Tick-borne encephalitis--pathogenesis, clinical course and long-term follow-up.

The prospective studies available today confirm the experience gained from several retrospective studies that TBE is a disease with a severe acute clinical course and considerable long-term morbidity. A defined post-encephalitic TBE syndrome exists, causing long-lasting morbidity that often affects the quality of life and sometimes also forces the individual to a change in life-style. The sequelae render high costs for individual patients and the society. Three clinical courses may be identified: one with complete recovery within 2 months, occurring in approximately one fourth of patients, one with protracted, mainly cognitive dysfunction, and one with persisting spinal nerve paralysis with or without other post-encephalitic symptoms. Up to 46% of patients are left with permanent sequelae at long-time follow-up, the most commonly reported residuals being various cognitive or neuropsychiatric complaints, balance disorders, headache, dysphasia, hearing defects, and spinal paralysis. This knowledge enhances the need for continued local epidemiological surveillance of TBE to form a basis for vaccination policies. Even though knowledge of the clinical course of TBE has improved in recent years, there are still several aspects of this disease that warrant further studies. These comprise the clinical picture and prognosis in children, an evaluation of different rehabilitation strategies, and an improved understanding of pathogenic mechanisms to permit the development of antiviral or, maybe more probable, immune modulatory treatment strategies. Copyright 2002 Elsevier Science Ltd.