Comparison of in vivo reactivation, in vitro reactivation, and polymerase chain reaction for detection of latent pseudorabies virus infection in swine.

The following methods were compared for their ability to detect latent pseudorabies virus in 24 pigs that had been experimentally infected with virulent pseudorabies virus: 1) in vivo reactivation by dexamethasone administration, 2) in vitro reactivation by 5 different techniques of explant culture or cocultivation of trigeminal ganglia, and 3) detection of pseudorabies virus genome in tissue digests of tonsils or trigeminal ganglia using the polymerase chain reaction. Reactivation of pseudorabies virus by administration of dexamethasone was attempted in 12 of 24 pigs in an effort to determine if this procedure would affect the detection of latent pseudorabies virus by any of the subsequent in vitro methods. Detection of latent virus by the polymerase chain reaction with trigeminal ganglia was the most successful method (24/24 were positive). The next most successful method was in vivo reactivation through the administration of dexamethasone (10/12 [83%] were positive). Only 1 in vitro reactivation technique, cocultivation involving digestion of the trigeminal ganglia with trypsin and collagenase and the addition of a hypomethylating agent to the medium, yielded positive results (5/24 [21%] were positive). The polymerase chain reaction performed on tissue digests of tonsils was much less effective (2/24 [8%] were positive) than it was with trigeminal ganglia. Reactivation by dexamethasone did not appear to have any effect on the subsequent detection of latency by any of the methods tested.