Comparative serology of porcine reproductive and respiratory syndrome in eight European laboratories, using immunoperoxidase monolayer assay and enzyme-linked immunosorbent assay.

The members of a European Community Concerted Action participated in a study to compare in-house and commercial tests for the serodiagnosis of porcine reproductive and respiratory syndrome (PRRS). These tests included the immunoperoxidase monolayer assay (IPMA) and enzyme-linked immunosorbent assay (ELISA). The trials involved assays on experimentally-produced reference sera, a blind trial of sera of known status, and a comparative study of negative and 'problem' field sera. The results showed a high level of agreement among IPMA tests used in the participating laboratories at the herd level, with only minor inconsistencies in testing early post-infection sera. A blocking ELISA, used in experimental work by one laboratory, was almost as sensitive as IPMA in assays of reference and validation trial sera. Commercial ELISAs were generally less sensitive than IPMA when used to assay ten-day post-infection sera. Discrepant results among certain field sera are likely to be due to antigenic variation among PRRS viruses in Europe. This may lead to increasing instances of misdiagnosis using tests which rely solely on test antigens derived from single PRRS virus isolates.