Think of syphilis as the granddaddy of sexually transmitted diseases (STDs). One of the oldest on the books, it's suspected to have affected many over the centuries, including England's King Henry VIII and composer Franz Schubert [source: History]. Syphilis is highly contagious because symptoms are often confused with other problems, if they're apparent at all. Sores can be easily mistaken for mundane annoyances like ingrown hairs, for example, or they hide in the anus or other crevices. If left untreated, syphilis can progress through the uncomfortable first and second stages into the third stage, which is characterized by dementia, heart disease, organ failure and other serious, life-threatening issues [source: Brown University]. No wonder it was referred to in centuries past as the "great pox" or just "the pox."
This disease used to be very widespread. In the early 1900s, it was estimated that 10 to 15 percent of the U.S. population had syphilis [source: Jabbour]. After the introduction of penicillin in the 1940s, the death rate tumbled. Incidence of primary and secondary syphilis in the U.S. in 2013 was down to around 5.3 cases per 100,000 people (but double the all-time low rate reported in 2000 of 2.1) [source: CDC]. Prevention and early treatment of this disease is urged to prevent resurgence and other long-term health complications.