Color enhanced scanning electron micrograph of Borrelia burgdorferi, the cause of lyme-desease in humans. They are passed on to humans by tick bites and occur in the midgut of the tick. Several tick species harbor these bacteria, principally: Ixodes ricinus in Europe and I. pacificus in North America. Symptoms of lyme disease: skin lesions, muscle pain, neurological and cardiac abnormalities, arthritis. Treatment by antibiotic and corticosteroid drugs.