MBI 111 Microorganisms and Human Disease

Principles of Disease, Microorganisms as Parasitic Agents and Epidemiology

Infectious Disease Principles

Disease Definitions

• Host -

• Parasite -

• Disease -

• Infectious disease -

• Pathogen -

• Virulence -

Koch's Postulates

If a microorganism is the causative (etiologic) agent of an infectious disease, it must be:

• Present -

• Isolated -

• Able to Cause -

• Re-isolated -

Steps in Pathogenesis

To cause disease, a pathogen must:

• Contact -

• Colonize -

• Infect -

• Evade -

• Damage -

Virulence Factors

Factors responsible for the virulence of a microorganism because they influence its ability to cause disease by affecting its invasiveness and/or its toxigenicity

• Adhesins -

• Invasins -

• Evasins -

• Toxins -

Microorganisms

Comparison of Eukaryotes, Prokaryotes, and Viruses

• prokaryotes -

   

• eukaryotes -

   

• viruses -

   

Bacteria

• morphology
  • cytoplasmic membrane -

     

  • cell wall -

     

  • capsule -

     

  • ribosomes -

     

  • chromosome -

     

  • plasmids -

     

  • granules -

     

  • flagella -

     

  • pili -

     

  • endospore -

     

• growth
  • proliferate by binary fission

     

  • growth curve - phases:
    • lag -

       

    • log -

       

    • stationary -

       

    • death -

       

  • nutritional requirements
    • chemical
      • water -

         

      • essential elements - C, H, O, N, P, S

         

      • trace elements - Ca, Mg, Fe, Na, K, Zn, Co, Mn, plus others

         

      • organic growth factors - vitamins, etc.

         

    • physical
      • temperature -

         

      • oxygen -

         

      • pH -

         

      • salts -

         

• importance and habitat -

   

Viruses

• morphology
  • nucleocapsid
    • nucleic acid -

   

•  
• capsid -

 

 

• envelope -

   

 

• growth - viral replication includes these steps:
  • attachment -

     

  • penetration -

     

  • uncoating -

     

  • synthesis -

     

  • maturation -

     

  • release -

     

• importance and habitat -

   

Fungi

• morphology
  • single cells or filamentous (mycelial) colonial forms -
    • yeasts -

     

    • moulds -

     

  • cytoplasmic membrane -

     

  • cell wall -

     

  • capsule -

     

  • chromosomes -

     

• growth
  • proliferate by:
    • binary fission -

       

    • budding -

       

    • spores -

       

  • nutritional requirements
    • chemical
      • water -

         

      • essential elements - C, H, O, N, P, S

         

      • trace elements - Ca, Mg, Fe, Na, K, Zn, Co, Mn, plus others

         

      • organic growth factors - vitamins, etc.

         

    • physical
      • temperature -

         

      • oxygen -

         

      • pH -

         

      • salts -

         

• importance and habitat -

   

Protozoa

• morphology

   

  • cytoplasmic membrane -

     

  • cell wall -

     

  • contractile vacuoles -

     

  • ribosomes -

     

  • chromosomes -

     

  • pseudopodia vs. undilipodia -

     

  • cysts -

     

• growth
  • proliferate by:
    • binary fission -

       

    • budding -

       

    • zygote formation -

       

  • nutritional requirements
    • water -

       

    • essential elements - C, H, O, N, P, S

       

    • trace elements - Ca, Mg, Fe, Na, K, Zn, Co, Mn, plus others

       

    • organic growth factors - vitamins, etc.

       

  • physical
    • temperature -

       

    • oxygen -

       

    • pH -

       

    • salts -

       

• importance and habitat

   

Helminths

• morphology
  • multicellular eukaryotes with organ systems

     

    • cytoplasmic membrane -

       

    • cell wall -

       

    • ribosomes -

       

    • chromosomes -

       

  • flatworms vs. roundworms:
    • flatworms -

       

      • Trematodes

         

      • Cestodes

         

    • roundworms - Nematodes

       

  • holdfasts -

     

• growth
  • proliferate by:
    • zygote formation -

       

    • complicated life-cycles -

       

  • nutritional requirements
    • water -

       

    • essential elements - C, H, O, N, P, S

       

    • trace elements - Ca, Mg, Fe, Na, K, Zn, Co, Mn, plus others

       

    • organic growth factors - vitamins, etc.

       

  • physical
    • temperature -

       

    • oxygen -

       

    • pH -

       

    • salts -

       

• importance and habitat -

   

Virulence Factors

Adhesins

• pili -

   

• capsules -

   

• hemagglutinins -

   

• spikes (peplomers) -

   

• holdfasts -

   

• unknown mechanisms -

   

Invasins

• fibrinolysin -

   

• hyaluronidase -

   

• hemolysins -

   

Evasins

• pili -

   

• capsules -

   

• catalase -

   

• coagulase -

   

• M protein -

   

• leukocidins -

   

• anti-phagosomal factors -

Toxins

• toxic molecules produced by bacteria and fungi include:
  • exotoxins
    • bacterial examples
      • botulin -

      • tetanospasmin -

      • enterotoxin -

      • diphtheria toxin -

    • fungal example - gliotoxin

  • endotoxin -

• animal viruses - consequences of virus infection of a animal host cell include:
  • Lytic infection -

  • Persistent infection -

  • Latent infection -

  • Transformation -
    • benign tumor -

    • malignant (metastatic) tumor -

• protozoa can be directly toxic to cells -

• toxicity can also be triggered by viruses and other intracellular parasites

• damage or toxicity can be triggered as a result of an inappropriate immune response by the host

Epidemiology

Definitions

• Epidemiology -

• Epidemic -

• Prevalence -

• Incidence -

• Pandemic -

• Endemic -

• Outbreak -

• Morbidity -

• Mortality -

• Reservoir -

• Carrier -

• Zoonoses -

• Vector -

• Fomite -

Transmission of Infectious Diseases

• Stages in transmission -

• Modes of transmission -

Types of Epidemics

• Common-source -

• Propagated -

Introduction of New Pathogens into Susceptible Populations

• Rapid onset of epidemics -

• Importance to natives -

Nosocomial Infections

• Iatrogenic infection -

• Transmission -

• Crowding -

• Immunocompromise -

• Antibiotic-resistance -

Public Health Measures for Control of Epidemics

• Immunization -

• Blocking vehicle-mediated transmission -

• Quarantine -

• Elimination of animal reservoirs -

Global Health Considerations

• Industrial vs. "developing" countries -

• Travel to endemic areas -