Circumvention of maternal antibody interference by immunization of newborn pigs with glycoprotein gIII-deleted marker vaccine.

Maternal antibodies interfere with the immunization of swine by modified live-virus pseudorabies virus (PRV) vaccines. To test the hypothesis that a PRV vaccine attenuated by deletions in the thymidine kinase (TK) and gIII genes might reduce interference by maternal antibodies, pigs with moderate to low levels of colostral PRV antibodies were immunized with the TK- gIII-OMNIMARK-PRV vaccine. Vaccinates and non-vaccinates were challenged intranasally with virulent PRV at 7 weeks of age. In support of the hypothesis, it was found that central nervous system (CNS) and/or respiratory disease developed in six out of 10 controls with a fatal outcome in one, while two out of 13 vaccinates showed only very mild and transient CNS or respiratory disease signs with no fatalities. All vaccinates gained weight while non-vaccinates initally lost weight. At post-challenge day (PCD) 11, vaccinates showed 4.5 lb/pig greater weight gain than non-vaccinates. Virus neutralization (VN) analyses before and after challenge showed that vaccinates had been primed immunologically. In another experiment, newborn pigs from a pseudorabies disease-quarantined herd with high VN antibody titres were vaccinated, respectively, with the gIII-TK-OMNIMARK-PRV vaccine, a TK-gI-gX-vaccine, or no vaccine and challenged with virulent PRV at 14 weeks of age when VN titres were < 1:2. By PCD 9, the TK-gIII-group had outgained the TK-gI-gX- and the control groups, respectively, by 6.0 and 3.2 lb per pig.