Virus-Induced Demyelination

Viral infection of the nervous system is usually accompanied by a predominantly mononuclear cell inflammatory response. Factors to be considered in discussing viral demyelination include exposure to the virus, ability of the virus to invade and infect the nervous system, the types of nervous system cells infected, the role of the immune response in viral clearance, and the pathogenic mechanism of any immune-mediated damage and the target antigens. Viruses associated with demyelination have no apparent common features; they include viruses from several different taxonomic groups, DNA and RNA viruses and enveloped and nonenveloped viruses. The key cell in CNS demyelination is clearly the oligodendrocyte. Each oligodendrocyte may myelinate many internodes; hence, destruction of one oligodendrocyte has a greater morphological impact than destruction of one neuron or one Schwann cell as regards lesions of demyelination. Multiple sclerosis is the most common demyelinating human disease and has often been suggested to have a viral etiology.