Comparison of a commercial ELISA and an immunoperoxidase monolayer assay to detect antibodies directed against porcine respiratory and reproductive syndrome virus

A commercially available enzyme-linked immunosorbent assay (ELISA) for the detection of antibodies against porcine respiratory and reproductive syndrome virus (PRRSV) was compared to an immunoperoxidase monolayer assay (IPMA). Serum samples used were collected from pigs experimentally infected with either the American or European antigenic type of PRRSV, and also from piglets born to sows that had been experimentally infected with the European antigenic type of PRRSV. In addition, three sets of European field sera (n = 275, n = 68, n = 349) were tested and evaluated using the IPMA as the gold standard. Results showed that both the IPMA and the ELISA were able to detect antibodies against the two antigenic types of PRRSV. When sera of experimentally infected pigs were tested, the IPMA with homologous antigen detected antibodies 2 to 3 days earlier than the ELISA, and was more sensitive in detecting maternal antibodies. The ELISA was slightly more sensitive for detecting antibodies against the American type than for the European type. When sets of field sera were tested, the relative sensitivity of the ELISA ranged between 0.68 and 0.91, and the relative specificity ranged between 0.75 and 0.97. However, in two of these sets (n = 275, n = 349) we determined that a decrease of the threshold value of ELISA (from 0.4 to 0.3) increased sensitivity without loss of specificity. We concluded that the ELISA is an easy, quick and reliable test to diagnose PRRSV infection in swine herds