Some bacteria can evade the innate defenses and some

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some bacteria can evade the innate defenses and some adaptive defenses by remaining inside host cells Some Serum Resistant Bacteria postpone formation of MAC by interfering with activation of the complement system via the alternative pathway Mechanisms to prevent encounters with phagocytes include C5a peptidase and membrane degrading toxins Mechanisms to avoid recognition and attachment by phagocytes include capsules, M protein, and Fc receptors Mechanisms to survive within the phagocyte include escape from the phagosome, preventing phagosome-lysosome fusion, and surviving within the phagolysosome Mechanisms to avoid antibodies include IgA protease, antigenic variation, and mimicking self Damage to the Host: o Exotoxins: proteins that have very specific damaging effects may act locally or cause dramatic systemic effects Many can be grouped into categories such as neurotoxins, enterotoxins, or cytotoxins The toxic activity of A-B Toxins is mediated by the A subunit binding to specific cells is mediated by the B Subunit Membrane Damaging Toxins disrupt cell membranes either by forming pores or by removing the polar head group on phospholipids in the membrane Superantigens override the specificity of the T Cell response, causing systemic effects due to the massive release of cytokines o Symptoms associated with Endotoxin are due to vigorous host response Lipid A of lipopolysaccharide is responsible for its toxic properties Peptidoglycan and certain other components induce various cells to produce pro-inflammatory cytokines o The release of enzymes and toxic products from phagocytic cells can damage tissues Immune Complexes can cause kidney and joint damage Cross-reactive antibodies can result in an autoimmune response Mechanisms of Viral Pathogenesis: o Viruses attach to specific receptors on the target cell o Some viruses can avoid the effects of interferon and some can regulate apoptosis of the host cell To subvert the role of antibodies, some viruses transfer directly from cell to cell The surface antigens of some viruses change quickly outpace the production of antibodies Mechanisms of Eukaryotic Pathogenesis: o Fungi: saprophytes are generally opportunists while dermatophytes cause superficial infections of skin, hair, and nails The most serious fungal infections are caused by dimorphic fungi o Protozoa and Helminths: eukaryotic parasites attach to host cells via specific receptors and use a variety of mechanisms to avoid antibodies The extent and type of damage they cause varies tremendously
Chapter Nineteen: Epidemiology Epidemiologists: study the frequency and distribution of disease in order to identify its cause, source, and route of transmission o Focus on the rate of disease: Endemic: diseases that are constantly present in a population Epidemic: an unusually large number of cases in a population o Preventing susceptible people from coming in contact with a

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