"Erythema migrans is the only manifestation of Lyme disease in the United States that is sufficiently distinctive to allow clinical diagnosis in the absence of laboratory confirmation." Often, but not always, mentions of a
target lesion (bull's-eye lesion) are talking about erythema migrans. However, the appearance of erythema migrans can vary considerably: while some look like a bull's eye, in the U.S. most are evenly red or bluish, without a central or ring-like clearing. A minority of patients never have any rash. Because Lyme disease can within a few weeks cause long-term neurologic complications, persons with a rash and recent history of outdoor activities where Lyme is common should seek a doctor for diagnosis. The EM rash is often accompanied by symptoms of a viral-like illness, including fatigue, headache, body aches, fever, and chills, but usually not nausea or upper-respiratory problems. These symptoms may also appear without a rash, or linger after the rash disappears. Lyme can progress to later stages without these symptoms or a rash. A person with an asymptomatic EM rash can easily miss its significance. However, if the initial EM rash is not treated, the infection can disseminate through the lymphatic system or blood. Within days or weeks, additional EM rashes, usually smaller, can appear at other sites, or the infection can cause more serious complications in the nervous system, heart, or joints. ==Southern tick-associated rash illness==