Neuropathology of S. Paulo south coast epidemic encephalitis (Rocio flavivurus).

The neuropathology of 8 cases of S. Paulo south coast epidemic encephalitis (Rocio flavivirus), a new arbo B virus encephalitis, is described. The topographic pattern of the lesions appears to be almost specific. The gray matter is predominantly affected. Interstitial mononuclear infiltration, microglial proliferation and perivascular lymphocytic cuffing were seen. Neuronophagia was seldom seen except during the acute phases of the disease. Throughout the neuraxis, the gray matter was affected to a greater degree than white matter. The more damaged structures, in descending order, were as follows: thalamus, dentate nucleus, substantia inominata, brain stem, spinal cord and basal nuclei. Most of the cases exhibited thalamic inflammatory necrosis. Electron microscopy disclosed in one case virus-like particles, resembling those described in other arbo B viruses in the cytoplasm of thalamic neurons. In this case, virus was isolated from the brain and an immunofluorescence test also showed antigenic material in the thalamic neurons.