Syphilis is a sexually transmitted infection (STI) caused by the bacterium Treponema pallidum. The most common initial symptom is a painless sore called a chancre (say "shanker") that develops on the genitals.
Syphilis can be easily cured with antibiotics. If syphilis is not treated, it can eventually lead to serious health problems, such as blindness or heart problems.
WebMD Medical Reference from Healthwise