Treponema pallidum. Computer graphic depicting a group of Treponema pallidum bacteria. These spirochaete bacteria are spirally-twisted forms, elongated and appearing thread-like. They cause syphilis in humans. Treponema pallidum is sexually transmitted, and may also be passed from an infected pregnant woman to her unborn child (congenital syphilis). The disease has 3 stages: the last stage (tertiary syphilis) may cause severe damage to the heart, blood vessels, brain and spinal cord. Treatment with penicillin drugs is effective if administered in the early stages. Magnification: x2000 at 6x4.5cm size.