[Ultrastructural changes in the CNS of monkeys with the chronic form of tick-borne encephalitis].

The central nervous system of monkeys with chronic tick-borne encephalitis (TBE) shows the following ultrastructural alterations which differ from those in acute TBE: widespread destructive changes in neurons, astrocytes, oligodendrocytes, processes, myelin, vascular walls, severe edema of brain tissue with the signs of a so-called spongious degeneration and the absence of cell proliferation and perivascular cell infiltrations, glial nodules as well as circulatory disorders (hyperemia, stasis, hemorrhages). Few virions with or without and altered supercapsid membrane are detected in the neuronal cytoplasm or in the intercellular spaces; the signs of active virus reproduction in the cells are lacking. Pathologic process is of a degenerative but not of an inflammatory nature; the latter is typical for acute TBE.