Field trial to evaluate the immunogenicity of pseudorabies virus vaccines with deletions for glycoproteins G and E.

OBJECTIVE

To evaluate, under field conditions, the immunogenicity of 2 pseudorabies virus (PRV) vaccines (each with deletion of the gene for glycoprotein G [gG], and 1 with an additional deletion for glycoprotein E [gE]), particularly in the presence of maternal antibodies, and to investigate the effect of vaccination schedules in overcoming maternal antibody interference with vaccination.

SAMPLE POPULATION

Two cohorts of 105 growing pigs each on a PRV-seronegative commercial swine farm where breeding stock had been vaccinated with a PRV vaccine containing deletions of genes for gG and gE.

PROCEDURE

Within each cohort, pigs were randomly assigned to 1 of 7 treatment groups. For each vaccine, vaccination was done at 8, 12, or 8 and 12 weeks of age. One group remained unvaccinated. Blood and nasal swab specimens were obtained at 8, 10, 12, 14, and 16 weeks of age, and the immune response was measured, by use of an ELISA.

RESULTS

In cohort 1, where prevalence of maternal antibodies at 8 weeks of age was lower, an immune response lasting until 16 weeks of age was induced in most pigs by either vaccine. In cohort 2, where prevalence of maternal antibodies at 8 weeks of age was higher, the gG- gE- vaccine elicited a lower immune response in the presence of maternal antibodies than did the gG- vaccine after single vaccination at 8 weeks of age. This maternal antibody interference with the response to vaccination was evident in serum and nasal mucosal antibodies.

CONCLUSIONS

The gE deletion decreases the immunogenicity of PRV vaccine in the presence of maternal antibodies. Although evidence of maternal antibody interference for the gG- vaccine existed, its immunogenicity was diminished less in the presence of maternal antibodies than that of the gG- gE- vaccine.