Human eastern equine encephalitis: immunohistochemistry and ultrastructure.

The brain of a 7-year-old boy who died of eastern equine encephalitis (EEE) was examined by immunohistochemical and ultrastructural techniques to detect the presence and distribution of viral antigen. A mouse polyclonal antibody was most effective for demonstrating the presence of antigen previously unreported in this disease in humans. Antigen was localized to the perikaryon and dendrites of neurons; little was detected in glial cells. Cell death by apoptosis was conspicuous, but it was primarily identified in glial and inflammatory cells. Neuronal death was most commonly marked by cytoplasmic swelling or eosinophilia and nuclear pyknosis. A disassociation between the degree of inflammation and the presence of antigen was noted, especially in cerebral cortex and spinal cord, presumably where infected cells already had been cleared. Ultrastructurally, rare mature viral particles were seen in extracellular spaces.