Pacheco's disease in psittacine birds.

Pacheco's disease, caused by a herpesvirus, was diagnosed in 20 groups of 47 psittacine birds received for necropsy. A tentative diagnosis, based on history and gross lesions, was confirmed by one or more of the following observations: Cowdry type A inclusions in the hepatocytes and cells of other affected tissues, pathogenicity of tissue suspensions for chicken embryos, cytopathic effects of herpesvirus in monolayers of chicken embryo fibroblasts, and demonstration of herpesvirus in cell-culture fluid by electron microscopy.