Unit 10

• Microorganism


  An organism that is too small to be seen with the unaided eye
• Pathology


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


  The ability to cause disease
• Pathogenesis

  The mechanism or step involved in the development of the disease
• Pathologist


  A physician who has specialized in pathology
• Why infection does not always occur

  • The microbe may land on a different anatomic site where it cannot multiply
  • Pathogens must attach to specific receptor sites
  • Presence of antibacterial factors that destroy or inhibit growth of bacteria
  • Presence of indigenous microflora that produce antibacterial factors
  • Individual resistance to infection, particularly previous exposure or vaccination
  • The person's health and nutritional status
  • Phagocytic WBCs may engulf or destroy the pathogen before it can multiply, invade and cause a disease
• Four Periods/Phases in the Course of an Infectious Disease

  • Incubation period
  • Prodromal Period
  • Period of Illness
  • Convalescent period
• Incubation period


  The period between the arrival of the pathogen and the onset of symptoms
• Prodromal Period


  The time when the patient feels something bad in their system, but is not yet experiencing the actual symptoms
• Period of Illness


  The time which the patient is experiencing the typical symptoms of the disease
• Convalescent period


  The time of recovery or healing
• Types of Infections


  • Local or localized
  • Systemic or generalized
• Local or localized infection


  Infection remains localized in one site of the body
• Local or localized infections

  • Pimples, boils and abscesses
• Systemic or generalized infection

  The infection spreads throughout the body
• Systemic or generalized infection


  • Mycobacterium Tuberculosis spreading from lungs to intestine
• Description of a Disease

  • Acute disease
  • Chronic disease
  • Subacute disease
• Acute disease


  Rapid onset and followed by a rapid recovery
• Acute diseases


  • Flu, mumps and measles
• Chronic disease


  Slow/insidious onset and lasts a long time
• Chronic diseases


  • Tuberculosis, leprosy and syphilis
• Subacute disease


  Comes on more suddenly than chronic disease, but less suddenly than acute disease
• Subacute disease


  • Bacterial endocarditis
• Clinical Manifestations of a Disease

  • Symptom
  • Sign
• Symptom


  Some evidence of a disease that is experienced or perceived by the patient
• Symptoms


  • Pain, tinnitus, blurred vision
• Sign


  Some type of objective evidence of a disease
• Signs


  • Vital signs, lump, laboratory studies
• Latent Infection


  An infectious disease that has symptoms for a period of time then becomes asymptomatic
• Latent Infections


  • Herpes - cold sores, fever
  • Syphilis - chancre
• Stages of Syphilis


  1. Syphilis infection (3 weeks)

  2. Primary: chancre (2-6 months)

  3. Secondary: rash, lesions, fever, hair loss (2-6 months)

  4. Latent stage: No symptoms (5-50 years)

  5. Tertiary: Destruction of brain, heart, spinal cord and other organs
• Primary versus Secondary Infection

  • Primary Infection - the first disease affecting the patient
  • Secondary Infection - the second disease resulting from the first disease affecting the patient
• Steps in the Pathogenesis of Infectious Diseases

  • Entry
  • Attachment
  • Multiplication
  • Invasion or spread
  • Evasion of host defenses
  • Damage of the host tissue or organs
• Virulence


  The degree to which a microorganism can cause disease
• Virulence Factors

  • Attachment
  • Receptors and Adhesin
  • Pili (Bacterial Fimbriae)
  • Obligate Intracellular Pathogens
  • Facultative Intracellular Pathogens
  • Capsules
  • Flagella
  • Exoenzymes (kinases, coagulase, hymolysins, necrotizing enzymes, lecithinase)
  • Toxins (Endotoxins, Exotoxins)