English: This 2009 photograph depicts the pathognomonic erythematous rash in the pattern of a “bull’s-eye”, which manifested at the site of a tick bite on this french leg of young booy who’d subsequently contracted Lyme disease.

Lyme disease patients who are diagnosed early, and receive proper antibiotic treatment, usually recover rapidly and completely. A key component of early diagnosis is recognition of the characteristic Lyme disease rash called erythema migrans. This rash often manifests itself in a “bull's-eye” appearance, and is observed in about 80% of Lyme disease patients.

Lyme disease is caused by the bacterium Borrelia (B. Burgdorferi in usa, or some other species of borrelia in the world), and is transmitted to humans by the bite of infected blacklegged ticks. Typical symptoms include fever, headache, fatigue, and as illustrated here, the characteristic skin rash called erythema migrans. If left untreated, infection can spread to joints, the heart, and the nervous system. Note that there are a number of PHIL images related to this disease and its vectors.