Infectious diseases, also known as transmissible diseases or communicable diseases result from the infection, presence, and growth of pathogenic biological agents in an individual. These can be viruses or bacteria. In certain cases, infectious diseases may show no symptoms for much of their course or not at all. Transmission of a virus or bacteria can occur in various ways including physical contact, contaminated food, body fluids, objects, or airborne inhalation. Infectious diseases are sometimes called “contagious” when they are easily transmitted by contact with an ill person or their secretions. An infection is not the same as an infectious disease, as some infections do not cause illness.