Syphilis is caused by a bacteria which is transmitted by direct contact with the sore of the infected person during sex. This bacteria enters in to body the through mucous membranes or cut and abrasion in skin. This infection begins with formation of a sore on the genital area, mouth or any other part of the body. If syphilis is not treated on time then it can affect other organs of the body like brain, heart etc. Penicillin is drug of choice to treat syphilis.