Herpes simplex encephalitis. An immunohistological study of the distribution of viral antigen within the brain.

An immunoperoxidase technique was used to map the sites of herpes simplex virus antigen (VA) within the brain in 29 autopsied cases of herpes simplex encephalitis. Attention was directed particularly to those parts of the brain that are known from pathological studies to be involved in the disease. Material was studied from cases surviving for varying periods from a few days to a few years after the onset of neurological disease. VA was found within the brain in all cases dying within 3 weeks of onset, but in none dying thereafter. VA was already most abundant in patients dying within the first week and remained plentiful during the first 16 days. Inflammation and necrosis reached a peak when detectable virus was waning. VA was concentrated mainly in the medial and inferior temporal lobes, hippocampus, amygdaloid nuclei, olfactory cortex, insula and cingulate gyrus. It was invariably present on both sides of the brain but was more abundant on one side than the other. Virus was found in glial cells of the olfactory tracts but not in relation to trigeminal pathways. Attention is drawn to focally extensive infection of the granule cell of the dentate fascia, and the possible significance of this finding is discussed.