A New Look at Mumps Encephalitis: Inclusion Bodies and Cytopathic Effects

Abstract

Recent studies by Johnson and Johnson have provided new insights into encephalitis complicating mumps and the pathogenicity of mumps virus for the developing brain. Upon inoculation into suckling hamsters mumps virus induces a destructive ependymitis which, upon healing, leads to an obstructive hydrocephalus. Even neuroadapted strains of the agent, however, have been described as non-neurocytopathic, despite the ability to replicate widely in neurons. Typical cytoplasmic inclusions are induced in tissue culture cells, but inclusions have never been recognized in neural tissues, despite the prominence of specific granular immunofluorescence in ependyma and neurons. We have carried out studies in suckling hamsters using a neuropathic strain of virus and employing fixation and staining methods proven superior for neurovirologic studies to resolve these discrepancies. Widespread cytoplasmic inclusions were observed in neurons, ependyma, and choroid plexus. These inclusions had the same distribution as antigen demonstrated by immunofluorescence and of virus aggregates revealed by electron microscopy, but were fewer and less widespread. Associated cytopathic effects were most prominent in ependyma, but were also present in neurons, particularly in the hippocampus.