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 o ther microorganisms. Four pigs in the early stage and 11 pigs in the late s tage of the disease, and eight clinically normal pigs were necropsied. Samp les of lymphoid tissue and serum were also obtained from 12 slaughter pigs from the same farm. The tissues were examined histopathologically, and in s itu 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 vi rus (ADV) and porcine parvovirus (PPV) were also investigated. Characterist ic microscopical lesions of PMWS were observed in the lymphoid tissues of t he pigs in all three necropsied groups; the lesions were most common and se vere 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 hybridisati on and PCR. only three pigs had the PCV-1 genome in serum or lymph node tis sue. In contrast, the slaughter pigs had no microscopical lesions and no PC V-2 nucleic acid in their serum or tissues, and only one of them had the PC V-1 genome in its serum. Immunohistochemical, serological and PCR studies r evealed that PRRSV and ADV were also present on the farm during the outbrea k.