AIDS is a sexually transmitted disease caused by infection with the human immunodeficiency virus and is transmitted mainly through sexual contact, blood transmission and mother-to-child transmission. A disease with similar transmission routes as AIDS is syphilis. Syphilis is a sexually transmitted disease caused by infection with the syphilis spirochete. It is transmitted mainly through sexual contact, blood transmission, and mother-to-child transmission. When a person with syphilis has sex, the skin mucous membrane is broken and the syphilis spirochete enters the body, which multiplies and causes syphilis. It is possible to contract syphilis by entering blood contaminated with syphilis spirochetes or by being pricked with a needle infected with syphilis spirochetes. A mother with syphilis can transmit it to her fetus through the placenta.