Infectious Diseases, Emerging and Reemerging diseases: Confronting Future Outbreaks
Infectious diseases are disorders caused by organisms — such as bacteria, viruses, fungi or parasites. Many organisms live in and on our bodies. They're normally harmless or even helpful, but under certain conditions, some organisms may cause disease. Some infectious diseases can be passed from person to person. Many infectious diseases, such as measles and chickenpox, can be prevented by vaccines. Frequent and thorough hand-washing also helps protect you from infectious diseases.
There are four main kinds of germs:
Bacteria - one-celled germs that multiply quickly and may release chemicals which can make you sick
Viruses - capsules that contain genetic material, and use your own cells to multiply
Fungi - primitive plants, like mushrooms or mildew