Pathologic changes in pigs with prednisolone-induced recrudescence of herpesvirus infection

In pigs inoculated with Aujeszky's disease virus (ADV), recrudescence of herpesvirus infection was induced by daily administration of 1,000 mg of prednisolone for 5 days at 2 (group A) or 5 (group B) months after the primary infection. At necropsy in group A pigs, ADV was recovered from nasal secretions 3 to 9 days after prednisolone treatment initiation and from the brain cortex 10 days after treatment initiation; ADV was not recovered from group B pigs. In pigs of both groups killed 10 days after treatment initiation, 2 types of characteristic lesions were found. One type was a nonsuppurative encephalitis that consisted of neuronal necrosis, neuronophagia, and formation of eosinophilic intranuclear inclusion bodies. The 2nd type had basophilic intranuclear inclusion bodies in the enlarged endothelial cells of the kidneys, liver, lungs, adrenal glands, and lymph node sinusoids. Cells containing intranuclear inclusion bodies had immature and mature herpesvirus particles. Therefore, the brain lesions containing the eosinophilic inclusion bodies were considered to be due to ADV. Basophilic inclusion bodies in the endothelial cells were due to porcine cytomegalovirus. These observations indicated that prednisolone treatment resulted in recrudescence of ADV and porcine cytomegalovirus infections.