Kinetics of tick-borne encephalitis virus IgM antibody responses in serum and cerebrospinal fluid.

Background: Tick-borne encephalitis (TBE) is a viral disease primarily spread by ticks. The diagnosis is mainly based on detection of IgM and IgG antibodies against TBE virus (TBEV) in serum and cerebrospinal fluid (CSF). The kinetics of TBEV IgM in the CSF is largely unexplored.

Objectives: Our aim was to determine the duration and strength of the IgM antibody response in serum and CSF during and after previously diagnosed clinical TBE, and to investigate whether such antibody levels correlated with severity and residual symptoms.

Methods: Sixty-nine paired samples from serum and CSF of 31 TBE patients were analysed with the ReaScan TBE IgM test both in the emergency stage and during repeated follow-up visits for up to six years. Recovery was evaluated with Glasgow outcome scale (GOS), a global scale for assessing disability and social participation.

Results: At the first sampling, 30/31 patients were TBEV IgM positive in serum and 28/31 in CSF. In individual patients, IgM antibodies were detected in both body fluids up to one year after onset of disease. No association was found between IgM levels and disease severity. However, patients with better recovery at 3 months' follow-up had significantly higher levels of IgM in serum and CSF compared to patients with severe disability.

Conclusions: Detection of TBEV IgM antibodies facilitates early diagnosis and in cases where the IgM response is long-lasting, there is an opportunity for diagnosis later after onset of disease. Improved recovery after three months seems to be associated with stronger IgM response.