Syphilis is caused by Treponema pallidum , a spiral-shaped bacterium called a spirochete. Syphilis is spread from person to person. A person gets syphilis from direct contact with a syphilis sore on the body of an infected person. Sores occur at the site of infection, mainly on the external genitals, vagina, anus, or rectum. Sores can also be on the lips and in the mouth.
Transmission occurs during vaginal, anal, or oral sex.
An infected pregnant woman can also pass the disease to her unborn child. Syphilis cannot be spread by contact with toilet seats, door knobs, swimming pools, hot tubs, bathtubs, shared clothing, or eating utensils. The chancre is usually firm, round, small, and painless. It appears at the spot where the bacteria entered the body. Chancres last 1 to 5 weeks and heal on their own.