Color enhanced scanning electron microscope image of the bacteria Borrelia burgdorferi, the cause of Lyme-disease in humans. Spiral shaped spirochaete here colored yellow. The bacterium occurs in the midgut of ticks and is transmitted to humans by tick bites. Several tick species harbor these bacteria, principal: Ixodes scaplularis in North America and Ixodes ricinus in Europe. Symptoms of lyme disease: skin lesions, muscle pain, neurological and cardiac abnormalities, arthritis. Treatment is by antibiotics and corticosteroid drugs.