KEY TAKEAWAYS •
Diseases vary in their communicability and contagiousness.
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There are certain stages to an infectious disease.
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Bacteria have certain virulence factors that enhance adhesion, increase infectivity, and protect the bacterium from the immune system.
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Viruses exhibit increases in adhesion and antigenic shift that increase their ability to infect the host organism.
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Fungi have many virulence factors, including toxins, which cause symptoms in the host.
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Protozoans and helminths also have virulence factors that increase infectivity.
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Epidemiologists study infectious and noninfectious diseases.
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There are different types of sources of an infection, depending on when and where the source comes from and the infectiousness of the persons who get the disease.
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Observational studies are more ethical than experimental studies but they might not adhere to Koch’s postulates.
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