When should a test for encephalitis be taken after a tick bite? - briefly
If neurological signs (e.g., headache, fever, confusion) develop, testing is indicated, typically within the 2‑ to 4‑week period after the bite. A baseline serologic sample can also be taken around day 14 even when the patient is asymptomatic.
When should a test for encephalitis be taken after a tick bite? - in detail
Tick‑borne encephalitis (TBE) usually manifests after an incubation period of 7‑14 days, although cases can appear as early as 4 days or as late as 28 days post‑exposure. Testing should be aligned with this window and with the appearance of neurological signs such as headache, fever, neck stiffness, or altered consciousness.
Initial evaluation
- If a patient develops any central nervous system (CNS) symptoms within the first two weeks after a bite, obtain serum and cerebrospinal fluid (CSF) for TBE‑specific IgM and IgG antibodies. IgM appears early in the disease and is the primary diagnostic marker.
- In the absence of neurologic signs, routine testing is not recommended; observation for fever or flu‑like illness is sufficient.
Laboratory timing
- Day 0‑3 post‑symptom onset: PCR for TBE virus RNA may be positive in blood or CSF, but sensitivity is low. A negative result does not exclude infection.
- Day 4‑10 post‑symptom onset: IgM antibodies become reliably detectable in serum; CSF IgM is also often present. This is the optimal period for serologic confirmation.
- After day 10: IgG titers rise and can be used to confirm recent infection, especially if IgM persists. Paired serum samples taken 2‑3 weeks apart improve diagnostic certainty.
Follow‑up testing
- If the first serologic assay is negative but clinical suspicion remains high, repeat testing after 7‑10 days. A seroconversion (appearance of IgM or a four‑fold rise in IgG) confirms the diagnosis.
- For patients with delayed neurologic involvement (> 14 days), testing should be performed as soon as symptoms appear, regardless of the initial bite date.
Guideline summary