The term infectious disease covers a wide range of disorders that are caused by organisms, more commonly known as viruses, bacteria, parasites, or fungi. Our bodies are naturally home to many of these organisms, either inside of our bodies or on our skin. In most cases and for most of the time, they are harmless and can even be helpful. However, sometimes, and under certain conditions, some of these organisms can cause disease. Infectious diseases can be spread through a wide range of contact points, including person to person and also from insect bites, contact with animals, and the environment. Illnesses that fall under the term infectious disease includes common illnesses such as the common cold and influenza, to more severe and less common illnesses such as malaria, whooping cough, SARS, and tuberculosis. The list of infectious diseases is quite extensive, with many of them sharing similar symptoms like fever, cough, fatigue, diarrhea, and muscle aches.