Encyclopedia of Infectious Diseases

Carol Turkington, Bonnie Ashby

From birth until death, the human body is under relentless attack by hordes of living organisms that compete for survival in our environment The air we breathe, the food we eat, the ground we walk on, the water we drink, the buildings we live in, the vegetation that surrounds us—all harbor infectious organisms. These agents of infectious disease come in all shapes and sires, from microscopic viruses, bacteria, and protozoans to foot-long parasitic worms. While these germs may vary wildly in appearance, they all share a depen-dence on human beings for at least part of their life cycle.