How to know if a tick is infected with Borrelia? - briefly
The only reliable method is laboratory testing of the tick (e.g., PCR or culture) after removal; external appearance or size does not indicate infection. If testing is unavailable, monitoring the bite site for erythema migrans and seeking medical evaluation is advised.
How to know if a tick is infected with Borrelia? - in detail
Identifying a tick that carries the bacterium responsible for Lyme disease requires a combination of visual assessment, laboratory analysis, and timing considerations.
A tick removed within 24 hours of attachment is unlikely to have transmitted the pathogen, because Borrelia burgdorferi migrates from the midgut to the salivary glands after approximately 36–48 hours of feeding. Therefore, the duration of attachment provides an initial risk estimate.
Visual cues are not reliable for infection status. Engorgement level, species, and life stage (larva, nymph, adult) influence probability, but no external characteristic definitively indicates bacterial presence.
Definitive determination relies on testing the specimen:
- Polymerase chain reaction (PCR) – amplifies Borrelia DNA from tick tissue; highly sensitive, especially for nymphs and adults.
- Culture – isolates live spirochetes on specialized media; low sensitivity, time‑consuming, reserved for research labs.
- Immunofluorescence assay (IFA) – detects Borrelia antigens in tick sections; useful for confirming PCR results.
- Enzyme‑linked immunosorbent assay (ELISA) – measures antibodies against Borrelia in the tick; less common, may yield false positives.
Testing protocols differ by region; many public health laboratories accept ticks submitted by the public, often requiring a fee and proper preservation (e.g., in 70 % ethanol or frozen at –20 °C).
If a tick is identified as infected, the following actions are recommended:
- Initiate prophylactic antibiotic therapy within 72 hours of removal for high‑risk exposures, following local guidelines.
- Monitor the bite site for erythema migrans or systemic symptoms (fever, headache, fatigue) for up to 30 days.
- Document species, life stage, attachment time, and test results for medical records.
In summary, visual inspection cannot confirm infection. Accurate assessment depends on laboratory testing of the removed arthropod, combined with knowledge of attachment duration and tick biology. Prompt testing and appropriate clinical response reduce the likelihood of Lyme disease development.