Primary syphilis is manifested after an incubation period of 10-90 days (average 21 days) after exposure with a primary sore. The sore, called a chancre, is localized at the point of initial exposure to the bacterium, often on the penis, vagina or rectum. Depression-era U.S. poster advocating early syphilis treatment Syphilis (historically called lues) is a sexually transmitted disease (STD) that is caused by a spirochaete bacterium, Treponema pallidum. ... The penis (plural penises or penes) is in addition to the scrotum one of the external male sexual organs. ... Human female internal reproductive anatomy. ... The posterior aspect of the rectum exposed by removing the lower part of the sacrum and the coccyx. ...