The worlds common diseases or medical conditions are abnormal conditions of an organism that impairs bodily functions associated with specific symptoms and signs.This may be caused by many external factors such as infectious disease or caused by internal dysfunctions such as autoimmune diseases.With human beings, "disease" is often used more widly to refer to a condition that causes pain, dysfunction, distress, social problems, and sometimes death to the person afflicted, or similar problems for those in contact.