The most common VECTOR carried disease in Europe and North America; it is caused by a SPIROCHAETE, Borrelia burgdorferi, which is transmitted by tick bite. Every year in England & Wales 2–3 thousand cases are reported. Typically it comprises fever, ’flu-like symptoms and a particular skin rash, erythema migrans; this is a lesion that looks like the bulls-eye on a dart board, with a central dense pink area, surrounded by an outer pink rim. Several may occur over days. Early diagnosis is by the clinical appearance and blood testing and treatment with antibiotics generally leads to recovery. However, some patients develop problems many months or even years later, including ARTHRITIS, neurological symptoms of various sorts and evidence of cardiac muscle disease. Others experience a persistent condition akin to CHRONIC FATIGUE SYNDROME (CFS) but uncertainty remains about the precise relationship of this with the original infection.