Bacteria: Borrelia burgdorferi. Spiral shaped spirochaete here colored yellow. Color enhanced scanning electron microscope image Borrelia burgdorferi are 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, principal: Ixodes ricinus in Europe. I. pacificus in North America. Symptoms of lyme disease: skin lesions, muscle pain, neurological and cardiac abnormalities, arthritis. Treatment by antibiotic and corticosteroid drugs. Magnification: x3,000.