Pseudorabies virus is transmitted among vaccinated conventional pigs, but not among vaccinated SPF pigs

Whereas the reproduction ratio (R) of pseudorabies virus (PRV) in vaccinate d specific pathogen free (SPF) pigs without maternally derived antibodies u nder experimental conditions has repeatedly been shown to be significantly below 1, R in vaccinated conventional pigs in the field with maternally der ived antibodies was significantly above 1. To exclude the difference in hus bandry conditions as a cause for this discrepancy, we quantified and compar ed the transmission of PRV in both groups under identical experimental cond itions. Whereas none of the SPF sentinel pigs became infected (R = 0, signi ficantly < 1), all conventional sentinel pigs did become infected (R = 2.5, significantly > 1). Moreover, only one SPF pigs shed virus in saliva, the mean cumulative titre being almost a 100-fold less than in conventional pig s (17 pigs, P = 0.003). In addition, the mean proliferation of-peripheral b lood lymphocytes in response to PRV antigens was significantly higher in SP F pigs than in conventional pigs at all points studied (P < 0.0001). Moreov er, the virus-neutralising antibody titre after vaccination was significant ly higher in SPF pigs than in conventional pigs. We conclude that the discr epancy in transmission between vaccinated SPF pigs and vaccinated conventio nal pigs cannot be attributed to the experimental conditions. (C) 2001 Else vier Science B.V. All rights reserved.