Sexually transmitted diseases (STDs) are illnesses transmitted by sexual contact. STDs comprise a large and diverse set of disease entities which include viruses, bacteria, protozoa, and arthropods. Many of these diseases can cause great harm before symptoms are detected. | Sexually transmitted diseases (STDs) are illnesses transmitted by sexual contact. STDs comprise a large and diverse set of disease entities which include viruses, bacteria, protozoa, and arthropods. Many of these diseases can cause great harm before symptoms are detected. |