All of the following are true statements EXCEPT: Infectious diseases represent a battle between the host's nonspecific and specific immune defenses and the microbe's ability to penetrate and avoid those defenses The etiologic agents of human microbial diseases include members of various different groups of microbes, for example bacteria, fungi, protozoa, and viruses Infectious diseases of humans can be caused by microbes originating from outside the body; i.e., transmitted from other people, animals, or environmental sources, or from microbes living inside or upon the human body Some diseases are caused by exotoxins that are produced by bacteria in localized infections and travel through the blood to cause systemic (generalized) effects Systemic microbial diseases always involve invasion and destruction of tissues at the site of an infection, followed by microbial spread to distant body sites.