Lyme disease rash. Close-up of the upper arm of a female patient, showing an erythematous rash around the site of a tick bite. This rash is characteristic of Lyme disease. Lyme disease is an infectious diseased caused by Borrelia sp. bacteria spread through the bite of an infected tick. Early symptoms include fever, headache, fatigue, depression, and a circular skin rash called erythema migrans. Lyme disease patients who are diagnosed early and receive proper antibiotic treatment usually recover rapidly and completely. A key component of early diagnosis is the recognition of the erythema migrans rash that is seen in about 80 percent of Lyme disease patients.