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Chapter 18 Outline

Chapter 18 Outline - Chapter 18 Infection and Disease...

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Chapter 18 Infection and Disease Introduction 18.1 The Host-Microbe Relationship The Human Body Maintains a Symbiosis with Microbes Infection refers to the relationship between the host and microbe and the competition for supremacy between them If the host loses the competition, disease occurs Microbiota are microbes that reside in the body without causing disease (in symbiosis) In mutualism, both host and microbe benefit In commensalism, the microbe benefits and the host is unaffected Pathogens Differ in Their Ability to Cause Disease In parasitism, pathogens cause damage and disease in the host Pathogenicity refers to a microbe’s ability to enter a host and cause disease Virulence is the degree of pathogenicity Pathogenicity islands refers to gene clusters responsible for virulence Several Events Must Occur for Disease to Develop in the Host An exogenous infection occurs if a pathogen breaches the host’s external defense and enters sterile tissue An endogenous infection occurs if normal microbiota enter sterile tissue Opportunistic infections occur when commensals take advantage of a change in the body’s environment that favors the microbe Primary infections occur in otherwise healthy bodies Secondary infections occur in a body weakened by a primary infection Local diseases are restricted to a single area Systemic diseases disseminate to organs and systems Bacteremia is the dissemination of living bacteria through the bloodstream Septicemia is the multiplication of bacteria in the blood
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