1. Microbe-Human Interactions

2. A Continuum of Interactions Exists • Routine Contact with Microorganisms • Infection – a condition in which pathogenic microbes penetrate host defenses, enter tissues and multiply • Disease – Deviation from Normal Health

3. The Normal State is that Humans are Host to a Variety of Microorganisms

4. Humans are Colonized from the Moment of Birth Babies Readily Acquire Flora During Delivery and from the External Environment

5. Regions that Host Flora • Skin • Oral cavity • Lower GI tract • Upper Respiratory • Genitourinary Tract

6. Skin Flora Staphylococcus, Micrococcus Propionibacterium

7. Flora of the Mouth and Pharynx Streptococcus, Neisseria, Staphylococcus, Lactobacillus, Bacteroides

8. Colonized Regions of the Respiratory Tract

9. Flora of the GI Tract Bacterioides, Lactobacillus, Enterococcus, Coliforms

10. Distribution of Flora

11. Flora of the Genitourinary Tract Lactobacillus, Streptococcus, E. coli, Staphylococcus

12. Maintenance of the Normal Resident Flora • Normal flora is essential to the health of humans • Flora create an environment that may prevent infections and can enhance host defenses • Antibiotics, dietary changes, and disease may alter flora • Probiotics – introducing known microbes back into the body

13. The Process of Disease

14. Types of Pathogens True vs. Opportunistic Pathogens

15. True Pathogens • Capable of causing disease in a healthy person • Generally associated with a recognizable disease • Can be weak to fatal in their effects

16. Opportunistic Pathogens • Cause disease in weakened host • Sometimes cause disease when they colonize a different region of the body • See Table 13.4 for pre-disposing conditions

17. Pathogenicity vs. Virulence • Pathogenicity = ability to cause disease • Virulence = relative capacity of a pathogen to invade and harm host cells

18. Gaining Access – Portal of Entry The Skin or Membrane Barrier through which Pathogens Gain Entry to the Body

19. Pathogens May be Exogenous or Endogenous

20. Some Agents that Enter the Skin • Staphylococcus aureus • Streptococcus pyogenes • Clostridium sp. • Insect-borne diseases • Hypodermic needle contaminants

21. GI Tract Entrants • Salmonella sp. • Vibrio sp. • E. coli • Shigella sp. • Entamoeba sp. • Giardia sp.

22. Respiratory Entrants • This is the most frequent route of entry • Streptococcus (Strep throat) • Influenza viruses • C. diptheriae • B. pertussis • Many others

23. Urogenital Entry Agents • Syphilis • Gonorrhea • Human Papilloma Virus • HIV • Chlamydia • Hepatitis B

24. Placental & Neonatal Agents STORCH = Syphilis, toxoplasmosis, others (hepatitis), rubella, cytomegalovirus, herpes simplex

25. Infectious Dose Minimum number of organisms required for an infection to be successful; lack of ID will not result in infection

26. To be Successful, a Pathogen Must • Adhere to the host • Penetrate host barriers • Establish a colony in host tissue

27. Some Methods of Adhesion • Fimbriae • Flagella • Adhesive Capsules • Binding to Receptors (Viruses)

28. Virulence factors Traits used by pathogens to invade and establish themselves in the host; also determine the degree of tissue damage that occurs

29. Some Virulence Factors • Extracellular Enzymes • Exotoxins • Endotoxins • Anti-phagocytic Factors

30. Exotoxins – Secreted by Living Cells Examples: Botulin Toxin, Hemolysins (Strep and Staph)

31. Endotoxins are Released by Dead Cells Example: Lipopolysaccharides from Gram- cells

32. Antiphagocytic Factors Ex.: Leukocidins, Slime Layers

33. The Process of Infection and Disease • Distinct stages of clinical infections: • incubation period - time from initial contact with the infectious agent to the appearance of first symptoms; agent is multiplying but damage is insufficient to cause symptoms; several hours to several years • prodromal stage – vague feelings of discomfort; nonspecific complaints • period of invasion – multiplies at high levels, becomes well established; more specific signs and symptoms • convalescent period – as person begins to respond to the infection, symptoms decline

34. Patterns of Infection • Localized - Contained • Systemic – Agent Circulates Freely • Focal – Localized infection breaks loose or attacks a distant target with toxin • Mixed – more than one agent invades

35. Temporal Patterns of Infection • Acute = short-lived but severe • Chronic = long-lived, persistent

36. Signs of Disease vs Symptoms • Signs = objective evidence of disease • Symptoms = subjective evidence sensed by patient (discomfort)

37. Some Signs of Infection • Inflammation • Skin lesions • Elevated WBC count • Bacteria or virus in blood

38. Portals of Exit for Pathogens • Respiratory/ Salivary • Skin • GI tract • Urogenital • Blood

39. Persistence of Infection • Latent infections & recurrent disease • Sequelae – long term damage to organs/tissues

40. Epidemiology The Study of Disease in Populations

41. Classifications of Diseases • Endemic – exhibits a relatively stable frequency in a particular location over time • Sporadic – occasional cases at irregular intervals • Epidemic – increase beyond what might be expected in a given population • Pandemic – spread of epidemics across continents

42. Patterns of Diseases

43. Pathogen Reservoirs vs Sources • Reservoir = habitat where the organism occurs • Source = Actual contact which provides the infection

44. Disease Carriers Shelter and Spread a Pathogen Inconspicuously

45. Carrier States • Asymptomatic – No signs of infection • Incubation – Spreads infection while it is incubating (still no symptoms) • Convalescent – Sheds microbes while recuperating • Chronic – Latent infections can be sheltered after apparent recovery • Passive – Mechanically picks up and transfers microbes

46. Disease Vectors Animals that transport an infection from one host to another

47. Biological Vectors • Actively participate in pathogen’s life cycle • Can inject infected saliva (mosquito) • May defecate around bite wound (flea) • Regurgitate blood into a wound (tsetse fly)

48. Mechanical Vectors Move the Pathogen from one Host to Another Without being Infected

49. Zoonosis An infection naturally found in animals, but transmissible to humans (See Table 13.10)

50. Communicable & Contagious Diseases • Communicable diseases can be transferred from one host to another and infection established • Contagious diseases are highly transmissible and move readily from host to host • Non-communicable diseases are not transmitted from one host to another