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Infection, Infectious Diseases, and Epidemiology
Chapter 14 Infection, Infectious Diseases, and Epidemiology
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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 Pathogen=parasite that causes disease © 2012 Pearson Education Inc. 2
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Table 14.1 The Three Types of Symbiotic Relationships
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Figure 14.1 Which type of symbiotic relationship?
Mutualism
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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. 5
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Figure 14.2 Normal microbiota of the human nasal cavity
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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. 7
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Table 14.2 Some Resident Microbiota
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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. 9
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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. 10
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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. 11
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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. 12
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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. 13
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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. 14
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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. 15
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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. 16
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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. 17
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Figure 14.3 Routes of entry for invading pathogens
Ear Broken skin Insect bite Conjunctiva of eye Nose Mouth Placenta Vagina Anus In males: Penis Urethra
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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. 19
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Figure 14.4 A cross-section of skin
Sebaceous (oil) gland Hair Pore of sweat duct Blood capillaries Epidermis Nerve fiber Dermis Nerve ending Vein Artery Sweat gland Fat cells Hair follicle
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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. 21
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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. 22
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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. 23
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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. 24
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Figure 14.5 The adhesion of pathogens to host cells-overview
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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. 26
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Figure 14.6 Dental plaque
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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. 28
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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. 29
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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. 30
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Figure 14.7 Koch’s postulates
The suspected agent must be present in every case of the disease. Agent not typically found in healthy subjects Diseased 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.
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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. 32
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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. 33
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Figure 14.8 Relative virulence of some microbial pathogens
More virulent Francisella tularensis (rabbit fever) 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
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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. 35
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Figure 14.9a Some virulence factors: Extracellular enzymes
Hyaluronidase and collagenase Coagulase and kinase Bacterium Hyaluronidase Bacterium Coagulase Clot Clotting protein Kinase Epithelial cells Collagenase Collagen layer Invasive bacteria reach epithelial surface. Bacteria produce hyaluronidase and collagenase. Bacteria invade deeper tissues. Bacteria produce coagulase. Clot forms. Bacteria later produce kinase, dissolving clot and releasing bacteria. Extracellular enzymes
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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. 37
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Figure 14.9b Some virulence factors: Toxins
Exotoxin Endotoxin Bacterium Exotoxin Phagocyte Phagocytized Gram bacteria Exocytosis Endotoxin Dead Gram bacteria Blood vessel Bacteria secrete exotoxins, in this case a cytotoxin. Cytotoxin kills host’s cells. Dead Gram-negative bacteria release endotoxin (lipid A), which induces effects such as fever, inflammation, diaarrhea, shock, and blood coagulation. Toxins
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The Nature of Infectious Disease
ANIMATION Virulence Factors: Exotoxins © 2012 Pearson Education Inc. 39
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The Nature of Infectious Disease
ANIMATION Virulence Factors: Endotoxins © 2012 Pearson Education Inc. 40
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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. 41
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Figure 14.9c Some virulence factors: Antiphagocytic factors
Phagocytosis blocked by capsule Incomplete phagocytosis Capsule around bacterium Capsule around bacterium Bacteria reproduce Phagocytic vesicle Phagocyte Lysosome Antiphagocytic factors
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The Nature of Infectious Disease
ANIMATION Virulence Factors: Hiding from Host Defenses © 2012 Pearson Education Inc. 43
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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. 44
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Figure 14.10 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) Number of microorganisms or intensity of signs or symptoms Time
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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. 46
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Seminal vesicles (semen and lubricating secretions)
Figure Portals of exit Eyes (tears) Ear (earwax) Nose (secretions) 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)
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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. 48
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Modes of Infectious Disease Transmission
ANIMATION Epidemiology: Transmission of Disease © 2012 Pearson Education Inc. 49
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Figure 14.12 Droplet transmission
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Figure 14.13 Poorly refrigerated foods can harbor pathogens and transmit diseases
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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. 52
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Classification of Infectious Diseases
Terms used to classify infectious disease Acute disease Chronic disease Subacute disease Latent disease Communicable Contagious © 2012 Pearson Education Inc. 53
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Epidemiology of Infectious Diseases
ANIMATION Epidemiology: Overview © 2012 Pearson Education Inc. 54
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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. 55
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Prevalence (thousands)
Figure Curves representing the incidence and the estimated prevalence of AIDS among U.S. adults Incidence Prevalence Prevalence (thousands) Incidence (thousands) Year
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Figure 14.15 Incidence of shigellosis in the U.S. in 2000-overview
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Figure 14.16 Illustrations of the different terms for the occurrence of disease-overview
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Epidemiology of Infectious Diseases
ANIMATION Epidemiology: Occurrence of Disease © 2012 Pearson Education Inc. 59
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Figure 14.17 Epidemics may have fewer cases than nonepidemics
Number of cases per 100,000 individuals Epidemic 2 Epidemic 1 Time Expected number of cases Actual number of cases Disease A Actual number of cases Disease B
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Figure 14.18 A page from the CDC’s Morbidity and Mortality Weekly Report (MMWR)
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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. 62
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Figure 14.19 A map showing cholera deaths in a section of London, 1854
Oxford Street Broad Street Regent Street Marylebone Street Deaths from cholera Piccadilly Pump
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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. 64
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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. 65
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Epidemiology of Infectious Diseases
ANIMATION Nosocomial Infections: Overview © 2012 Pearson Education Inc. 66
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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. 67
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Presence of microorganisms in hospital environment
Figure The interplay of factors that result in nosocomial infections Presence of microorganisms in hospital environment Immunocompromised patients Nosocomial infection Transmission of pathogens between staff and patients and among patients
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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. 69
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Epidemiology of Infectious Diseases
ANIMATION Nosocomial Infections: Prevention © 2012 Pearson Education Inc. 70
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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. 71
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