Syphilitic man. Artwork of a syphilitic man shooing prostitutes from his bedroom. Syphilis is a sexually transmitted infection caused by the bacteria Treponema pallidum. The disease has three stages, first an ulcer at the site of infection followed several weeks later by a systemic skin rash. The third stage, which follows a latency period that can last for years, involves spread to the organs and nervous system and can cause mental illness and death. Caricature from France, circa 1800-1810.