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© 2012 Pearson Education Inc. Lecture prepared by Mindy Miller-Kittrell North Carolina State University Chapter 14 Infection, Infectious Diseases, and.

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Presentation on theme: "© 2012 Pearson Education Inc. Lecture prepared by Mindy Miller-Kittrell North Carolina State University Chapter 14 Infection, Infectious Diseases, and."— Presentation transcript:

1 © 2012 Pearson Education Inc. Lecture prepared by Mindy Miller-Kittrell North Carolina State University 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, pathogen © 2012 Pearson Education Inc.

3 Table 14.1 The Three Types of Symbiotic Relationships

4 Figure 14.1 Which type of symbiotic relationship?

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 (ex. E. coli) –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 –P. 416 A deadly carrier © 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 Figure 14.3 Routes of entry for invading pathogens Broken skin Insect bite Anus Ear Conjunctiva of eye Nose Mouth Placenta Vagina 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 Figure 14.4 A cross-section of skin Sebaceous (oil) gland Pore of sweat duct Epidermis Dermis Sweat gland Hair Blood capillaries Nerve fiber Nerve ending Vein Artery Fat cells Hair follicle

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 Figure 14.7 Koch ’ s postulates The suspected agent must be present in every case of the disease. Diseased subjects Agent not typically found in healthy subjects Healthy subjects Petri plate Bacterial colonies The agent must be isolated and grown in pure culture. Streaked plates Injection The cultured agent must cause the disease when it is inoculated into a healthy, susceptible experimental host (animal or plant). The same agent must be reisolated from the diseased experimental host.

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 Figure 14.8 Relative virulence of some microbial pathogens Lactobacilli, diphtheroids Candida albicans (vaginitis, thrush) Clostridium difficile (antibiotic-induced colitis) Pseudomonas aeruginosa (infections of burns) Bordetella pertussis (whooping cough) Yersinia pestis (plague) Francisella tularensis (rabbit fever) More virulent 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 Bacterium Epithelial cells Collagen layer Invasive bacteria reach epithelial surface. Hyaluronidase and collagenase Coagulase and kinase Extracellular enzymes Hyaluronidase Collagenase Bacteria produce hyaluronidase and collagenase. Bacteria invade deeper tissues. Bacterium Coagulase Clotting protein Clot Kinase Bacteria produce coagulase. Clot forms.Bacteria later produce kinase, dissolving clot and releasing bacteria.

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 Bacterium Exotoxin Toxins Endotoxin Exotoxin Bacteria secrete exotoxins, in this case a cytotoxin. Cytotoxin kills host’s cells. Phagocyte Phagocytized Gram  bacteria Exocytosis Endotoxin Dead Gram  bacteria Blood vessel Dead Gram-negative bacteria release endotoxin (lipid A), which induces effects such as fever, inflammation, diaarrhea, shock, and blood coagulation.

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

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

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 Capsule around bacterium Phagocytosis blocked by capsule Antiphagocytic factors Incomplete phagocytosis Phagocyte Capsule around bacterium Bacteria reproduce Phagocytic vesicle Lysosome

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

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 The stages of infectious diseases Incubation period (no signs or symptoms) Prodromal period (vague, general symptoms) Illness (most severe signs and symptoms) Decline (declining signs and symptoms) Convalescence (no signs or symptoms) Time Number of microorganisms or intensity of signs or symptoms

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

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

50 Figure Droplet transmission

51 Figure Poorly refrigerated foods can harbor pathogens and transmit diseases

52 Classification of Infectious Diseases Diseases can be classified in number of ways –The body system they affect –Their longevity and severity –How they are spread to their host –The effects they have on populations (rather than on individuals) © 2012 Pearson Education Inc.

53 Classification of Infectious Diseases Terms used to classify infectious disease –Acute disease –Chronic disease –Subacute disease –Latent disease –Communicable –Contagious © 2012 Pearson Education Inc.

54 Epidemiology of Infectious Diseases © 2012 Pearson Education Inc. ANIMATION Epidemiology: Overview

55 Epidemiology of Infectious Diseases Frequency of Disease –Track occurrence of diseases using two measures –Incidence –Number of new cases of a disease in a given area during a given period of time –Prevalence –Number of total cases of a disease in a given area during a given period of time –Occurrence also evaluated in terms of frequency and geographic distribution © 2012 Pearson Education Inc.

56 Figure Curves representing the incidence and the estimated prevalence of AIDS among U.S. adults Year Incidence Prevalence Incidence (thousands) Prevalence (thousands)

57 Figure Incidence of shigellosis in the U.S. in 2000-overview

58 Figure Illustrations of the different terms for the occurrence of disease-overview

59 Epidemiology of Infectious Diseases © 2012 Pearson Education Inc. ANIMATION Epidemiology: Occurrence of Disease

60 Figure Epidemics may have fewer cases than nonepidemics Expected number of cases Time Actual number of cases Disease A Actual number of cases Disease B Epidemic 1 Epidemic 2 Number of cases per 100,000 individuals

61 Figure A page from the CDC ’ s Morbidity and Mortality Weekly Report (MMWR)

62 Epidemiology of Infectious Diseases Epidemiological Studies –Descriptive epidemiology –Careful tabulation of data concerning a disease –Record location and time of the cases of disease –Collect patient information –Try to identify the index case (or first case) of the disease © 2012 Pearson Education Inc.

63 Figure A map showing cholera deaths in a section of London, 1854 Deaths from cholera Pump Oxford Street Broad Street Regent Street Marylebone Street Piccadilly

64 Epidemiology of Infectious Diseases Epidemiological Studies –Analytical epidemiology –Seeks to determine the probable cause, mode of transmission, and methods of prevention –Useful in situations when Koch’s postulates can’t be applied –Often retrospective –Investigation occurs after an outbreak has occurred © 2012 Pearson Education Inc.

65 Epidemiology of Infectious Diseases Epidemiological Studies –Experimental epidemiology –Involves testing a hypothesis concerning the cause of a disease –Application of Koch’s postulates is experimental epidemiology © 2012 Pearson Education Inc.

66 Epidemiology of Infectious Diseases © 2012 Pearson Education Inc. ANIMATION Nosocomial Infections: Overview

67 Epidemiology of Infectious Diseases Hospital Epidemiology: Nosocomial Infections –Types of nosocomial infections –Exogenous –Pathogen acquired from the health care environment –Endogenous –Pathogen arises from normal microbiota due to factors within the health care setting –Iatrogenic –Results from modern medical procedures © 2012 Pearson Education Inc.

68 Figure The interplay of factors that result in nosocomial infections Presence of microorganisms in hospital environment Immunocompromised patients Transmission of pathogens between staff and patients and among patients Nosocomial infection

69 Epidemiology of Infectious Diseases Hospital Epidemiology: Nosocomial Infections –Control of nosocomial infections –Precautions designed to reduce factors that result in disease –Hand washing is the most effective way to reduce nosocomial infections © 2012 Pearson Education Inc.

70 Epidemiology of Infectious Diseases © 2012 Pearson Education Inc. ANIMATION Nosocomial Infections: Prevention

71 Epidemiology of Infectious Diseases Epidemiology and Public Health –Local, state, national, and global agencies share information concerning disease –The United States Public Health Service –World Health Organization (WHO) –Public health agencies work to limit disease transmission –Monitor water and food safety –Public health agencies campaign to educate the public on healthful choices to limit disease © 2012 Pearson Education Inc.


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