Retrospective study on porcine circovirus type 2 infection in pigs from 1985 to 1997 in Spain.

A retrospective survey was performed to detect lesions of Postweaning multisystemic wasting syndrome (PMWS) and nucleic acid of porcine circovirus type 2 (PCV2) in archived formalin-fixed, paraffin-embedded tissues from 189 pigs, and antibodies to this virus in sera of 388 pigs from the Spanish livestock between the years 1985 and 1997. PCV2 nucleic acid was detected by in situ hybridization (ISH) in tissues from 78 of 189 (41.3%) examined pigs. Variable amount of viral genome was detected in association with slight to severe microscopic lymphoid lesions consisting of lymphocyte depletion and histiocytic infiltration. The first positive case of PMWS with typical lesions and ISH positive corresponded to a pig necropsied in 1986. Two hundred and eighty-two of 388 (72.7%) sera were positive by immunoperoxidase monolayer assay. Serological and pathological data of the present study indicate that PCV2 was a enzootic infection in Spain since 1985, suggesting that the introduction of this virus in the livestock occurred previously.

Clinical and pathological observations on pigs with postweaning multisystemic wasting syndrome.

The aim of this work was to characterise the lesions and agents present in clinically normal and clinically affected pigs on a farm during an outbreak of postweaning multisystemic wasting syndrome (PMWS), and to evaluate the diagnostic techniques for detecting porcine circovirus type 2 (PCV-2) and other microorganisms. Four pigs in the early stage and 11 pigs in the late stage of the disease, and eight clinically normal pigs were necropsied. Samples of lymphoid tissue and serum were also obtained from 12 slaughter pigs from the same farm. The tissues were examined histopathologically, and in situ hybridisation, serology and PCR were used to detect porcine circovirus type 1 (PCV-1) and/or PCV-2 in tissues and/or sera. The presence of porcine reproductive and respiratory syndrome virus (PRRSV), Aujeszky's disease virus (ADV) and porcine parvovirus (PPV) were also investigated. Characteristic microscopical lesions of PMWS were observed in the lymphoid tissues of the pigs in all three necropsied groups; the lesions were most common and severe in the pigs in the early stage of the disease, less so in the pigs in the late stage of the disease, and least in the clinically normal pigs. PCV-2 infection was detected in all the necropsied pigs by in situ hybridisation and PCR. Only three pigs had the PCV-1 genome in serum or lymph node tissue. In contrast, the slaughter pigs had no microscopical lesions and no PCV-2 nucleic acid in their serum or tissues, and only one of them had the pCV-1 genome in its serum. Immunohistochemical, serological and PCR studies revealed that PRRSV and ADV were also present on the farm during the outbreak.

Identification of porcine circovirus in tissues of pigs with porcine dermatitis and nephropathy syndrome.

Thirty-three pigs affected by porcine dermatitis and nephropathy syndrome, 30 from Spain and three from the USA, were investigated in order to detect porcine circovirus (PCV) in their tissues. A standard in situ hybridisation technique using a specific DNA 317-bp probe based on a well-conserved sequence of PCV (which recognises both PCV-1 and PCV-2) was applied to formalin-fixed, paraffin-embedded tissues. Twenty-eight of the 30 Spanish pigs and all three American pigs had PCV in at least one tissue. Viral nucleic acid was detected mainly in lymphoid organs, and especially the lymph nodes. The viral genome was also found, in order of decreasing quantity, in Peyer's patches, tonsil, lung, spleen, kidney, liver, and skin. Viral nucleic acid was located mainly within the cytoplasm of monocyte/macrophage lineage cells, including follicular dendritic cells, macrophages, histiocytes and Kupffer cells. No viral nucleic acid was found in damaged glomeruli or arteriolar walls. In frozen samples available from three Spanish pigs, the virus was identified as type 2 by using the polymerase chain reaction and restriction fragment length polymorphism. Most of the pigs from which serum was available were seropositive against porcine respiratory and reproductive syndrome virus (PRRSV), and PRRSV antigen was detected in the lung of two of the Spanish pigs. These results suggested that PCV is present in tissues of almost all pigs affected by PDNS, and PCV has to be considered as a possible agent involved in the pathogenesis of the syndrome.

Pathological, immunohistochemical, and in-situ hybridization studies of natural cases of postweaning multisystemic wasting syndrome (PMWS) in pigs.

Fifteen pigs from five farms on which there had been a previous clinical and histopathological diagnosis of postweaning multisystemic wasting syndrome (PMWS) were investigated. At necropsy, enlargement of lymph nodes was the most obvious lesion; other lesions were non-collapsed lungs, ulceration of the gastric pars oesophagica, and cranioventral pulmonary consolidation. Microscopical lesions attributable to PMWS were found in lymphoid organs (including lymph nodes, tonsil, Peyer's patches and spleen), liver, kidney and lungs. Varying degrees of lymphocellular depletion, affecting both lymphoid follicles and parafollicular zones, and progressive multifocal to diffuse infiltration of lymphoid tissue by large histiocytic cells were the characteristic lesions. Syncytial cells were seen frequently, especially in lymphoid organs. A prominent finding was the presence of sharply demarcated, spherical, basophilic, cytoplasmic inclusions in histiocytic cells. The lymphoid lesions were suggestive of immunosuppression. Non-lymphoid lesions included interstitial pneumonia, periportal mononuclear inflammatory infiltration of the liver in varying degrees, and interstitial nephritis. Porcine circovirus (PCV) antigen and nucleic acid were regularly found in lymphoid organs, lung, liver and, to a lesser degree, kidney. Target cells for PCV replication included monocyte/macrophage lineage and antigen-presenting cells. To a lesser extent, epithelial cells such as renal tubular, bronchial and bronchiolar cells, endothelial cells, hepatocytes and lymphocytes were also labelled. One pig did not show PCV nucleic acid; sequence differences among different viral isolates are discussed as the probable cause of this lack of labelling by the in-situ hybridization PCV-specific probe.