DETECTION OF CHALLENGE VIRUS IN FETAL TISSUES BY NESTED PCR AS A TESTOF THE POTENCY OF A PORCINE PARVOVIRUS VACCINE

To estimate the potency of a porcine parvovirus (PPV) vaccine, three v accinated and three nonvaccinated pregnant gilts were infected with PP V and the distribution of the virus was studied in the tissues of thei r 51 fetuses. Virus detection was attempted using haemagglutination (H A) and immunofluorescence (IF) assays, as well as by standard (single) and nested polymerase chain reactions (PCR. None of the detection met hods yielded positive results when used to test for the presence of vi rus in suspensions of organs from the fetuses from the vaccinated gilt s. How ever, the vit us was detected in the fetuses from non-vaccinate d gilts as follows: HA was positive in 14 cases out of 23 (60.8%), IF in 16/23 (69.5%), standard PCR in 12/20 (60%), and the nested PCR in 1 9/23 (82.6%). Although the correlation among the results of various me thods of virus detection was rather close (r<0.83), the sensitivity of the nested PCR was the highest, both when testing dilutions of PPV an d when analysing the fetal organs. The nested PCR therefore provides a reliable approach for studies of virus distribution in fetal organs, with special reference to potency tests on vaccines.