Syphilis is a sexually transmitted bacterial infection caused by the bacterium Treponema Pallidum. Syphilis is passed from person to person through direct contact with syphilis sore. Transmission of the bacterium occurs during vaginal, anal, or oral sex. There are 3 stages of syphilis, all of which are characterized by certain symptoms. Although transmission occurs from persons with sores who are in the primary or secondary stage, many of these sores are unrecognized. Thus, transmission may occur from persons who are unaware of their infection.