A contagious, sexually-transmitted disease caused by the bacteria, Treponema pallidum. The disorder occurs in three stages with each stage more severe. The first stage, primary syphilis, causes a painless sore that is usually in the genital area. The second stage ("secondary syphilis") causes fever, rash, and joint pain. Advanced syphilis ("tertiary syphilis") causes brain or heart or blood vessel injury and can result in irreversible damage.