Why We Get Sick: Chapter 3

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Why We Get Sick Chapter 3

• Signs and Symptoms of Infectious Disease

By Derek Caplan
Book By R.M. Nesse and G.C. Williams
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Types of Host Defenses

• Hygiene
• The Skin
• Pain and Malaise
• Expulsion-Based Defense
• Defense Mechanisms

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Hygiene

• Best defense Avoidance of danger
• Tend to avoid substances and people who may be a
  source of contagion
• Feces and vomit
• Tendency to defecate away from others
• Social pressures may protect us from infection by
  others

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The Skin

• like a wall around an ancient city
• Provides superior protection
• Parasites
• Mechanical, thermal, and chemical forces
• Pathogens cannot penetrate the skin
• Adjustable armor
• Hygiene helps maintains the skins barrier

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Pain and Malaise

• An adaptation that works with the skin to cause
  avoidance and escape
• Continued pain is adaptive, use of damaged tissue
  compromises effectiveness of adaptations
• tissue reconstruction, antibody response to
  bacteria
• Aches and pains are adaptive
• Encourage inactivity
• Encourages effective immune responses and repair
  of damaged tissue

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Expulsion-Based Defense

• All bodily openings provide possible entrance for
  pathogens
• Sneezing- a defensive adaptation
• Coughing
• Nausea and Vomiting
• Diarrhea
• Urinary Tract and Reproductive System

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Defense Mechanisms

• Macrophages
• Helper T Cells
• Major Histocompatibility Complex (MHC)
• ID card
• Immune system
• inflammation and specialized antibodies

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Host Adaptation

• FeverBeneficiary?
• Decreasing a fever when sick may cause one to
  heal more slowly
• Withhold iron when sick?
• Taking iron supplements when sick may cause death
• High iron foods seem disgusting to us when sick

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Pathogen Strategies

• Evasion of Defenses
• Attack on Defenses
• Vector Transmission
• Host Manipulation

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Evasion of Defenses

• Door-to-Door Salesman Tactic
• Rabies, neurotransmitter Epstein-Barr, C4
  receptor
• Evasion of Immune System
• African sleeping sickness, trypanosome changes
  disguises
• Malarial Parasites, bind to walls of blood
  vessels
• Spy Tactic
• Some bacteria and worms have very similar
  external chemistry to human cells, difficult to
  differentiate

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Attack on Defenses

• Pathogens seek not only to evade, but to use
  their own weaponry to gain the upper-hand
• Staphylococcus aureus, blocks useful inflammation
  
• Streptococcal infection secretes streptolysin-O,
  kills white blood cells
• Some bacteria cause shock caused by the formation
  of of lipopolysaccharide (LPS)

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Vector Transmission and Host Manipulation

• Diseases may be spread through vector
  transmission by insects, carrying transport
  agents.
• Malaria is a well known pathogen, spread by
  Mosquitoes.
• Parasites have adapted to use the host as they
  want, called host manipulation
• Rabies Virus

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Conclusion

• Host organisms have developed a number of
  defenses against pathogens
• Pathogens have developed a number of strategies
  against the defenses of the host
• weapons of both parties are growing, leading to
  an arms race without end (Chapter 4)

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