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Chapter 14
Principles of
Disease and
Epidemiology
Biology 205
Chandler-Gilbert Community College
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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
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 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 is a competition between
microbes.
 Normal microbiota protect the host by:
 Occupying niches that pathogens might occupy
 Producing acids
 Producing bacteriocins
 Probiotics are live microbes applied to or ingested into
the body, intended to exert a beneficial effect.
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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)
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.
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Occurrence of Disease
 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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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
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.
 Focal infection: Systemic
infection that began as a
local infection.
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Extent of Host Involvement
 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 (i.e., Sinus infection).
 Secondary infection: Opportunistic infection after a
primary (predisposing) infection (i.e., Meningitis).
 Subclinical disease: No noticeable signs or symptoms
(inapparent 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
 Vehicle: Transmission by an
inanimate reservoir
(food, water).
 Vectors: Arthropods, especially
fleas, ticks, and mosquitoes.
 Mechanical: Arthropod carries
pathogen on feet (fly).
 Biological: Pathogen
reproduces in vector (Malaria).
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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 (moisture)
 Hantavirus
 Modern Transportation (Hitching a ride)
 West Nile virus
 Ecological disaster, war, and expanding human settlement
 Coccidioidomycosis
 Animal control measures (Deer)
 Lyme disease
 Public Health failure (Lack of water treatment)
 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
Showed that improved
sanitation decreased the
incidence of epidemic typhus
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Descriptive
Collection and analysis of data Snow
regarding occurrence of disease
Analytical
Comparison of a diseased group Nightingale
and a healthy group
Experimental
Study of a disease using
controlled experiments
Case reporting
Health care workers report
specified disease to local, state,
and national offices
Nationally notifiable Physicians are required to
diseases
report occurrence
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Semmelweis
“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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Exam Review
 Read Chapter 14
 Complete the Chapter 14 Quiz
 Study the Chapter 14 Exam Notes
 Review the following YouTube video on Malaria
for a possible essay question on the Exam.
Malaria
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