWS was diagnosed according to internationally accepted criteria and pigs were classified as: (i) PMWS cases, (ii) wasted non-PMWS cases and (iii) healthy pigs. At the moment of PMWS occurrence, pig-MAP and HPT concentration in PMWS affected pigs were higher than in healthy ones (p < 0.0001). No differences in APPs serum concentrations between subclinically PCV2-infected pigs and healthy non-PCV2-infected pigs (based on quantitative PCR on serum results) were detected. Results showed a significant correlation between PCV2 loads and both pig-MAP (R = 0.487–0.602, p < 0.0001) and HPT (R = 0.326–0.550, p < 0.05–0.0001) concentrations in serum of PMWS affected pigs, indicating that the acute phase response in PMWS affected pigs occurred concomitantly to PCV2 viremia. No other pathogen, apart from PCV2, was consistently related with variations in APPs concentrations. A ROC analysis, made to determine the capacity of discrimination of both APPs between PMWS affected and non-affected pigs, showed higher sensitivity and specificity values using pig-MAP compared to HPT. These results suggest that pig-MAP might be a better indicator of PMWS status than HPT. Moreover, the fact that APR occurred some weeks before the start of clinical signs suggests that APPs could provide valuable prognostic information for PMWS development.     

A proposal on porcine circovirus type 2 (PCV2) genotype definition and their relation with postweaning multisystemic wasting syndrome (PMWS) occurrence

Porcine circovirus type 2 (PCV2) is the essential infectious agent of postweaning multisystemic wasting syndrome (PMWS). Despite first sequencing studies did not find any association between PCV2 sequences and PMWS occurrence, recent works have suggested the opposite. In the present study, 87 open reading frame 2 (ORF2) sequences obtained from pigs with different clinical conditions and coming from farms with different PMWS status were analyzed. Results further confirmed the existence of two genogroups and the definition of two PCV2 genotypes (1 and 2) is proposed. All sequences included in genotype 1 came from pigs from PMWS affected farms, while all sequences obtained from non-PMWS affected farms corresponded to genotype 2. Moreover, infection of single pigs from PMWS affected farms harbouring both genotypes is described. Present results suggest that PCV2 genotype 1 may potentially be more pathogenic than PCV2 genotype 2.     

Quantification of porcine circovirus type 2 (PCV2) DNA in serum and tonsillar, nasal, tracheo-bronchial, urinary and faecal swabs of pigs with and without postweaning multisystemic wasting syndrome (PMWS)

The present study focused on PCV2 quantification by TaqMan PCR in nasal (n=99), tonsillar (n=108), tracheo-bronchial (n=72), urinary (n=91) and faecal (n=42) swabs, as well as in serum (n=57), from a total of 146 pigs received at the Pathological Diagnostic Service at the Veterinary School of Barcelona (Spain). Animals were classified into three categories based on histopathological and in situ hybridisation (ISH) results: PMWS affected pigs (Group A, n=42), PCV2 subclinically infected pigs (Group B, n=29), and non-PMWS with PCV2 ISH negative pigs (Group C, n=75). Overall, tracheo-bronchial swabs had the higher PCV2 load followed by serum, tonsillar, nasal, faecal and, finally, urinary swabs. PCV2 genome was also detected in different proportions in all three categories of pigs; in all tested sites, viral load means were significantly higher (P0.05) were observed among tested specimens when age-groups (pigs younger than 1.5 months, and equal or older than 1.5 months of age) were compared. In summary, PCV2 is presumably excreted through respiratory (nasal and tracheo-bronchial) and oral (tonsillar) secretions, urine and faeces of both PMWS and non-PMWS affected pigs, with higher viral loads being associated with the presence of PMWS lesions.     

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.     

免疫刺激商品断奶仔猪复制多系统衰竭综合征(PMWS)

猪圆环病毒2型（PCV2）是引起PMWS的必需病原,与其他病原混合感染或受到外界刺激时表现PMWS临床症状。本试验将16头商品化断奶仔猪（32日龄）随机分为4组（每组4头）,即对照组、钥匙孔血蓝蛋白刺激组、PCV2攻毒组和PCV2攻毒后钥匙孔血蓝蛋白刺激组,用上海某猪场分离株PCV2-SH、钥匙孔血蓝蛋白（KLH）反复刺激断奶仔猪以复制PMWS。其中对照组、钥匙孔血蓝蛋白刺激组未出现症状;PCV2攻毒组症状较轻,出现增重缓慢,伴有短暂的体温升高;而PCV2攻毒后钥匙孔血蓝蛋白刺激组出现明显的临床症状,2头猪在攻毒后第11天濒临死亡,其中1头在第12天死亡,攻毒猪宰杀后脏器出现明显的病理变化。PCV2攻毒组和PCV2攻毒后钥匙孔血蓝蛋白刺激组于攻毒后第4天出现病毒血症,宰杀后肺脏、淋巴结均检测到PCV2的DNA。以上结果说明,PCV2-SH感染结合免疫刺激可以引起商品化仔猪发生PMWS,为PCV2致病机理和免疫学研究提供了动物发病模型。     

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.     

Examination for a viral co-factor in postweaning multisystemic wasting syndrome (PMWS)

In order to test the hypothesis that a putative co-factor for the development of postweaning multisystemic wasting syndrome (PMWS) in pigs could be of viral origin, we performed extensive virological examinations on organ material from pigs diagnosed with PMWS originating from within a Danish PMWS-transmission study. Virus isolation attempts were carried out on a large panel of different cell types including primary pig kidney cells and lung macrophages, primary rabbit kidney cells and seven established cell lines (MARC-145, ST117, PK15, BHK21, HeLa, Vero, and MDCK). Although these represent cells with susceptibility to a wide range of known viruses, the results did not provide evidence for a specific virus other than PCV2 contributing to the development of PMWS. Furthermore, in order to test whether specific genotypes of PCV2 may trigger the switch from PCV2 infection to clinical disease, we compared complete DNA genome sequences of PCV2 derived from PMWS-positive as well as PMWS-negative pigs. On the basis of the DNA sequences, the PCV2 isolates were divided into two groups. Group 1 consisting of one isolate originating from a herd unaffected by PMWS, with group 2 consisting of nine isolates originating from four PMWS-affected herds, four PMWS-positive pigs plus one unaffected herd. The PCV2 genomes from the two groups showed 95.5% identity. Alignment analyses of the sequences encoding the replicase and capsid protein from group 1 and group 2 PCV2 isolates showed two amino acid differences encoded in the replicase protein, while 19 amino acid differences were predicted among the capsid protein sequences. The PCV2 DNA sequence analysis supports recent observations from studies in USA as well as Europe, which suggest that strain variations may influence the clinical outcome of PCV2 infection.     

The detection of porcine circovirus in the Australian pig herd

OBJECTIVE: To determine if porcine circovirus (PCV) type 1 (PCV1) or type 2 (PCV2) is present in the Australian pig herd, to conduct preliminary genetic characterisation of any viruses detected, and to determine if there is any obvious virological reason why post-weaning multisystemic wasting disease (PMWS), associated with PCV infection in other countries, has not been detected in Australia. DESIGN: Serum samples were collected from 14 randomly selected pig farms in Western Australia and used for detection of PCV antibody. Additional samples from one farm were obtained at 2-week intervals from pigs between 2 and 12 weeks of age to detect any age-associated variations in prevalence of infection. Veterinary practitioners from four Australian states submitted tissues of dead or unthrifty weaned pigs, and these were examined for evidence of PCV1 and PCV2 infection. PROCEDURE: Sera were tested for antibody to PCV using an indirect immunofluorescence assay (IFA). Tissues were tested for PCV1 and PCV2 genomic material using a multiplex PCR. RESULTS: PCV antibody was detected in approximately 30% of Western Australian pigs tested. PCV1 DNA was detected in tissue samples from Western Australia, South Australia and New South Wales and PCV2 DNA was detected in tissue samples from Western Australia, New South Wales and Queensland. Sequence analysis of the PCR products indicated the PCV1 and PCV2 present in Australia were very similar to strains in other countries where PMWS is endemic. CONCLUSION: Both PCV1 and PCV2 are present in Australia and the viruses present appear similar to those in countries with PMWS. The absence of PCV2-associated PMWS in Australia may be due to absence of essential secondary factors required for PCV2 to produce PMWS.     

Reproduction of postweaning multisystemic wasting syndrome in pigs by prenatal porcine circovirus 2 infection and postnatal porcine parvovirus infection or immunostimulation

Postweaning multisystemic wasting syndrome (PMWS) was reproduced in prenatally porcine circovirus 2 (PCV2)-infected pigs by either postnatal infection with porcine parvovirus (PPV) or by immunostimulation. Twenty-four randomly selected piglets from 3 sows, which had been experimentally infected during gestation with PCV2, were randomly divided into 3 groups; group 1 (prenatal PCV2 infection, with postnatal PPV infection), group 2 (prenatal PCV2 infection, with postnatal keyhole limpet hemocyanin, emulsified in incomplete Freund's adjuvant [KLH/ICFA] injection), and group 3 (prenatal PCV2 infection only). Twenty-four randomly selected piglets from 3 uninfected sows were randomly divided into 3 groups; group 4 (no prenatal infection, with postnatal PCV2 and PPV infection), group 5 (no prenatal infection, with postnatal PCV2 infection), and group 6 (negative control pigs). Body weight in negative control pigs (group 6) was increased significantly compared with pigs in groups 1, 2, and 4 at 49, 52, 56, 59, and 63 days of age. The granulomatous inflammatory reaction and lymphoid depletion that are typical lesions in pigs with PMWS were observed in the lymph node of piglets in groups 1, 2, and 4 at 63 days of age. Pigs in group 3 had significantly fewer PCV2-positive cells than those from groups 1, 2, 4, or 5. When the prenatally PCV2-infected pigs were infected with PPV or injected with immunostimulant in the postnatal period, they developed PMWS. Thus, factors that potentiate the progression of prenatal PCV2 infection to PMWS are postnatal infection with PPV or immune stimulation.     

吉林部分地区TTSuVs与PCV2混合感染情况调查及其与PMWS相关性分析

为了解吉林地区猪细环病毒(TTSuVs)与II型猪圆环病毒(PCV2)混合感染情况,分析TTSuVs感染与仔猪多系统衰竭征(PMWS)的相关性。试验通过PCR技术对2019年收集到的吉林部分地区的10家规模化猪场130份血清样本进行检测;并应用本实验已建立的PCV2、TTSuVs实时荧光定量PCR检测方法,对PCV2阳性样品进行病毒载量的分析,区分PMWS病猪与PCV2亚临床感染猪,比较PMWS病猪与PCV2亚临床感染猪中TTSuVs的载量。结果显示:TTSuV1感染率为38.46%;TTSuV2感染率为57.69%;PCV2感染率为46.15%;TTSuV1与TTSuV2的混合感染率为31.54%;TTSuV1与PCV2的混合感染率为32.30%;TTSuV2与PCV2的混合感染率为44.62%;三种病毒的混合感染率为22.30%。且PMWS病猪血清中TTSuV2载量明显高于PCV2亚临床感染猪(P<0.01)。结果表明,TTSuV2载量与PMWS病的发生存在一定程度的相关性。     

The presence of co-infections in pigs with clinical signs of PMWS in The Netherlands: a case-control study

In this study, 60 pigs with clinical signs of post-weaning multisystemic wasting syndrome (PMWS) from 20 different pig herds and 180 control pigs (without clinical signs of PMWS) were examined to get more insights into the frequencies of porcine circovirus 2 infections and the presence of co-infections in pigs with and without clinical signs of PMWS in the Netherlands. Porcine circovirus type 2 was detected in 100% of the pigs with clinical signs of PMWS by virus isolation and/or PCR and in 50% of the pigs from PMWS-free herds. There was an association between the levels of infectious PCV2 and/or PCV2 DNA load and the severity of clinical signs as described for PMWS. A high variation in PCV2 antibody titres was found in the clinically affected pigs, and 27% of these pigs did not mount PCV2 antibody titres higher than 1:200. A concurrent infection of PCV2 and porcine reproductive and respiratory syndrome virus (PRRSV) was found in at least 83% of the pigs with clinical signs of PMWS and in 35% of the pigs from PMWS-free herds. Co-infections of European- and American-type PRRSV were detected only in PMWS herds and in one control herd with a history of PMWS clinical signs.     

PCR detection of porcine circovirus type 2 (PCV2) DNA in blood, tonsillar and faecal swabs from experimentally infected pigs

PCV2 infection is now recognized as the major factor in the development of post-weaning multisystemic wasting syndrome (PMWS). In this study we evaluated the use of PCR to detect the presence of PCV2 DNA in blood, faecal and tonsillar swabs collected from 12 pigs experimentally infected with PCV2 and sampled at selected time points post-infection. The PCR results were evaluated together with the presence of PMWS typical histopathological lesions and the presence of PCV2 antigen. PCV2 DNA was present in the blood of all 12 infected pigs at the end of the experiment and faecal and tonsillar swabs of 11 of the 12 pigs. The rate of PCR-positive serum and plasma samples was significantly higher in four pigs that showed virological and pathological evidence of PMWS, than in infected pigs without evidence of disease. In conclusion this study confirms that PCR cannot substitute for the traditional methods used for diagnosis of PMWS, however, PCR amplification of PCV2 DNA from serum or plasma could be a useful tool to support an early diagnosis of PMWS in live animals.     

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.     

Mycoplasma hyopneumoniae bacterins and porcine circovirus type 2 (PCV2) infection: induction of postweaning multisystemic wasting syndrome (PMWS) in the gnotobiotic swine model of PCV2-associated disease

Groups (5 to 15 per group) of gnotobiotic swine were infected oronasally with porcine circovirus type 2 (PCV2) at 3 days of age and then given 1 of 6 different commercial Mycoplasma hyopneumoniae (M. hyopneumoniae) bacterins as either a single dose (7 d of age, 1 application products) or 2 doses (7 and 21 d of age, 2 application product). Control groups received PCV2 alone (n = 9) or were infected with PCV2 and immunized twice with keyhole limpet hemocyanin (KLH) emulsified in incomplete Freund's adjuvant (ICFA) (n = 7). Five of 7 (71%) PCV2-infected piglets immunized with KLH/ICFA developed mild or overt PMWS, whereas none of 9 piglets infected with PCV2 alone developed PMWS. Five of 12 (42%) piglets vaccinated with a commercial bacterin containing mineral oil adjuvant developed PMWS following vaccination. None of the PCV2-infected piglets in the other bacterin-vaccinated groups developed PMWS in this model of PCV2-associated disease. This difference in prevalence of PMWS in piglets given the mineral oil-adjuvanted M. hyopneumoniae bacterin and the other M. hyopneumoniae bacterin vaccination groups was statistically significant (P < 0.05).     

Comparative serologic and virologic study of commercial swine herds with and without postweaning multisystemic wasting syndrome

A comparative serologic and virologic study was performed in pigs from 5 herds with postweaning multisystemic wasting syndrome (PMWS) and 2 herds without PMWS in Quebec. In each herd, 60 blood samples were collected at 4-wk intervals from pigs from 3 to 23 wk of age. The serum was evaluated for the presence of antibodies to porcine circovirus type 2 (PCV2) and porcine reproductive and respiratory syndrome virus (PRRSV), as well as for the presence of nucleic acid of PCV2, PRRSV, and porcine parvovirus (PPV), by means of the polymerase chain reaction (PCR). Serologic profiles for PCV2 were very similar in 6 of the 7 herds, including the 2 without PMWS, and were characterized by a gradual decrease in antibody titres from 3 until 11 wk of age, followed by seroconversion at 15 wk, and high PCV2 antibody titres thereafter in all pigs. Only starting at 11 to 15 wk of age could PCV2 viremia be detected, except in 1 herd, in which clinical signs were observed at 6 to 7 wk of age. A PCV2 viremia could be detected within the same pigs for a minimum of 8 wk, and the virus could still be detected in 41% of the serum samples obtained at 23 wk of age. The antibody level did not appear to influence the occurrence of disease, since titres were similar in pigs in the herds with or without PMWS. Infection with PRRSV, as demonstrated by PCR and seroconversion, preceded that of PCV2 by at least 1 mo in both types of herd. Both PRRSV and PCV2 were detected in some pigs in 5 of the 7 herds, including 1 herd without PMWS. Porcine parvovirus could be detected in serum by PCR in 2 herds with PMWS after the onset of clinical signs and also in 1 herd without PMWS. Genomic analysis of PCV2 strains identified in the herds without PMWS indicated complete or very high homology (99.4% to 100%) with the PCV2 strains identified in 4 herds with PMWS. In our field study, the triggering of PMWS in the herds could not be linked to coinfection with either PRRSV or PPV or to the use of a specific immunostimulant, such as vaccines, or to particular genomic differences between the PCV2 strains identified.     

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.     

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.     

An exploratory study on risk factors for postweaning multisystemic wasting syndrome (PMWS) in Spain

An exploratory case-control study was carried out in Spain in 2002/2003, involving 62 pig farms of different production systems to assess risk factors that, in association with PCV2 infection, induce postweaning multisystemic wasting syndrome (PMWS) expression. To achieve this objective two groups of farms selected according to their PMWS status were compared: "cases" (farms with clinical PMWS, n = 32) and "controls" (farms without clinical PMWS, n = 30). A filled-in questionnaire and 45 blood samples (15 sows, and two groups of 15 pigs of 12 and 20 weeks of age, respectively) were obtained from each farm. Additionally, two to three diseased pigs were necropsied and relevant tissues to diagnose PMWS collected when PMWS was clinically suspected ("case" farms). A statistical analysis to compare "case" versus "control" farms was performed with the variables obtained from the questionnaire (191 variables) and the serologic test results (20 variables). Data were analysed using conditional logistic regression with a nested n:m matched design taking into account the farm size. Three variables were found significant in the final model: two related to vaccination scheme and one to PCV2 seroprevalence in growing pigs. Vaccination of gilts against PRRSV increased the odds of PMWS expression and vaccination of sows against atrophic rhinitis was related to decreased odds of the disease; however, the possibility that those two factors could be spurious effects (due to the small sample size) or confounding variables cannot be ruled out. On the other hand, a higher prevalence of antibodies to PCV2 at 12 weeks of age was observed in pigs from "case" farms than in pigs from "control" farms. This result suggests that an earlier infection with PCV2 might be a risk factor for PMWS expression.     

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.     

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.