Syphilis is a sexually transmitted disease caused by

The correct option is A Treponema pallidum
Syphilis is one type of sexually transmitted disease. Syphilis is the result of a bacterial infection of the genital tract by the bacterium, Treponema pallidum. Syphilis is passed from one person to another during direct sexual contact with a syphilis lesion that involves vaginal, oral, or anal sex. Syphilis can also be passed from an infected mother to her baby during pregnancy and result in stillbirth or serious birth defects.