Syphilis - a sexually transmitted infection (STI), once responsible for devastating epidemics. The initial infection causes an ulcer at the site of infection. The bacteria, however, move throughout the body, damaging many organs over time. Medical experts describe the course of the disease by dividing it into four stages-primary, secondary, latent, and tertiary (late). An infected person who has not been treated may infect others during the first two stages, which usually last 1 to 2 years. In its late stages, untreated syphilis, although not contagious, can cause serious heart abnormalities, mental disorders, blindness, other neurologic problems, and death. In addition, a pregnant woman with syphilis can pass T. pallidum to her unborn child, who may be born with serious mental and physical problems as a result of this infection.