Erythema migrans
Type: Symptom
Definition
An expanding, distinct skin rash that frequently resembles a target or bullseye.
Clinical Details
As the highly motile spirochetes migrate outward from the initial tick bite through the dermal tissues, they trigger a localized, expanding wave of inflammation. This creates a large, circular red rash with a clear central clearing, visually mimicking an archery target. It is the pathognomonic early sign of the infection, though it does not appear in all patients.