Serological Evidence of Tick-Borne Encephalitis Virus (TBEV) Exposure Among Hospitalized Neurological Patients in Israel, 2010–2019

Background: Tick-borne encephalitis virus (TBEV) is an important cause of neuroinvasive infection in Europe and Asia. Israel is considered nonendemic, yet travel-associated cases have been reported. Methods: Sera from hospitalized neurological patients in Israel (2010–2019) were screened for TBEV IgG antibodies. Positive/borderline results were confirmed by virus neutralization testing (VNT) against both TBEV and West Nile Virus (WNV). Confirmed TBEV-neutralizing sera were tested for anti-TBEV IgG and IgM by immunofluorescence assay. Results: Of 12,651 suspected meningitis/encephalitis cases, 1,280 (10.1%) were screened. Sixty-three were ELISA-IgG positive/borderline (4.9%), and VNT confirmed TBEV neutralization in 9 (0.7% of the 1,280 patients). West Nile Virus (WNV) Virus neutralization test (VNT) was positive in 51/63 samples. Two samples neutralized both viruses. All TBEV VNT-positive sera were IgM-negative. Conclusions: Confirmed TBEV exposure was rare with no evidence of missed acute TBE infection. Most apparent TBEV ELISA reactivity reflected WNV cross-reactivity. Parallel VNT against WNV and TBEV is essential in WNV-endemic countries for accurate TBEV diagnosis.