Syphilis (previously called lues) is a sexually transmitted disease (STD) that is caused by a spirochaete bacterium, Treponema pallidum. Syphilis has many alternate names, such as: Miss Siff, the Pox, and has been given many national attributions, e.g. the French disease. 

The route of transmission is almost invariably by sexual contact; however, there are examples of direct contact infections and of congenital syphilis (transmission from mother to child in utero). 

The signs and symptoms of syphilis are myriad; before the advent of serological testing, diagnosis was more difficult and the disease was dubbed the "Great Imitator" because it was so often confused with other diseases. 

In the United States, about 36,000 cases of syphilis are reported each year, and the actual number is presumed to be higher. About three-fifths of the reported cases occur in men. 

If not treated, syphilis can cause serious effects such as damage to the nervous system, heart, or brain. Untreated syphilis can be fatal. If you think you might have syphilis, or if you find out that a sex partner had or might have had syphilis, see a doctor as soon as possible. 

Syphilis can be treated with penicillin or other antibiotics. 

Health care professionals suggest that safer sex practices such as the use of condoms should always be used in sexual activities, but they should by no means be considered an absolute safeguard. The best suggestion is to avoid sexual activities with anyone known to have a sexually transmissible disease, and indeed anyone whose disease-negative status you aren't certain of.