Syphilis is a STI caused by the Treponema Pallidum bacteria. It is highly infectious and easily spreadable, and treating it once does not mean you will not catch it again.
It is possible to be infected without having symptoms, however symptoms can include:
Testing for Syphilis usually involves a blood test and removing a sample of fluid from any sores using a swab. Treatment comes in the form of antibiotic injections and tablets. Furthermore, you should avoid any kind of sexual contact with another person until at least two weeks after your treatment finishes.