Development of active immunity in newborn pigs with colostral antibodies by vaccination with gIII-deleted PRV

Maternal antibodies interfere with active immunization of swine by gI-deleted pseudorabies virus [(PRV); Aujeszky's disease virus] vaccines. To test the hypothesis that modified-live (MLV) vaccines retaining the PRV gI and with deletions in the PRV glycoprotein gIII and thymidine kinase (TK) genes might be efficacious in circumventing colostral antibody interference, the OMNI-MARK-PRV (gI+ gIII- TK-) vaccine was administered intramuscularly to 13 newborn pigs with colostral antibodies, while 10 pigs from the same litters served as nonvaccinated controls. At 49 days of age, when PRV virus neutralization (VN) antibodies were negative and all nonvaccinated pigs as well as 10 vaccinates were latex agglutination test (LAT)-negative, the pigs were challenged intranasally with the virulent PRV(SHOPE) strain. In support of the hypothesis, it was found that several central nervous system and respiratory disease signs developed in 6 of 10 nonvaccinates, with one fatality, while 2 of 13 vaccinates showed only very mild and transient disease signs. Nonvaccinates lost weight until post challenge day (PCD) 6, did not regain prechallenge weight until PCD 8, and at PCD 11 had gained only 4.9 pounds/pig. Vaccinates gained weight after challenge and at PCD 11 showed a 9.4 pounds/pig weight gain. On PCD 11, the geometric mean titer (GMT) for VN antibodies of the nonvaccinates was 9.3, while the GMT of the vaccinates for VN antibodies was 49.0, showing that vaccinated pigs had been immunologically primed.