Persistence of tick-borne encephalitis virus in monkeys. VI. Pathomorphology of chronic infection in central nervous system.

Histological changes were studied in the central nervous system (CNS) of 58 Macaca rhesus monkeys, infected intracerebrally (i.c.) and subcutaneously (s.c.) with tick-borne encephalitis (TBE) virus. Subacute degenerative process in the CNS occurred in 7 monkeys on days 15-24 post-infection (p.i.), while chronic degenerative changes were observed in 5 monkeys examined on days 45, 90, 279, 383, 789 p.i. Pathological changes in the CNS of 11 monkeys correlated with the clinical picture of subacute and chronic encephalitis. Chronic lesions were observed in the CNS of 1 monkey with asymptotic infection. The pathomorphology of the CNS lesions was characterized by progressive development of focal changes of various duration.