Syphilis is a complex sexually transmitted infection (STI) caused by the bacteria
Treponema pallidum. Episodes of active disease occur, followed by latent periods, when the
person remains infected but there are no signs or symptoms.
Initially syphilis appears as a painless sore (ulcer) where the infection entered (usually
around the genitals) and may go unnoticed. The sore is known as a chancre and this phase
is known as primary syphilis.
Widespread rash and 'flu-like symptoms appear next (secondary syphilis).
If left untreated, tertiary syphilis may develop years later and cause a variety of
problems affecting the heart, eyes, brain & bones.