Caused by a bacterium called Treponema pallidum. This family of bacteria can also cause tropical diseases called Yaws and Pinta. Syphilis is usually a sexually transmitted infection which, if untreated, can cause serious disease. Yaws and Pinta cause skin and joint problems. All three diseases are fully treatable with antibiotics. The tests we use look for specific antibodies to the bacterium. These antibodies remain in a person’s blood many years after the infection has gone. A positive test for syphilis often relates to an infection in the past, but we are not able to use blood as long as the test is positive.