ch5&6

• Five Kingdom Classification (Robert Whittaker)

  • Animalia
  • Plantae
  • Protista: single celled eukaryotes (algae, amoeba, euglena, paramecium, slime moulds, plasmodium, protozoans)
  • Fungi: fungus-like and related eukaryotic organisms (yeast, molds, mushrooms)
  • Monera (Prokaryotes)
• Microorganisms are found in the soil, in the water, and on plants and animals. Billions are found in humans on the skin and in both the nasal and intestinal tracts
• Although most microorganisms live in harmony with the human body, some—called pathogens—can infect the body and cause disease. Infectious diseases range from mild illnesses, such as a cold, to fatal illnesses, such as AIDS
• We occasionally encounter people or animals that are infected and thus expose ourselves to the pathogens of their diseases. Our environment is such that everyday we live with some risk of exposure to diseases
• Infectious disease process


  The interaction between the pathogenic microorganism, the environment, and the host
• Pathogens


  • Viruses (Influenza A, shingles, Hepatitis)
  • Bacteria (Lyme disease, Leptospirosis)
  • Fungi (Candidiasis, Aspergillosis)
  • Parasitic protozoan diseases (Malaria, Giardia, Toxoplasmosis)
  • Prions (Creutzfeldt-Jakob disease)
• Pathogens


  • Pathogenicity - ability to produce disease
  • Degree of virulence - severity or harmfulness
  • Invasiveness - tendency to spread
• Reservoir


  The principal habitat in which a pathogen lives, flourishes and can multiply
• Reservoir types


  • Humans (acute clinical cases, carriers)
  • Animals or insects
  • Environment
• Human carrier types


  • Incubatory carriers
  • Inapparent carriers
  • Convalescent carriers
  • Chronic carriers
• Any infectious disease that is transmitted under natural conditions from animal to human is referred to as zoonosis
• Portals of exit


  • Alimentary (vomiting, diarrhea, biting)
  • Genitourinary (sexual transmission)
  • Respiratory (coughing, sneezing, talking)
  • Skin (skin lesions)
  • Trans-placental (mother to fetus)
• Direct transmission


  Occurs when there is direct contact with the infectious agent
• Indirect transmission


  Can occur through animate mechanisms (fleas, ticks, flies, mosquitoes) or inanimate mechanisms (food, water, biological products, surgical instruments, airborne)
• Portals of entry


  • Inhalation (respiratory tract)
  • Absorption (mucous membranes)
  • Ingestion (gastrointestinal tract)
  • Inoculation (inoculation injury)
  • Introduction (insertion of medical devices)
• Susceptible host


  • Age
  • Presence of malnutrition or dehydration
  • Underlying chronic disease
  • Immobility
  • Medication disrupting or suppressing immune response
  • General resistance factors (mucous membranes, skin, cough reflex)
• The healthcare environment can expose patients to infection risks that they may not encounter elsewhere
• Understanding how infections become established, and how they are transmitted, is essential for effective infection prevention and control
• There are opportunities to break or disrupt the chain of infection at any link
• Ways to break the chain of infection

  • Cleaning hands frequently
  • Staying up to date on vaccines
  • Covering coughs and sneezes
  • Staying home when sick
  • Following rules for standard and contact isolation
  • Using personal protective equipment properly
  • Cleaning and disinfecting the environment
• Pathogenicity


  The capability of a microorganism to cause a disease in a host; an innate property
• Virulence


  The quantity of pathogenicity of a microbe or a measure of the ability of the microbe to cause disease, determined by invasiveness and toxigenicity
• To cause disease, pathogens must penetrate the host tissues and multiply, usually becoming localized and forming a small focus of infection
• Localization usually occurs within the lymph nodes, liver, spleen or kidney. From this area of infection microbes may pass into the bloodstream and set up the conditions of bacteremia (non multiplying bacteria in the blood stream) and septicemia (reproducing bacteria)
• Adhesion factor


  Specific virulence factors that enhance the ability of a microorganism to attach to the surface of mammalian cells
• Invasiveness


  The ability of a microorganism to invade human tissues and to reproduce or multiply within the cells and tissues of the human body
• Growth and survival enhancing factors

  The ability of bacteria to grow within the blood of the host by utilizing available iron
• Infective dose


  The amount or quantity of microorganisms required to produce disease symptoms in a host; the more virulent the microbe, the fewer the number needed
• Toxigenicity


  The ability of a microorganism to produce toxins
• Toxins


  Biological poisons that disrupt the normal functions of cells and are generally destructive to human cells and tissues
• Types of toxins


  • Endotoxin (lipopolysaccharide component of gram-negative bacterial cell wall)
  • Exotoxins (protein toxins produced by gram-negative and gram-positive pathogenic bacteria)
  • Neurotoxins (protein exotoxins that interfere with nervous system function)
  • Enterotoxins (stimulate gastrointestinal tract cells abnormally, causing inflammation)
  • Cytotoxins (protein exotoxins that kill cells by enzymatic attack or blocking essential cellular metabolism)
• Factors that can contribute to tipping the balance for or against microbial initiation of disease in a particular individual

  • Economic, medical and social factors
  • Genetics
  • Individual lifestyle choices
• Virtually any microorganism can cause disease under the right set of conditions
• When you are tired and run-down

  You are more prone to infection
• An infectious disease is as much the result of the failure of the human defense as it is the result of the special properties of pathogenic microorganisms
• Infectious dose


  Number of pathogens needed to establish a disease
• Factors that influence the infectious dose

  • Route of entry of the pathogen
  • State of the host defenses
• Characteristics of a compromised host

  • Malnutrition
  • Disease
  • Chemotherapy
  • Burns
  • Broken skin or mucous membrane
  • Suppressed immune system
  • Impaired cell activity
• Predisposing factors that affect the occurrence of disease

  • Gender
  • Genetic
  • Environment: Climate, weather, nutrition, lifestyle, age, fatigue, occupation, pre-existing illnesses or conditions and medications
• Disease condition


  A state in which the body does not function normally