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TORTORA  FUNKE  CASE
ninth edition
MICROBIOLOGY
an introduction
14
Principles of
Disease and
Epidemiology
PowerPoint® Lecture Slide Presentation prepared by Christine L. Case
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Principles of Disease and Epidemiology
 Pathology: The study of disease
 Etiology: The study of the cause of a disease
 Pathogenesis: The development of disease
 Infection: Colonization of the body by pathogens
 Disease: An abnormal state in which the body is not
functioning normally
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Normal Microbiota and the Host
 Transient microbiota may be
present for days, weeks, or
months.
 Normal microbiota permanently
colonize the host.
 Symbiosis is the relationship
between normal microbiota and
the host.
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Figure 14.1c
Normal Microbiota and the Host
 Not all microorganisms are pathogenic – most can
actually help the body
 E. coli is typically found in the intestines of healthy
adults, however, if it is found in other parts of the body
it can lead to disease.
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Symbiosis
 In commensalism, one organism is benefited and the
other is unaffected.
 In mutualism, both organisms benefit.
 In parasitism, one organism is benefited at the expense
of the other.
 Some normal microbiota are opportunistic pathogens.
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Normal Flora
 After birth, during eating / breathing other microbiota
become permanent on the body….
 The one’s that do become permanent on the body
become the “normal flora”
 Transient microbiota are those that are present on the
body for days / weeks / months but are not permanent
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Normal Flora
 Factors that determine presence of microbiota
 Available nutrients, physical / chemical factors,
defenses of the host
 Age, diet, health, nutritional status, climate, hygene,
lifestyle, occupation
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Normal Microbiota and the Host
 Locations of normal
microbiota on and in
the human body.
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Table 14.1c
Normal Microbiota and the Host
 Microbial antagonism (competitive exclusion) is a
competition between microbes.
 Normal microbiota protect the host by:
 Occupying niches that pathogens might occupy.
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 Commensalism (most of our normal flora) is when 1
organism benefits from a relationship and the other is
neither hurt nor helped
 Mutualism leads to benefits for both organisms
 Parasitism is where one organism is benefited and the
other is harmed – can often lead to disease
 Opportunistic microorganisms do not typically cause
disease, however, if the host is in some way
compromised, it will colonize / cause disease
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Robert Koch
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Koch’s Postulates
 Koch's postulates are
used to prove the
cause of an infectious
disease.
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Figure 14.3 (1 of 2)
Koch’s Postulates
 Koch's postulates are
used to prove the
cause of an infectious
disease.
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Figure 14.3 (2 of 2)
Koch’ Postulates
1. The same pathogen must be present in every case of
the disease.
2. The pathogen must be isolated from the diseased host
and grown in pure culture.
3. The pathogen must cause the disease when
innoculated into a healthy host.
4. The pathogen must be isolated from the innoculated
organism and must be the original microorganism
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Classifying Infectious Diseases
 Symptom: A change in body function that is felt by a
patient as a result of disease.
 Sign: A change in a body that can be measured or
observed as a result of disease.
 Syndrome: A specific group of signs and symptoms
that accompany a disease.
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Classifying Infectious Diseases
 Communicable disease: A disease that is spread from
one host to another.
 Contagious disease: A disease that is easily spread
from one host to another.
 Noncommunicable disease: A disease that is not
transmitted from one host to another.
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Occurrence of Disease
 Incidence: Fraction of a population that contracts a disease
during a specific time.
 Prevalence: Fraction of a population having a specific disease at
a given time.
 Sporadic disease: Disease that occurs occasionally in a
population.
 Endemic disease: Disease constantly present in a population.
 Epidemic disease: Disease acquired by many hosts in a given
area in a short time.
 Pandemic disease: Worldwide epidemic.
 Herd immunity: Immunity in most of a population.
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Figure 14.4
Severity or Duration of a Disease
 Acute disease: Symptoms develop rapidly.
 Chronic disease: Disease develops slowly.
 Subacute disease: Symptoms between acute and
chronic.
 Latent disease: Disease with a period of no symptoms
when the patient is inactive.
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Extent of Host Involvement
 Local infection: Pathogens are limited to a small area
of the body.
 Systemic infection: An infection throughout the body.
 Bacteremia: Bacteria in the blood.
 Septicemia: Growth of bacteria in the blood.
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Extent of Host Involvement
 Toxemia: Toxins in the blood.
 Viremia: Viruses in the blood.
 Primary infection: Acute infection that causes the
initial illness.
 Secondary infection: Opportunistic infection after a
primary (predisposing) infection.
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Predisposing Factors
 Make the body more susceptible to disease
 Short urethra in females
 Inherited traits such as the sickle-cell gene
 Climate and weather
 Fatigue
 Age
 Lifestyle
 Chemotherapy
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The Stages of a Disease
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Figure 14.5
Reservoirs of Infection
 Reservoirs of infection are continual sources
of infection.
 Human — AIDS, gonorrhea
 Carriers may have inapparent infections
or latent diseases.
 Animal — Rabies, Lyme disease
 Some zoonoses may be transmitted to humans.
 Nonliving — Botulism, tetanus
 Soil
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Transmission of Disease
 Contact
 Direct: Requires close association between infected
and susceptible host.
 Indirect: Spread by fomites.
 Droplet: Transmission via airborne droplets.
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Transmission of Disease
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Figure 14.6a, d
Transmission of Disease
 Vehicle: Transmission by an inanimate reservoir
(food, water).
 Vectors: Arthropods, especially fleas, ticks, and
mosquitoes.
 Mechanical: Arthropod carries pathogen on feet.
 Biological: Pathogen reproduces in vector.
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Transmission of Disease
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Figures 14.7b, 14.8
Nosocomial (Hospital-Acquired) Infections
 Are acquired as a result of a hospital stay.
 5-15% of all hospital patients acquire nosocomial
infections.
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Figures 14.6b, 14.9
Relative Frequency of Nosocomial Infections
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Table 14.5
Common Causes of Nosocomial Infections
Percentage of
Nosocomial
Infections
Percentage
Resistant to
Antibiotics
Gram + cocci
51%
29%-89%
Gram – rods
30%
3-32%
Clostridium difficile
13%
Fungi
6%
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Emerging Infectious Diseases
 Diseases that are new, increasing in incidence, or
showing a potential to increase in the near future.
 Contributing factors
 Genetic recombination
 E. coli 0157, Avian influenza (H5N1)
 Evolution of new strains
 V. cholerae 0139
 Inapproriate use of antibiotics and pesticides
 Antibiotic resistant strains
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Emerging Infectious Diseases
 Changes in weather patterns
 Hantavirus
 Modern Transportation
 West Nile virus
 Ecological disaster, war, and expanding human settlement
 Coccidioidomycosis
 Animal control measures
 Lyme disease
 Public Health failure
 Diphtheria
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Crossing the Species Barrier
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UN 13.3
Epidemiology
 The study of where
and when diseases
occur
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Figure 14.10
Epidemiology
John Snow
1848-1849
Mapped the occurrence of
cholera in London
Ignaz Semmelweis
1846-1848
Showed that hand washing
decreased the incidence of
puerperal fever
Florence Nightingale 1858
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Showed that improved
sanitation decreased the
incidence of epidemic
typhus
Descriptive
Collection and analysis of data Snow
regarding occurrence of
disease
Analytical
Comparison of a diseased
group and a healthy group
Nightingale
Experimental
Study of a disease using
controlled experiments
Semmelweis
Case reporting
Health care workers report
specified disease to local,
state, and national offices
Nationally notifiable
diseases
Physicians are required to
report occurrence
PLAY
Animation: Epidemiology
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“AIDS” to “Gonorrhea”; “Pertussis” to
“Streptococcal Toxic Shock Syndrome”
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Table 14.7 (1 of 2)
“Haemophilus influenzae” to “Mumps”;
“Streptococcus pneumonaie” to “Yellow Fever”
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Table 14.7 (2 of 2)
Centers for Disease Control
and Prevention (CDC)
 Morbidity: Incidence of a specific notifiable disease.
 Mortality: Deaths from notifiable diseases.
 Morbidity rate: Number of people affected in relation to
the total population in a given time period.
 Mortality rate: Number of deaths from a disease in
relation to the population in a given time.
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Centers for Disease Control
and Prevention (CDC)
 Collects and analyzes epidemiological information in
the United States.
 Publishes Morbidity and Mortality Weekly Report
(MMWR) www.cdc.gov
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