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…     

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.     

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.     

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.     

Porcine circovirus induces B lymphocyte depletion in pigs with wasting disease syndrome

To disclose the mechanism of cellular injury following porcine circovirus (PCV) infection, 12 pigs were examined by the terminal deoxynucleotidyl transferase-mediated dUTP-nick end labeling (TUNEL) method and immunohistochemistry. Histologically, the lymphoid tissues were characterized by marked apoptosis of lymphocytes, lymphocyte depletion, and macrophages and giant cells containing numerous inclusion bodies with or without apoptotic bodies. Immunohistochemically, there were many lysozyme-positive macrophages in the lymphoid follicles, while the number of CD79a-positive B lymphocytes was scanty. Apoptotic cells, which were proved to be TUNEL positive, revealed CD79a positivity. Although detectable mainly in the cytoplasm of macrophages, PCV antigens were found also in the nuclei of macrophages and apoptotic lymphocytes. Ultrastructurally, the presence of PCV virions was confirmed in apoptotic bodies phagocytosed by macrophages. These findings suggested that lymphocyte depletion with apoptotic death of B lymphocytes was caused by PCV, and that some of the inclusion bodies were phagolysosomes derived from the apoptosis. Thus, PCV may trigger the development of wasting disease syndrome by producing an immunocompromised state in pigs.     

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.     

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.     

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.     

Porcine circovirus type 2 infection before and during an outbreak of postweaning multisystemic wasting syndrome on a pig farm in the UK

The presence of porcine circovirus type 2 (PCV-2) and other pathogens before and during an outbreak of postweaning multisystemic wasting syndrome (PWMS) in pigs is evaluated in this study. At the time of the outbreak on a large commercial pig farm in the UK, serum samples and data were collected in two independent on-going research projects, one in weaned pigs and the other in sows. Serum samples of growing pigs and sows were PCV-2-antibody and PCR positive before and during the PMWS outbreak. Upon sequencing, PCV-2 isolates collected before the outbreak were identified as PCV-2a, and isolates collected during the outbreak were identified as PCV-2b, suggesting a shift of PCV-2 genotypes present on the farm. Pigs in the weaner study were from sows originating from different breeders and an association of sow origin and PCV-2 serostatus in offspring was found. Further, pigs had higher odds to be PCV-2 antigen positive if the sow was PCV-2 antibody positive around farrowing, the sow was of higher parity, and were less likely to test antigen positive if the sow was sourced from a particular breeder. The findings of this study highlight the potential role of the immune status of the sow on the occurrence of PMWS.     

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.     

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.     

Muco-cutaneous candidiasis in two pigs with postweaning multisystemic wasting syndrome

In two distinct commercial swine herds, poor weight gain and an increased number of animals showing wasting were observed among nursery and growing pigs. Cases of postweaning multisystemic wasting syndrome (PMWS) and infection with Haemophilus parasuis had been previously diagnosed in these herds. One growing wasted pig from each herd was necropsied and showed enlarged lymph nodes. Pseudomembranous material adhered to the dorsum of the tongue, soft and hard palate in case 1, and in case 2, fibrinous material was seen as whitish plaques on the oesophageal surface with hyperkeratosis of the non-glandular stomach. The main histological lesions in both cases were found in lymphoid tissues with a multifocal accentuated lymphohistiocytic infiltrate, areas of lymphoid depletion and intracytoplasmic inclusions in histiocytic cells in lymph nodes and Payer's patches. Focally, extensive ulceration was found in the stratified pavement epithelium of the tongue with necrosis and necrosuppurative infiltrate in case 1; in case 2, there was ulceration in the stomach with lymphohistiocytic infiltrate in the submucosa and ulceration in the mucosa of the oesophagus associated with yeast cells and pseudo-hyphae. Candida albicans was isolated from the oral cavity lesions. Immunohistochemistry of the lymph nodes was positive for porcine circovirus 2 (PCV2). The association between PMWS and mucocutaneous candidiasis reported here supports the potential immunosuppressive state of PMWS infected pigs.     

免疫抑制是断奶后多系统消耗性综合征的一个特征

研究表明,Ⅱ型猪圆环病毒(PCV2)与许多病症有关,它们统称为猪圆环病毒病(PCVD)。在这些疾病中,在经济上最重要的是断奶后多系统消耗性综合征(PMWS),由于该病能直接引起死亡以及显著提高不可上市猪的比例,所以可造成严重的经济损失(Segales和Domingo,2002)。若干证据表明,免疫抑     

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.