Demonstration of vaccinia virus antigen in brains of postvaccinal encephalitis cases.

Five lethal cases of postovaccinal encephalitis (PVE) were examined in attempts to detect the viral antigen by the fluorescent antibody techniques and to isolate the infectious vaccinia virus. Histologically, the brain tissues were characterized by meningoencephalitis, with perivascular infiltrations and inflammatous reactions mainly in leptomininx, chroid plexus and ependyma. By direct immunofluorescence staining, vaccinia virus antigen was found in the brain specimens of one case, but not in the other four cases. The existence of antigen-antibody complexes was suggested by the deposition of immunoglobulins in the brain specimens. After treatment with 3 M NaSCN solution to dissociate the immunoglobulins from the complex, the viral antigen was demonstrated in specimens of two cases. Localization of viral antigen(s) thus detected coincided with that of meningoencephalitic reactions in the histological examination. Virus isolation on chick embryo chorioallantoic membrane was negative in all cases. Participation of viral pathogenicity in the etiology of PVE is discussed.