Chapter 14

1. Chapter 14 Infection, Infectious Diseases, and Epidemiology

2. Symbiotic Relationships Between Microbes and Their Hosts Symbiosis means “to live together” We have symbiotic relationships with countless microorganisms Types of symbiosis Mutualism Commensalism Parasitism © 2012 Pearson Education Inc.

3. Table 14.1 The Three Types of Symbiotic Relationships

4. Figure 14.1 Mutualism as shown by wood-eating termites

5. Symbiotic Relationships Between Microbes and Their Hosts Normal Microbiota in Hosts Also termed normal flora and indigenous microbiota Organisms that colonize the body’s surfaces without normally causing disease Two types Resident microbiota Transient microbiota © 2012 Pearson Education Inc.

6. Figure 14.2 Normal microbiota of the human nasal cavity

7. Symbiotic Relationships Between Microbes and Their Hosts Normal Microbiota in Hosts Resident microbiota Are a part of the normal microbiota throughout life Are mostly commensal © 2012 Pearson Education Inc.

8. Table 14.2 Some Resident Microbiota

9. Symbiotic Relationships Between Microbes and Their Hosts Normal Microbiota in Hosts Transient microbiota Remain in the body for short period Found in the same regions as resident microbiota Cannot persist in the body Competition from other microorganisms Elimination by the body’s defense cells Chemical or physical changes in the body © 2012 Pearson Education Inc.

10. Symbiotic Relationships Between Microbes and Their Hosts Normal Microbiota in Hosts Acquisition of normal microbiota Development in womb free of microorganisms (axenic) Microbiota begin to develop during birthing process Much of one’s resident microbiota established during first months of life © 2012 Pearson Education Inc.

11. Symbiotic Relationships Between Microbes and Their Hosts How Normal Microbiota Become Opportunistic Pathogens Opportunistic pathogens Normal microbiota that cause disease under certain circumstances Conditions that provide opportunities for pathogens Introduction of normal microbiota into unusual site in body Immune suppression Changes in the normal microbiota © 2012 Pearson Education Inc.

12. Reservoirs of Infectious Diseases of Humans Most pathogens cannot survive for long outside their host Reservoirs of infection Sites where pathogens are maintained as a source of infection Three types of reservoirs Animal reservoirs Human carriers Nonliving reservoirs © 2012 Pearson Education Inc.

13. Reservoirs of Infectious Diseases of Humans Animal Reservoirs Zoonoses Diseases naturally spread from animal host to humans Acquire zoonoses through various routes Direct contact with animal or its waste Eating animals Bloodsucking arthropods Humans are usually dead-end host to zoonotic pathogens © 2012 Pearson Education Inc.

14. Reservoirs of Infectious Diseases of Humans Human Carriers Infected individuals who are asymptomatic but infective to others Some individuals eventually develop illness while others never get sick Healthy carriers may have defensive systems that protect them © 2012 Pearson Education Inc.

15. Reservoirs of Infectious Diseases of Humans Nonliving Reservoirs Soil, water, and food can be reservoirs of infection Presence of microorganisms often due to contamination by feces or urine © 2012 Pearson Education Inc.

16. The Movement of Microbes into Hosts: Infection Exposure to Microbes: Contamination and Infection Contamination The mere presence of microbes in or on the body Infection When organism evades body’s external defenses, multiplies, and becomes established in the body © 2012 Pearson Education Inc.

17. The Movement of Microbes into Hosts: Infection Portals of Entry Sites through which pathogens enter the body Four major pathways Skin Mucous membranes Placenta Parenteral route © 2012 Pearson Education Inc.

18. Ear Figure 14.3 Routes of entry for invading pathogens Brokenskin Insectbite Conjunctivaof eye Nose Mouth Placenta Vagina Anus In males:Penis Urethra

19. The Movement of Microbes into Hosts: Infection Portals of Entry Skin Outer layer of dead skin cells acts as a barrier to pathogens Some pathogens can enter through openings or cuts Others burrow into or digest outer layers of skin © 2012 Pearson Education Inc.

20. Sebaceous(oil) gland Hair Figure 14.4 A cross-section of skin Pore ofsweat duct Bloodcapillaries Epidermis Nerve fiber Dermis Nerve ending Vein Artery Sweatgland Fat cells Hairfollicle

21. The Movement of Microbes into Hosts: Infection Portals of Entry Mucous membranes Line the body cavities that are open to the environment Provide a moist, warm environment hospitable to pathogens Respiratory tract is the most common site of entry Entry is through the nose, mouth, or eyes Gastrointestinal tract may be route of entry Must survive the acidic pH of the stomach © 2012 Pearson Education Inc.

22. The Movement of Microbes into Hosts: Infection Portals of Entry Placenta Typically forms effective barrier to pathogens Pathogens may cross the placenta and infect the fetus Can cause spontaneous abortion, birth defects, premature birth © 2012 Pearson Education Inc.

23. The Movement of Microbes into Hosts: Infection Portals of Entry Parenteral route Not a true portal of entry Means by which the portal of entry can be circumvented Pathogens deposited directly into tissues beneath the skin or mucous membranes © 2012 Pearson Education Inc.

24. The Movement of Microbes into Hosts: Infection The Role of Adhesion in Infection Process by which microorganisms attach themselves to cells Required to successfully establish colonies within the host Uses adhesion factors Specialized structures Attachment proteins © 2012 Pearson Education Inc.

25. Figure 14.5 The adhesion of pathogens to host cells-overview

26. The Movement of Microbes into Hosts: Infection The Role of Adhesion in Infection Attachment proteins help in adhesion Found on viruses and many bacteria Viral or bacterial ligands bind host cell receptors Interaction can determine host cell specificity Changing/blocking a ligand or its receptor can prevent infection Inability to make attachment proteins or adhesins renders microorganisms avirulent Some bacterial pathogens attach to each other to form a biofilm © 2012 Pearson Education Inc.

27. Figure 14.6 Dental plaque

28. The Nature of Infectious Disease Infection is the invasion of the host by a pathogen Disease results if the invading pathogen alters normal body functions Disease is also referred to as morbidity © 2012 Pearson Education Inc.

29. The Nature of Infectious Disease Manifestations of Disease: Symptoms, Signs, and Syndromes Symptoms Subjective characteristics of disease felt only by the patient Signs Objective manifestations of disease observed or measured by others Syndrome Symptoms and signs that characterize a disease or abnormal condition Asymptomatic, or subclinical, infections lack symptoms but may still have signs of infection © 2012 Pearson Education Inc.

30. The Nature of Infectious Disease Causation of Disease: Etiology Study of the cause of disease Germ theory of disease Disease caused by infections of pathogenic microorganisms Robert Koch developed a set of postulates to prove a particular pathogen causes a particular disease © 2012 Pearson Education Inc.

31. Agent not typically foundin healthy subjects The suspected agent must be presentin every case of the disease. Diseased subjects Healthy subjects Figure 14.7 Koch’s postulates Petri plate Bacterialcolonies The agent must beisolated and grownin pure culture. Streaked plates Injection The cultured agent must causethe disease when it is inoculatedinto a healthy, susceptibleexperimental host (animal or plant). The same agent mustbe reisolated from thediseased experimentalhost.

32. The Nature of Infectious Disease Causation of Disease: Etiology Exceptions to Koch’s postulates Some pathogens can’t be cultured in the laboratory Diseases caused by a combination of pathogens and other cofactors Pathogens that require a human host Difficulties in satisfying Koch’s postulates Diseases can be caused by more than one pathogen Pathogens that are ignored as potential causes of disease © 2012 Pearson Education Inc.

33. The Nature of Infectious Disease Virulence Factors of Infectious Agents Pathogenicity Ability of a microorganism to cause disease Virulence Degree of pathogenicity Virulence factors contribute to virulence Adhesion factors Biofilms Extracellular enzymes Toxins Antiphagocytic factors © 2012 Pearson Education Inc.

34. More virulent Francisella tularensis(rabbit fever) Figure 14.8 Relative virulence of some microbial pathogens Yersinia pestis(plague) Bordetella pertussis(whooping cough) Pseudomonas aeruginosa(infections of burns) Clostridium difficile(antibiotic-induced colitis) Candida albicans(vaginitis, thrush) Lactobacilli, diphtheroids Less virulent

35. The Nature of Infectious Disease Virulence Factors of Infectious Agents Extracellular enzymes Secreted by the pathogen Dissolve structural chemicals in the body Help pathogen maintain infection, invade, and avoid body defenses © 2012 Pearson Education Inc.

36. Figure 14.9a Some virulence factors: Extracellular enzymes Hyaluronidase and collagenase Coagulase and kinase Bacterium Bacterium Hyaluronidase Coagulase Clot Clottingprotein Kinase Epithelialcells Collagenase Collagen layer Bacteria producehyaluronidase andcollagenase. Invasive bacteriareach epithelialsurface. Bacteria producecoagulase. Clot forms. Bacteria later producekinase, dissolving clotand releasing bacteria. Bacteria invade deeper tissues. Extracellular enzymes

37. The Nature of Infectious Disease Virulence Factors of Infectious Agents Toxins Chemicals that harm tissues or trigger host immune responses that cause damage Toxemia refers to toxins in the bloodstream that are carried beyond the site of infection Two types Exotoxins Endotoxins © 2012 Pearson Education Inc.

38. Figure 14.9b Some virulence factors: Toxins Exotoxin Endotoxin Bacterium Exotoxin Phagocyte PhagocytizedGram bacteria Exocytosis Endotoxin Dead Grambacteria Blood vessel Cytotoxin kills host’s cells. Bacteria secrete exotoxins, in thiscase a cytotoxin. Dead Gram-negative bacteria release endotoxin (lipid A), which induceseffects such as fever, inflammation, diaarrhea, shock, and blood coagulation. Toxins

39. The Nature of Infectious Disease ANIMATION Virulence Factors: Exotoxins © 2012 Pearson Education Inc.

40. The Nature of Infectious Disease ANIMATION Virulence Factors: Endotoxins © 2012 Pearson Education Inc.

41. The Nature of Infectious Disease Virulence Factors of Infectious Agents Antiphagocytic factors Factors prevent phagocytosis by the host’s phagocytic cells Bacterial capsule Composed of chemicals not recognized as foreign Slippery Antiphagocytic chemicals Prevent fusion of lysosome and phagocytic vesicles Leukocidins directly destroy phagocytic white blood cells © 2012 Pearson Education Inc.

42. Figure 14.9c Some virulence factors: Antiphagocytic factors Incomplete phagocytosis Phagocytosis blocked by capsule Capsule aroundbacterium Capsule aroundbacterium Bacteria reproduce Phagocyticvesicle Phagocyte Lysosome Antiphagocytic factors

43. The Nature of Infectious Disease ANIMATION Virulence Factors: Hiding from Host Defenses © 2012 Pearson Education Inc.

44. The Nature of Infectious Disease The Stages of Infectious Disease The disease process occurs following infection Many infectious diseases have five stages following infection Incubation period Prodromal period Illness Decline Convalescence © 2012 Pearson Education Inc.

45. Figure 14.10 The stages of infectious diseases Prodromalperiod(vague,generalsymptoms) Incubationperiod(no signs orsymptoms) Decline(declining signsand symptoms) Convalescence(no signs orsymptoms) Illness(most severe signsand symptoms) Number of microorganisms orintensity of signs or symptoms Time

46. The Movement of Pathogens Out of Hosts: Portals of Exit Pathogens leave host through portals of exit Many portals of exit are the same as portals of entry Pathogens often leave hosts in materials the body secretes or excretes © 2012 Pearson Education Inc.

47. Eyes(tears) Ear (earwax) Nose (secretions) Figure 14.11 Portals of exit Broken skin(blood) Mouth(saliva, sputum) Skin(flakes) In females:Mammary glands(milk, secretions) Vagina(secretions, blood) Anus(feces) Seminal vesicles(semen and lubricating secretions) Urethra(urine)

48. Modes of Infectious Disease Transmission Transmission is from a reservoir or a portal of exit to another host’s portal of entry Three groups of transmission Contact transmission Direct, indirect, or droplet Vehicle transmission Airborne, waterborne, or foodborne Vector transmission Biological or mechanical © 2012 Pearson Education Inc.

49. Modes of Infectious Disease Transmission ANIMATION Epidemiology: Transmission of Disease © 2012 Pearson Education Inc.

50. Figure 14.12 Droplet transmission