Syphilis, gonorrhoea and genital warts as STD caused by Treponema pallidum, Neisseria gonorrhoeae and human papillomavirus. These pathogens directly infect and damage sex organs causing itching, fluid discharge, slight pain and swelling of genitalia. AIDS (Acquired Immuno Deficiency Syndrome) is a set of symptoms caused by HIV virus in humans. It is transmitted through sexual contacts from infected to healthy person. The HIV virus does not directly affect sex organs as such but produce other set of symptoms in the body of infected person.