Microbial Pathogenesis

• Disease def:


  normal functions of the body are damaged or impaired
• Infection def:

  successful colonization of a host by a microorganism (pathogen)
• Symptoms def:


  felt or experience by patient (nausea, loss of appetite, pain)
• Signs def:


  Measurable (fever, breathing, heart rate)
• Pathogenicity def:


  potential ability to cause disease (qualitative)
• Virulence def:


  disease producing power, degree of pathogenicity (quantitative)
• Pathogens and viruses with high pathogenicity and high virulence?

  Can have low infectious doses (ID) and low lethal doses (LD), meaning they can use infection and severe disease with only a small number of microorganisms or toxin exposure
• Pathogens and viruses with low pathogenicity and low virulence?

  Can have high infectious doses (ID) and high lethal doses (LD), requiring a larger inoculum or toxin exposure to cause infection or death
• What are the principal portals of entry?

  Mucus membranes (placenta, respiratory tract)

  Skin

  parental route (bite, puncture, injection)
• Communicable disease def:


  contagious diseases - easily spread from person to person
• Non-communicable disease def:


  not spread from person to person
• Iatrogenic disease def: 


  diseases contracted as the result of a medical procedure
• Nosocomial disease def:


  Disease acquired in hospital settings
• Zoonotic disease def:


  transferred from animals to humans
• Stages of an acute infectious disease

  1. incubation period

  2. prodromal period

  3. period of illness

  4. period of decline

  5. period of covalescence

  Unimodal shape for signs and symptoms and number of particles present
• Acute disease def:


  short time and involves a rapid onset of disease conditions
• Chronic disease def:


  long time
• Latent disease def:


  pathogen goes dormant for extended periods of time w/ no active replications
• Koch's postulate 


  Summary

  1. Microorganisms (agents) must be present in every case of the disease by absent from healthy individuals
  2. Microorganisms must be isolated from the diseased individual and grown in pure culture
  3. The pure culture of the microorganism must cause the disease when inoculated into a healthy susceptible host
  4. Microorganism must be re-isolated from the experimentally infected host and shown to be the same as the original pathogen
• Limitations to Kock's postulate

  -Inapplicability to all diseases

  -Ethical considerations

  -Complexity of host-pathogen interactions

  -Chronic and polymicrobial infections
• Primary pathogen def:


  cause disease in a host regardless of the host's resident microbia or immune system

  ex. tuberculosis, pneumonia, malaria
• Opportunistic pathogen def:


  only cause disease in situations that compromise the host's defenses

  ex. bacterium found in soil and water, fungus, yeast
• Stages of pathogenesis:


  -1. Adhesion: pathogenic microbes attach to the cells of the body

  -2. Invasion: dissemination of pathogen throughout the tissues/body.

  -may produce exoenzymes/toxins = colonize and damage host tissue as they spread deeper into the body

  -3. Infection: successful multiplication of pathogen

  -local: confined to a small area, near the entry

  -focal: localized pathogen, or toxins produced

  - systemic: infection becomes disseminated
• Roles of exit and entry in the transmission of disease?

  To allow diseases to enter and exit the body.

  -Entry: skin

  -Exit: same place or respiratory tract (coughing), gastrointestinal (feces, saliva), genitourinary (urine, secretions), blood (needles, syringes)
• Explain how specific traits of pathogens that contribute to their ability to cause disease and evade the host's immune defenses

  -1. Adhesion and colonization: allow invasion of the host's immune system

  -2. Invasion and tissue damage: production of toxins or enzymes that disrupt cellular structures, induce cell death or interfere with normal physiological functions

  -3. Evasion of host immune response: interferes with ability to fight infection

  -4. Systemic effects: affects organ systems, toxins into bloodstream, sepsis
• Endotoxins: 


  proteins produced and secreted by bacteria, produced inside cell and released
• Exotoxins:


  lipid portion, produced outside of cell and released
• Cytopathic effects of viruses

  Visible effects of viral infection on a cell

  • stopping cell synthesis
  • causing cell lysosomes to release enzymes
  • creating inclusion bodies in cell cytoplasm
  • changing host cell function