However, disease is a constant threat to our health and life. Everyone has been affected by disease sometime in his or her life. Infectious bacteria, viruses, fungi, and protozoa have existed longer than the human species. Usually diseases are contained to small groups or areas. However, periodically a disease will spread out of control and rapidly infect a population.
Epidemics are a frightening but natural occurrence.
Some epidemics, such as the Bubonic Plague, can wipe out millions and spread around the world, becoming pandemics. With today's global travel, pandemics are more frightening because they can spread around the world more rapidly. The Wonders of Microbes, on the MicrobeWorld Web site, has more information on infectious diseases .