Â© 2013 WebMD, LLC. All rights reserved. The teeth are the hardest substances in the human body. Besides being essential for chewing, the teeth play an important role in speech. Parts of the teeth include: â¢ Enamel: The hardest, white outer part of the tooth. Enamel is mostly made of calcium phosphate, a rock-hard mineral. â¢ Dentin: A layer underlying the enamel.
While they are often used synonymously, the terms infectious disease and communicable disease do not have the same meaning. A communicable disease is an infectious disease that is easily spread from one human to another.
Communicable diseases are diseases that are caused by bacteria, virus, fungus, or parasites. They are spread from person to person, or animal to person, through direct or indirect contact. Pathogens. A pathogen is an infection causing agent (germ). Pathogens are the cause of communicable diseases. Bacteria, viruses, fungus, and parasites can all be pathogens. The most common pathogens are bacteria and viruses. Causative agent- This is the disease causing agent (bacteria, virus, fungus, parasite).