Non-pathogenic strains of Aujeszky's disease virus are not reactivated in swine after corticosteroid treatment.

1. The Bartha-K and NIA-4 strains of Aujeszky's disease virus (ADV) were readily isolated from oropharyngeal swabs up to 7 days after intranasal vaccination of young piglets. 2. Neither strain could be reisolated 14 days after starting treatment with 10 mg of the corticosteroid isoflupredone acetate per kg of body weight, administered intramuscularly for 4 consecutive days when pigs were 7-9 months of age. 3. Similar treatment with corticosteroid pigs infected with two virulent ADV strains resulted in the reactivation of infection and recovery of ADV from oropharyngeal swabs. 4. Serum neutralizing antibodies were present in all piglets vaccinated twice (2 week interval) intranasally with the attenuated ADV strains, 4 weeks after primary vaccination. However, these antibodies were no longer detectable in some pigs at 12 (NIA-4) and 20 (Bartha-K) weeks of age even in undiluted sera. 5. Neutralizing antibodies resulting from infection with virulent ADV were always detectable, were higher in titer than those produced by the vaccine strains and did not vary in a clear pattern after corticosteroid treatment. 6. These results indicate that the Bartha-K and NIA-4 strains undergo little or no latency in swine and confirm the latency of virulent strains of ADV.