Pathogenesis & Virulence of Infectious Diseaseswou.edu/~guralnl/gural/318pathogenesis.pdf ·...
Transcript of Pathogenesis & Virulence of Infectious Diseaseswou.edu/~guralnl/gural/318pathogenesis.pdf ·...
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Pathogenesis & Virulence of Infectious Diseases
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Why Exposure May NOT Lead to Infection
• Agent lands in/on wrong body part• Host cells lacks specific receptors• Antimicrobial compound destroys pathogen• Normal flora outcompetes or kills pathogen• Host immune system destroys pathogen
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PathogenesisSteps involved in the development of disease
Infection: colonization by a microorganism
Primary, SecondaryIncubation: pathogen
arrival to symptomsProdromal: early
symptoms, usually general
Illness: typical disease-specific symptoms
Convalescence: recovery or disease regress
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Common Steps of InfectionEntry: contact, injection, inhalation…Attachment: pathogen sticks to cells in bodyMultiplication: growth - leading, possibly, to…
Variable Steps of InfectionInvasion: localized to systemic, related to…Evasion: pathogen hides from immune system Damage: pathogen AND/OR host-mediated
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Kinds of Diseases/InfectionsAcute: rapid onset and recovery. Sub-acuteChronic: slow onset and recoveryLatent: cycles of symptoms, no symptoms
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Virulence FactorsPathogen traits that cause infection and disease
Some Facilitate Attachment
Surface Proteins: bind to host cell receptors
Pili/Fimbrae: bind to host epithelial surfaces
Capsules: bind to host epithelial surfaces
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Some Facilitate InvasionFlagella: allows pathogen to moveFibrinolysin: “clot-busters,” digest fibrinFlesh-Eating Enzymes: burrow into tissuesCoagulase: coat self with host fibrin
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Extracellar enzymes
• Hyaluronidase -connective tissue
• Collagenase -collagen
• Lecithinase -muscle, membranes
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Hemolysins
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Many also serve to evade the immune system.
Some Facilitate EvasionIntracellular Growth: hide IN cells undetectedAntiphagocytic: capsules, flagella, waxy wallsAg Variation: changing surface gene productsMimicry: look like host, autoimmune problems
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Evasion
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Some Facilitate Damage
Some Facilitate DamageEndotoxins: LPS proteins, less damagingExotoxins: secreted proteins, more
damagingHemolysin: lyse RBC, release iron for
growth
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