A disease that is caused by a microorganism, such as a bacterium, virus, or parasite, that is not normally found in the body and is capable of causing infection. Some, but not all, infectious diseases are contagious, meaning they can spread from person to person. Other infectious diseases can spread from animals or insects to humans, but not from person to person. HIV is both infectious and contagious.
See Related Term(s): Contagious Disease