Latent herpes simplex virus trigeminal ganglionic infection in mice and demyelination in the central nervous system

Mice were inoculated with herpes simplex virus (HSV) type 1 by gently scraping the skin of the nose with a fine needle. About 80% of the animals developed latent inapparent HSV infections in trigeminal ganglia. Virus was demonstrable for at least 6 months post inoculation (p.i.) by cocultivation of ganglionic tissue with GMK cells. Histologically, trigeminal ganglia revealed infiltrations of inflammatory cells even 6 months p.i. In addition, lesions occurred in the brainstem corresponding to the entry of trigeminal roots, trigeminal tracts and nuclei. Inflammatory cell infiltration, disruption of myelin sheaths and macrophages laden with myelin degradation products were observed 7 days p.i. Fourteen to 30 days p.i. electron microscopy demonstrated completely naked axons. In the transitional region of the trigeminal root denuded axons occurred in the central part of the region while the peripheral myelin, bordering the demyelinated central segments, was intact. Small areas of demyelination were still detectable 3 and 6 months p.i. but there were then also signs of remyelination. Possible mechanisms causing the demyelinations are discussed.