A comparison of in situ hybridization and immunohistochemistry for the detection of a new porcine circovirus in formalin-fixed tissues from pigs with post-weaning multisystemic wasting syndrome (PMWS).

Post-weaning multisystemic wasting syndrome (PMWS) is a recently identified condition affecting pigs in North America and Europe. Porcine circovirus antigen and nucleic acid have been demonstrated associated with lesions, and a new porcine circovirus designated PCV2 has been recovered from tissues of these animals. In this study, in situ hybridisation and immunohistochemical protocols were developed, optimized and compared for their relative sensitivity in detecting PCV2 antigens and nucleic acid in tissues from cases of PMWS that had been fixed for up to 6 months in formalin. For both immunohistochemistry and in situ hybridization, an increase in specific signal was observed following increased exposure to both protease XIV and proteinase K. Maximum signal and minimal loss of tissue morphology was seen after 40 min treatment with protease XIV (0.5 mg/ml). After optimisation, a comparison of these techniques on sequential sections demonstrated that both techniques successfully detected antigen or nucleic acid in all of the tissues examined. More positive cells, with increased signal intensity, were detected following immunohistochemistry.