1. Principles of Disease and Epidemiology14
Principles of Disease and Epidemiology

3. State of balance of a complex system
Homeostasis
State of balance of a complex system
Maintenance of homeostasis is an indicator of good health
Unable to maintain homeostasis- disease

4. Infection- colonization of the body by pathogenic microorganisms
Definitions
Infection- colonization of the body by pathogenic microorganisms
also when a particular organism is found where it shouldn’t be. Ex. E.coli in urinary tract.
Infectious disease- due to pathogenic microorganisms or their products

5. Pathology- study of disease Pathogenesis- way that disease develops
Definitions
Pathology- study of disease
Pathogenesis- way that disease develops
Etiology- cause or agent of disease
Genetic - cystic fibrosis
Infectious – diptheria. Corynebacterium diphtheriae

6. Normal Microbiota or (Flora)
Permanent, colonizing microbes
1013 body cells vs bacterial cells
Protection by microbial antagonism
Competition
Antibiotics
Maintain environmental conditions

7. Figure 14.1 Representative normal microbiota for different regions of the body.

9. Opportunistic Microorganisms
Potentially pathogenic
Take advantage of weakened host
Ex. E. coli
Pneumocystis jirovecii
Neisseria meningitidis 10% of adults are carriers.

10. Etiology- the cause
B. anthracis – Koch Postulates.

11. Classification of Infectious Diseases
Alterations to homeostasis
Signs – objective changes; observable by physician
Symptoms – subjective changes like pain and malaise
Syndrome – group of signs and symptoms
Type of transmission
Communicable - chickenpox,
non-communicable - tetanus
Ex tetanus – lock jaw.
Ex influenza – headaches, stomach ache – not apparent to an observer.
Ex malaria –

12. Classification of Infectious Diseases
Frequency
Sporadic – typhoid,
Endemic – common cold or malaria
epidemic – AIDS, influenza
Pandemic – AIDS, influenza (involves the whole world)
Herd immunity – when many immune people exist.

13. Classification of Infectious Diseases
Severity and duration
Acute – rapid but short ex. influenza
Chronic – slow to develop, lasts long period ex. mono, tuberculosis, hepatitis B
Latent causative agent remains inactive and the becomes active ex. Shingles, caused by varicella virus (chicken pox).

14. Classification of Infectious Diseases
Affect on host
Localized - abcess
Systemic – spread throughout the body by blood or lymph, measles
Focal – disease is spread and then localizes, ex. Teeth then biofilm localizes on artificial heart valve.

15. Extent of Host Involvement
Sepsis: toxic inflammatory condition arising from the spread of microbes, especially bacteria or their toxins, from a focus of infection
Bacteremia: bacteria in the blood
Septicemia: also known as blood poisoning; growth of bacteria in the blood

16. Classification of Infectious Diseases
State of host
Primary (smallpox)
Secondary infection, (AIDS)
Subclinical – disease does not display signs or symptoms
ex. Typhoid Mary, polio.

17. Patterns of Disease Development

18. Reservoirs of Infection
Humans – carriers ex. AIDS, diptheria, typhoid, hepatitis, ebola, flu
Animals – zoonoses ex. Rabies (wild animals), lyme disease (ticks), ebola (bats)
Non-living – soil, water ex. Clostridium, Salmonella, Vibrio, anthrax

19. Mechanisms of Transmission
Contact – direct (touching, kissing, sex), indirect (fomite – utensils, toys, bedding), droplets
Vehicle – water, food, air, blood, drugs, needles, fluids.
Vectors
Biological (bites – like malaria) and mechanical (microbes carried on insect’s foot)

20. Specific for most pathogens Respiratory and GI tracts most common
Portals of Exit
Specific for most pathogens
Respiratory and GI tracts most common

21. Nosocomial Infections – 8th leading cause of death in US.
Presence of microbes
Compromised host
Chain of transmission

24. Table 14.4 Microorganisms Involved in Healthcare-Associated Infections

25. Microbial Mechanisms of Pathogenicity15
Microbial Mechanisms of Pathogenicity

27. Microbial Pathogenicity

28. Ability of a microbe to cause disease
Pathogenicity
Ability of a microbe to cause disease
Virulence is a measure of pathogenicity

29. Steps of Pathogenicity
To cause disease a pathogen must:
Gain entry
Adhere or penetrate
Evade host defenses
Damage tissue

30. The routes of infection
Portals of Entry
The routes of infection
Mucous membranes
Skin
Injection or puncture
Parenteral – punctures, wounds, splitting of the skin surgery, bites, cuts etc.

31. Entry is Only the First Step
Preferred portals of entry
Minimum dose- number of organisms required to cause disease (a threshold)
ID50 – infectious dose for 50% of populuation
LD50 – lethal dose of toxin for 50% of populuation

32. Numbers of Invading Microbes
Bacillus anthracis
Portal of Entry
ID50
Skin
10–50 endospores
Inhalation
10,000–20,000 endospores
Ingestion
250,000–1,000,000 endospores

33. Adherence
Adhesins and ligands- surface molecules bind specifically to host cell surfaces

35. Invasive factors aid in penetration and evasion of host defenses
Virulence Factors
Invasive factors aid in penetration and evasion of host defenses
Toxigenic factors are toxins that directly damage host tissues

36. Capsules Glycocalyx around the cell wall Impair phagocytosis
Streptococcus pneumoniae—pneumonia
Haemophilus influenzae—pneumonia and meningitis
Bacillus anthracis—anthrax
Yersinia pestis—plague
Waxy lipid (mycolic acid) resists digestion
Mycobacterium tuberculosis

37. Enzymes Coagulases: coagulate fibrinogen Kinases: digest fibrin clots
Ex. Staphs.
Kinases: digest fibrin clots
Hyaluronidase: digests polysaccharides that hold cells together
Collagenase: breaks down collagen
Ex. Clostridium helps spread gas gangrene
IgA proteases: destroy IgA antibodies
Ex. Neisseria meningitidis.

38. S. pyogenes - streptokinase
Applications of Microbiology 15.1b
S. pyogenes - streptokinase

39. Antigenic Variation
Pathogens alter their surface antigens (and antibodies are rendered ineffective)
Example – Influenza ---avoids secondary immune response (Memory cells) because it mutates every year.
-HIV highly mutable within the host – avoids antibodies and T-mediated responses.

40. Poisonous products transported by blood and/or lymph
Toxins
Poisonous products transported by blood and/or lymph
Local or systemic damage
Two primary types
Exotoxins and endotoxins

42. Products of normal metabolism Gram positive or gram negative bacteria
Exotoxins
Proteins
Products of normal metabolism
Gram positive or gram negative bacteria

43. Cytotoxins- kill or impair cells
Exotoxins
Cytotoxins- kill or impair cells
Neurotoxins- disrupt nerve impulse transmission
Enterotoxins- cause GI disorders
Hemolysins – membrane disrupting erthrocytes

44. Power of toxins Toxins LD50 Botulinum 0.03 ng/kg Shiga toxin 250 ng/kg
Staphylococcal enterotoxin
1350 ng/kg
LD50 – lethal dose of toxin for 50% of populuation

45. Gram negative cell walls Released on lysis of cells
Endotoxin (within)
Lipid A portion of LPS (endotoxins are lipolysaccharides, exotoxins are proteins)
Gram negative cell walls
Released on lysis of cells
Systemic signs (fever, chills, shock, and sometimes death)

46. Septic shock – decrease in blood pressure caused by bacteria
- endotoxins cause macrophages to release cytokines like
TNF. TNF changes permeability in capillaries. Loose fluid,
blood pressure plummets.

47. Washwater containing Pseudomonas was sterilized and used to wash cardiac catheters. Three patients developed fever, chills, and hypotension following cardiac catheterization. The water and catheters were sterile. Why did the patients show these reactions? How should the water have been tested?

48. Mitosis cell stops (cytocidal)
Viral Pathogenicity
Cytopathic effects- the characteristic changes to host cells resulting from viral infection
Mitosis cell stops (cytocidal)
Host cells are made to release their enzymes (cytocidal)
Inclusion bodies (used to detect rabies)

49. Fungi lack defined virulence factors.
Fungal Pathogenicity
Fungi lack defined virulence factors.
Candida albicans releases proteases to help attachment to cell membranes.
Some allergic responses and a few toxins (mycotoxin phallodin aka deathcap)

50. Protozoa and Helminths
Invasive and toxigenic and long lasting
ex. Plasmodium invades hosts cells, reproduce in cells and release toxins (waste products)
ex. Trypanosoma – uses antigenic variations, changes its antigens every two weeks.