Syphilis is caused by the bacterium Treponema Pallidum. This STD is known as the ‘great imitator' because it can cause many different signs and symptoms, making it difficult to distinguish syphilis from other medical conditions. Syphilis is spread through direct contact with someone who has a syphilic sore (chancre). The sore may appear anywhere on the genitals (internal or external), in the mouth, rectum or where there was close intimate contact (including hands, inner thighs, etc.). If diagnosed early, syphilis is easily treated with antibiotics.

The following sources provide excellent information about this infection:

Centers for Disease Control 

Centers for Disease Control Fact sheet for MSM

New York State Department of Health

Women's Health.gov

Planned Parenthood

The Mayo Clinic

National Library of Medicine