Efficacy of an intranasal immunization with gEgC and gEgI double-deletion mutants of Aujeszky's disease virus in maternally immune pigs and the effects of a successive intramuscular booster with commercial vaccines.

In this study, an intranasal immunization strategy was set up in maternally immune pigs in order to protect them not only clinically but also virologically. Two genetically engineered Aujeszky's disease virus (ADV) strains, Kaplan gE-gI- and Kaplan gE-gC-, were used for intranasal immunization. Both strains were safe for 4-week-old pigs. A single intranasal inoculation of 10(6.0) TCID50 of Kaplan gE-gI- and Kaplan gE-gC- at 4 weeks of age in the presence of moderate titres of maternally derived antibodies (SN titres: 12-16) reduced the amount of weight loss, fever and virus excretion upon challenge 6 weeks later. In a second experiment, the effect of an additional intramuscular booster with three different commercial vaccines (containing attenuated Bartha or NIA3-783 or inactivated Phylaxia; all suspended in an oil-in-water emulsion) at 10 weeks of age was evaluated. One month after the last intramuscular booster, between five and seven pigs from each group were selected for challenge. All intranasally/intramuscularly immunized pigs showed a significantly better clinical and virological protection after challenge than the single intranasally immunized pigs. In the double immunized group, the protection was better when Kaplan gE-gC- was used for the intranasal priming (only two of 14 pigs excreted virus with a duration of 4 days) than when Kaplan gE-gI- was used (13 of 18 pigs excreted virus with a duration ranging from 1 to 4 days). The virological protection was not influenced by the type of vaccine used for booster vaccination. Because the intranasal/intramuscular immunization approach is very compatible with current pig movements on farms and pigs with moderate levels of maternally derived antibodies can effectively be immunized, it can be considered as a good alternative to intramuscular/intramuscular vaccinations especially in regions with a high ADV prevalence.