Profiles of seroconversion to porcine circovirus type 2 in herds affected and not affected by postweaning multisystemic wasting syndrome

The aim of the present study was to explore the usefulness of serological methods in the diagnosis of postweaning multisystemic wasting syndrome (PMWS). The study was carried out in 4 PMWS-affected and 6 control farms. Based on the serological profiles, infection with porcine circovirus type 2 (PCV2) was determined to take place at 3-7 weeks of age in the PMWS-affected and at 3-11 weeks of age in the control farms. To compare the dynamics of seroconversion to PCV2 among farms, cross-sectional serological profiles were normalised in relation to the inferred age of infection. The results indicated that the proportion of seropositive pigs increased significantly slower in the affected herds. The most pronounced difference was observed about 4 weeks after infection, when the proportion of seropositive pigs ranged from 0 to 53.3% and from 70 to 100% in PMWS-affected and control herds, respectively. Mean antibody titres at that age were also significantly lower in the affected farms. These observations suggest a delay in the production of PCV2-specific antibodies and indicate that serological methods may be helpful in identifying herds with a high risk of PMWS.     

猪圆环病毒感染与断奶仔猪多系统衰竭综合征

1974年 ,德国学者 Tischer等 [1 ] 从 PK- 15 (ATCCCCL31)细胞的污染病毒中检出一种形态学上与细小核糖核酸病毒相似的小球形病毒和乳多泡病毒样病毒粒子 ,并于1982年将其命名为猪圆环病毒 (porcine circovirus,PCV) [2 ] 。目前已知 PCV有 PCV- 1和 PCV- 2 2个血清型。PCV- 1来源于 PK- 15细胞 ,为非致病性 PCV(nonpathogenic PCV,np PCV ) [3 ] ;PCV- 2与断奶仔猪多系统衰竭综合征(postweaning m ultisystem ic wasting syndrom e,PMWS)密切相关 ,又称 PMWS相关 PCV[3 ] (PMWS- associated PCV,pmws- PCV)。 PM…     

Survey of porcine circovirus 2 and postweaning multisystemic wasting syndrome in New South Wales piggeries

OBJECTIVE: To determine if postweaning multisystemic wasting syndrome (PMWS) is occurring in the New South Wales pig population and to determine the current and past seroprevalence of porcine circovirus 2 (PCV2). DESIGN: Pig veterinarians were contacted seeking submission of tissues from animals with clinical signs suggestive of PMWS. Samples were also accepted from suspected cases of porcine dermatitis and nephropathy syndrome (PDNS). Serological studies were also undertaken on archival sera and sera submitted during the study. PROCEDURE: Histopathological examination was undertaken on all tissues submitted. The presence of PCV2 was determined by immunohistochemistry. Sera were tested for PCV2 using a commercial enzyme linked immunosorbent assay kit modified for testing of serum samples. RESULTS: No cases of PMWS were identified during the study. Four cases of PDNS were identified. PCV2 antibody was detected in 80% of archival sera from 1995 and 75.8% from 2001. Seroprevalence in samples tested during 2002-2003 was 87.8%. PCV2 was isolated from tissues of a case of PDNS. CONCLUSION: PCV2 is widespread in the New South Wales pig population and has been since at least 1995. This study describes the first isolation of an Australian PCV2. No cases of PMWS were identified in New South Wales.     

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

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

Immunosuppression in postweaning multisystemic wasting syndrome affected pigs

The present review concentrates on the clinical, pathological and immunological aspects of pigs suffering from PMWS which strongly suggest that PCV2 may be, in particular conditions, a cause of secondary immunodeficiency in pigs. From a clinical point of view, the lack of antibiotic therapy response against the disease, the existence of a litter effect and the concurrence of other disease syndromes and well-known secondary pathogens, such as Pneumocystis carinii, Chlamydia spp. and Aspergillus spp., may account as features of immunosuppression in PMWS. Furthermore, pathologic, immunohistologic and flow cytometric studies also suggest that pigs with PMWS may be immunosuppressed. Lymphocyte depletion of follicular and interfollicular areas together with macrophage infiltration of lymphoid tissues is a unique lesion, which is the basic feature of PMWS affected pigs. These findings are highly correlated with the decrease of circulating B- and T-cells and the diminution of these cell types in lymphoid organs, and with the increase of macrophage/monocytes lineage cells both in peripheral blood and lymphoid tissues in both naturally and experimentally PMWS affected pigs. The altered populations of cells participating in the immune system response both in blood and tissues suggests, at least in those severely PMWS affected pigs, a transient inability of diseased pigs to mount an effective immune response. From these points of view, strong suspicions on the immunosuppressive status of PMWS affected pigs do exist; however, future studies are needed to characterise the exact role of PCV2 on the immune system of pigs affected with PMWS.     

Porcine circovirus type 2 viremia and seroconversion in pigs from a farm affected by postweaning multisystemic wasting syndrome

The aim of the study was to assess the usefulness of real-time PCR and serological methods as indicators of postweaning multisystemic wasting syndrome (PMWS) occurrence. Significantly higher level of porcine circovirus type 2 (PCV2) viral load in serum and significantly lower titre of specific antibodies in PMWS-affected pigs indicated that combination of quantitative PCR and serological methods may support diagnosis of PMWS.     

猪断奶后多系统衰竭综合征诊断方法的系列研究

本研究对猪断奶后多系统衰竭综合征(PMWS)的诊断方法临床症状和病理变化、病毒的分离与鉴定、聚合酶链式反应(PCR)、间接免疫荧光试验(IFA)、间接酶联免疫吸附试验(IELISA)、免疫组织化学试验(IHC)等进行了系列研究,这些方法适用于猪断奶后多系统衰竭综合征的诊断.     

Isolation of circovirus from lesions of pigs with postweaning multisystemic wasting syndrome.

Postweaning multisystemic wasting syndrome (PMWS), an apparently new disease, has been recognized in swine herds in western Canada. Young pigs with this disease have progressive weight loss, tachypnea, dyspnea, and jaundice, accompanied by interstitial pneumonia, lymphadenopathy, hepatitis, and nephritis. We examined more than 400 pigs from more than 70 herds in Alberta, Saskatchewan, and Manitoba with cases of PMWS. A small virus was isolated from a range of tissues from 8 of 8 affected pigs examined. The agent was identified as a circovirus-like virus using electron microscopy, immunohistochemical staining with porcine and rabbit immune serum, and in situ hybridization. Immunohistochemical examination of tissues from more than 100 affected pigs has revealed widespread viral antigen, often contained in circovirus-like inclusion bodies, in lesions from numerous organs. Although Koch's postulates remain to be fulfilled, these results demonstrate a high degree of association between the presence of the circovirus-like virus and PMWS in affected swine.     

Dynamics of porcine circovirus type 2 infection in a herd of pigs with postweaning multisystemic wasting syndrome

OBJECTIVE: To determine the pattern of infection for porcine circovirus type 2 (PCV2) in a herd of pigs with postweaning multisystemic wasting syndrome (PMWS). ANIMALS: 29 sows and 250 pigs. PROCEDURE: Blood samples were collected from all 3-, 7-, and 12-week old pigs and 59 pigs at 28 weeks of age. Pigs that died during the study were necropsied. Porcine parvovirus and PCV2 antibodies were assayed. A polymerase chain reaction (PCR) was used to detect PCV2 genome in serum of selected pigs. RESULTS: The PMWS started when pigs were 8 weeks old, with a prevalence of 30% in 8- to 10-week-old pigs. Eighty-three pigs died during the period between 3 and 12 weeks of age. Microscopic lesions consistent with PMWS were observed, and PCV2 nucleic acid was detected (50 of 68 pigs). Antibodies to PCV2 decreased from 3 to 7 weeks of age, increased at 12 weeks of age, and were maintained until 28 weeks of age. One sow had a positive result for PCR of serum. Nine, 37 and 8 pigs had PCV2 genome in serum obtained at 7, 12, and 28 weeks of age, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Infection with PCV2 coincided with severe clinical signs; however, infected 28-week-old pigs did not have evidence of disease. Immunity declined over time in young pigs. A long duration of PCV2 viremia was apparent in a high percentage of infected pigs, which may affect transmission and persistence of the virus in a herd.     

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.     

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.     

Brain lesions in pigs affected with postweaning multisystemic wasting syndrome.

Anti-porcine circovirus type 2 (anti-PCV2) immunostaining was associated with cerebellar lymphohistiocytic vasculitis combined with hemorrhages (50 pigs) or with lymphohistiocytic meningitis (23 pigs) in pigs naturally affected with postweaning multisystemic wasting syndrome (PMWS). The animals originated from 12 farms in Rio Grande do Sul, Brazil. In total, 456 unthrifty 3- to 5-month-old postweaning pigs confirmed as PMWS cases were necropsied. Although most findings mimicked those extensively reported in PMWS-affected pigs, there were distinctive brain lesions that included multiple hemorrhages in the cerebellar leptomeninges associated with lymphohistiocytic vasculitis and fibrinoid degeneration in vessels of the cerebellum and periventricular areas (69 pigs). These vascular lesions were also seen in conjunction with lymphohistiocytic meningitis (38 additional pigs). PCV2 antigen was immunohistochemically demonstrated in the cytoplasm and nuclei from intralesional perivascular macrophages and endothelial-like cells in brain tissues. Together these findings suggest that these lesions were caused by PCV2.     

Viral wasting syndrome of swine: experimental reproduction of postweaning multisystemic wasting syndrome in gnotobiotic swine by coinfection with porcine circovirus 2 and porcine parvovirus

One-day-old gnotobiotic piglets were inoculated intranasally with in vitro passaged porcine circovirus 1 (PCV-1), PCV-2, and porcine parvovirus (PPV) alone or in combination (PCV-1/PCV-2, PCV-1/PPV, and PCV-2/PPV). Piglets were evaluated for 1) the development of porcine postweaning multisystemic wasting syndrome (PMWS), 2) distribution of viral antigens by immunochemistry, and 3) viremia and the presence of viral DNA in nasal and ocular secretions and feces. All single agent-infected piglets and piglets infected with PCV-1/PCV-2 or PCV-1/PPV were clinically asymptomatic. They were transiently viremic and seroconverted to homologous virus(es). At termination of the study on postinfection day (PID) 35, microscopic lesions were restricted to focal inflammatory cell infiltrates in livers and myocardia. One piglet given PCV-1/PPV was PPV viremic for 2 weeks after infection and had lymphangiectasia of the spiral and descending colon associated with granulomatous inflammation. All four PCV-2/PPV-inoculated piglets developed PMWS, characterized by sudden onset of depression and anorexia, icterus, and submucosal edema. One piglet became moribund on PID 27, and the remaining three piglets were euthanatized between PID 27 and PID 30 because of severe disease. Lymph nodes were small and the livers were mottled. Disseminated angiocentric granulomatous inflammation was present in all tissues examined except the brain. Multiple lightly basophilic intracytoplasmic inclusion bodies were identified in macrophages and histiocytes. PCV-2 antigen was widely distributed within macrophages; PPV antigen was sparse. Hepatocellular necrosis and bile retention were prominent. PCV-2 DNA was identified in ocular, fecal, and nasal secretions. Terminal sera contained antibodies to PPV (4/4) and PCV-2 (3/ 4). Production of PMWS in gnotobiotic swine appears to require PCV-2 and additional infectious agents such as PPV for full disease expression in gnotobiotic piglets.     

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.     

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.     

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.     

Experimental reproduction of postweaning multisystemic wasting syndrome in pigs by dual infection with Mycoplasma hyopneumoniae and porcine circovirus type 2

The objectives of this study were to investigate the interactions between Mycoplasma hyopneumoniae and porcine circovirus type 2 (PCV2) and to establish a model for studying the pathogenesis of and testing intervention strategies for the control of PCV2-associated porcine respiratory disease complex (PRDC). Sixty-seven pigs were randomly assigned to four groups. Group 1 (n=17) pigs served as controls, group 2 (n=17) pigs were inoculated with M. hyopneumoniae, group 3 (n=17) pigs were dual infected with M. hyopneumoniae and PCV2, and group 4 (n=16) pigs were inoculated with PCV2. Pigs were inoculated intratracheally with M. hyopneumoniae at 4 weeks of age followed by intranasal inoculation with PCV2 at 6 weeks of age. Dual-infected pigs had moderate dyspnea, lethargy, and reduced weight gain. The overall severity of macroscopic lung lesions, PCV2-associated microscopic lesions in lung and lymphoid tissues, and the amount of PCV2-antigen associated with these lesions were significantly (P <0.05) higher in dual-infected pigs compared with all other groups. Four of 17 (23.5%) dual-infected pigs had decreased growth rate and severe lymphoid depletion and granulomatous lymphadenitis associated with high amounts of PCV2-antigen consistent with postweaning multisystemic wasting syndrome (PMWS). PCV2-antigen in lung tissue was most often associated with M. hyopneumoniae-induced peribronchial lymphoid hyperplasia, suggesting that this is an important site for PCV2 replication in the lung. This study indicates that M. hyopneumoniae potentiates the severity of PCV2-associated lung and lymphoid lesions, increases the amount and prolongs the presence of PCV2-antigen, and increases the incidence of PMWS in pigs.     

Use of a polymerase chain reaction assay and an ELISA to monitor porcine circovirus type 2 infection in pigs from farms with and without postweaning multisystemic wasting syndrome

OBJECTIVE: To determine whether correlations exist between viremia with porcine circovirus type 2 (PCV2) and serum antibody profiles and between detection of PCV2 in nasal cavities and viremia of pigs from farms with and without postweaning multisystemic wasting syndrome (PMWS). ANIMALS: 495 pigs, ranging from the late nursery stage to the early grower-finisher stage of production. PROCEDURE: Serum antibodies to PCV2 were studied with an ELISA that detects the ORF2 viral protein. Nasal swab specimens and serum samples were tested with a PCV2-specific PCR assay. RESULTS: PCV2 DNA and serum antibodies to PCV2 were detected in pigs from all farms, although in different proportions. Overall, PCV2 DNA was detected in greater percentages in serum samples and nasal swab specimens of pigs from farms with PMWS. Although viral DNA was detected in both serum samples and nasal swab specimens, PCV2 detection in nasal swab specimens was higher than in serum samples of pigs from all farms. Serum antibodies to PCV2 were detected in a greater percentage of pigs from farms with PMWS, compared with farms without PMWS. CONCLUSIONS AND CLINICAL RELEVANCE: A high prevalence of PCV2 infection was found in pigs from farms with and without PMWS. Besides the presence of PCV2, unknown additional factors may be necessary to induce the full expression of PMWS.     

Porcine postweaning multisystemic wasting syndrome in Korean pig: detection of porcine circovirus 2 infection by immunohistochemistry and polymerase chain reaction.

This report describes the first diagnosis of porcine circovirus (PCV) infection in weaned pigs with postweaning multisystemic wasting syndrome in Korea by immunohistochemistry and polymerase chain reaction. The most unique lesions were multifocal granulomatous inflammation affecting lymph nodes, liver, and spleen, characterized by infiltrates of epithelioid macrophages and multinucleated giant cells. Circoviral antigen was detected in formalin-fixed sections and was usually present in large, round, dendritic cells in the white pulp of spleen and remnants of follicles in lymph nodes. Lymphoid follicles in the tonsils also contained PCV antigen. A 530-bp DNA fragment of circovirus was successfully amplified from all tested lymph nodes, liver, and spleen.