MicroPara

• Microbes


  Too small to be seen with the unaided eye
• Prefix "path" or "patho-"


  Pertains to disease
• Pathogen


  A microbe capable of causing disease
• Pathology


  The study of the structural and functional manifestations of disease
• Pathologist


  A physician who has specialized in pathology
• Pathogenicity


  The ability to cause disease
• Pathogenesis


  The steps or mechanisms involved in the development of a disease
• Infection


  Colonization by a pathogen
• Infectious disease


  A disease caused by a microbe
• Many microbiologists reserve use of the word infection to mean colonization by a pathogen
• It is possible for a person to be infected with a certain pathogen, but not have the infectious disease caused by that pathogen
• Reasons why infection does not always occur

  • The microbe may land at an anatomic site where it is unable to multiply
  • Pathogens must attach to specific receptor sites before they are able to multiply and cause damage
  • Antibacterial factors that destroy or inhibit the growth of bacteria may be present at the site
  • The indigenous microbiota of that site may inhibit growth of the foreign microbe
  • The indigenous microbiota may produce antibacterial factors that destroy the newly arrived pathogen
  • The individual's nutritional and overall health status often influences the outcome
  • The person may be immune to that particular pathogen
  • Phagocytic white blood cells may engulf and destroy the pathogen before it has an opportunity to multiply, invade, and cause disease
• Four periods or phases in the course of an infectious disease

  1. Incubation period

  2. Prodromal period

  3. Period of illness

  4. Convalescence
• Incubation period


  The time that elapses between arrival of the pathogen and the onset of symptoms
• Convalescence


  Recovery period after illness
• Exposure to pathogen


  Initial contact with infectious agent
• Incubation period


  Time between exposure and onset of symptoms
• Prodromal period


  Time when patient feels "out of sorts" but does not yet experience actual symptoms
• Period of illness


  Time when patient experiences typical symptoms of the disease
• Disability


  Impairment caused by the disease
• Death


  End stage of disease progression
• Figure 14-1. Periods in the course of an infectious disease.
• Periods/phases of an infectious disease

  1. Incubation period

  2. Prodromal period

  3. Period of illness

  4. Convalescent period
• Factors affecting infectious disease progression

  • Immunocompetence of host
  • Virulence of pathogen
  • Number of pathogens entering body
• Localized infection


  Infection confined to one site
• Systemic/generalized infection


  Infection that has spread throughout the body
• Acute disease


  Rapid onset, relatively rapid recovery
• Subacute disease


  Sudden onset, but less sudden than acute, longer duration
• Chronic disease


  Insidious onset, long duration
• Symptom


  Subjective evidence of disease experienced by patient
• Sign


  Objective evidence of disease detected by healthcare provider
• Latent infection


  Disease that is lying dormant, not currently manifesting
• Stages of syphilis


  1. Primary

  2. Secondary

  3. Latent

  4. Tertiary
• Primary infection


  Initial infection caused by one pathogen
• Secondary infection


  Infection caused by a different pathogen following a primary infection
• Steps in pathogenesis of infectious diseases

  1. Entry of pathogen

  2. Attachment of pathogen

  3. Multiplication of pathogen

  4. Invasion/spread of pathogen

  5. Evasion of host defenses

  6. Damage to host tissues
• Virulent


  Capable of causing disease
• Avirulent


  Not capable of causing disease
• Toxigenic strains of Corynebacterium diphtheriae are virulent, whereas nontoxigenic strains are avirulent
• Encapsulated strains of Streptococcus pneumoniae can cause disease, but nonencapsulated strains cannot