Tick-Borne Encephalitis: A Differential Pattern of Intrathecal Humoral Immune Response and Inflammatory Cell Composition Compared with Other Viral CNS Infections

To investigate whether and how cerebrospinal fluid (CSF) findings can contribute to distinguish tick-borne encephalitis (TBE) from herpes simplex virus (HSV) and varicella zoster virus (VZV) induced central nervous system (CNS) infections (HSV-I, VZV-I). Chart review and identification of TBE, HSV- I, and VZV-I was carried out, fulfilling the following criteria: (1) clinical signs of encephalitis and/or meningitis, (2) complete CSF analysis and confirmed viral etiology by either PCR or antibody testing in CSF, (3) hospitalized patients, and (4) available brain magnetic resonance imaging (MRI). Fifty-nine patients with 118 CSF/serum pairs were included. These comprised 21 with TBE (35 CSF/serum pairs), 20 (40 CSF/serum pairs) with HSV-I, and 18 (43 CSF/serum pairs) with VZV-I. In contrast to HSV-I and VZV-I, CSF cell differentiation in TBE showed more often an increased (>20%) proportion of granulocytes (p < 0.01) and a more frequent quantitative intrathecal IgM synthesis (p = 0.001 and p < 0.01, respectively), while the second was even more pronounced when follow-up CSF analyses were included (p < 0.001). CSF findings help to distinguish TBE from other viral infections. In cases with CSF pleocytosis and a positive history for a stay in or near an endemic area, TBE antibodies in CSF and serum should be determined, especially if granulocytes in CSF cell differentiation and/or an intrathecal IgM synthesis is present.