Syphilis is caused by the bacterium Treponema pallidum. It is typically transmitted through sexual contact, including vaginal, anal, and oral sex. However, it is important to note that syphilis can also be transmitted from an infected mother to her unborn child during pregnancy or childbirth. This is known as congenital syphilis. It is essential to practice safe sex and undergo regular testing to prevent the transmission of syphilis and protect one's sexual health.