Syphilis is almost always transmitted through sexual contact with an infected person, who is almost always displaying the sores on the genitals typical of the disease. The use of condoms is usually effective in preventing the transmission of the disease between partners. In females, the sores are often inside the vagina and therefore more difficult to detect. In males, the sores most often appear on the penis.
The sores will spontaneously heal in a few weeks, but the bacteria will continue to grow within the body, forming granulomas which protect the bacteria from the body's immune system. In addition, syphilis can go through long periods of latency between outbreaks where, although the disease can be treated and tested for, it is not contagious and shows no symptoms.
Prior to the beginning of the 20th century, there was no effective treatment for the disease. In the 20th century, the development of arsenic-based drugs did allow the disease to be treated if it were caught before it caused nerve damage. However, such drugs were not effective against late stage syphilis. However, penicillin turned out to be an effective treatment for the disease even in its late stages, and remains the preferred treatment to this day, with almost all strains of the disease being susceptible to this antibiotic.
Patients with syphilis are usually required to tell the treating physician the names of their sexual contacts so that they can be advised by health departments to get treated for the disease.