ABSTRACT
This chapter deals with an overview of the different kinds of organisms that cause disease. It discusses the cell biology of infection and, finally, considers barriers to infection and innate immunity. The chapter also discusses some of the common features that microorganisms must have in order to be infectious. It explores the wide variety of organisms that are known to cause disease in humans. The chapter also deals with infectious disease are actually direct manifestations of the host's immune responses in action. It examines the mechanisms that pathogens use to control their hosts and the innate immune responses that hosts use to control pathogens. The chapter outlines the common strategies that many pathogens use to accomplish these tasks. Living at the expense of a host organism is a very effective strategy, and it is possible that every living organism on earth is subject to some type of infection.
