MODEL RELEASED. Erythema migrans rash. This rash, seen here affecting a thigh, is the result of a bite from a tick carrying the bacterium Borrelia burgdorfi. The bacterium infects the skin and causes red patches of rash that can be sore and itchy. Erythema migrans is one of the symptoms of Lyme disease, a common chronic disease in the US and Europe, which causes flu-like symptoms, arthritis, meningitis, and hallucinations. If caught early it can be successfully treated with antibiotics.