Background: Tick-borne encephalitis (TBE) is an infectious disease endemic to large parts of Europe and Asia. Diagnosing TBE often relies on the detection of TBEV-specific antibodies in serum and cerebrospinal fluid (CSF) as viral genome is mostly not detectable once neurological symptoms occur. Objectives: We evaluated the performance of TBEV IgM and IgG ELISAs in both serum and CSF of confirmed TBEV patients and discuss the role of (CSF) serology in TBEV diagnostics. Study design: For the assay evaluation we collected specimen from confirmed TBEV patients. Assay specificity was assessed using sera from patients with a related flavivirus infection or other acute infection. A selected ELISA assay was used to analyze TBEV-specific antibodies in CSF and to evaluate the use in confirming TBE diagnosis. Results: In this study the overall sensitivity of the IgM TBEV ELISAs was acceptable (94 -100 %). Four out of five IgM ELISA's demonstrated an excellent overall specificity from 94 -100% whereas a low overall specificity was observed for the IgG TBEV ELISAs (30-71%). Intrathecal antibody production against TBEV was demonstrated in a subset of TBE patients. Conclusions: In four out of five ELISAs, IgM testing in serum and CSF of TBE patients is specific and confirmative. The lack of IgG specificity in all ELISAs emphasizes the need of confirmatory testing by virus neutralisation, depending on the patient's background and the geographic location of exposure to TBEV. A CSF-serum IgG antibody index can support the diagnosis specifically in chronic disease or once IgM has disappeared.

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Keywords Antibody index, Cerebrospinal fluid, Diagnostics, ELISA, Immunoassay, Serology, Tick-borne encephalitis virus, Virus neutralisation
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Journal Journal of Clinical Virology
Reusken, C.B.E.M, Boonstra, M, Rugebregt, S, Scherbeijn, S.M.J, Chandler, F, Avsic-Zupanc, T, … Geurts van Kessel, C.H. (2019). An evaluation of serological methods to diagnose tick-borne encephalitis from serum and cerebrospinal fluid. Journal of Clinical Virology, 120, 78–83. doi:10.1016/j.jcv.2019.09.009