Morgardt et al.
Kinetics of tick-borne encephalitis virus IgM antibody responses in serum and cerebrospinal fluid. Infect Dis (Lond). 2025;57(7):676-686. doi:10.1080/23744235.2025.2473496
Tick-borne encephalitis (TBE) virus infection is primarily diagnosed through serological testing, detecting specific IgM and IgG antibodies. A weak or delayed intrathecal IgM response has been associated with more severe disease during the acute phase. This study aimed to investigate the kinetics of TBE virus-specific IgM antibody levels in both serum and cerebrospinal fluid (CSF) during disease onset and follow-up, and to explore potential correlations between antibody levels, disease severity, and residual symptoms.
The study demonstrated a significant increase in IgM levels during the first 4–5 weeks following symptom onset, in both serum and CSF. Peak IgM concentrations were observed in serum between days 22 and 30, and in CSF between days 31 and 45 after the onset of fever. In individual cases, IgM antibodies remained detectable in both compartments for up to one year post-infection. This prolonged detectability suggests an extended diagnostic window for lumbar puncture beyond the acute phase, potentially increasing the number of confirmed TBE cases.
For the majority of patients, IgM levels were higher in CSF than in serum at the final sampling point, suggesting that IgM may persist longer in CSF. IgM positivity was frequently observed in both serum and CSF as early as the first week in cases of monophasic disease. Notably, better clinical recovery at three months was associated with higher IgM levels in both serum and CSF; however, this association remained statistically significant only for CSF at the six-month follow-up. Additionally, two out of three previously vaccinated patients exhibited an early IgM response within the first week of illness.