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© 2010 Jones and Bartlett Publishers, LLC
Chapter 3
Practical Disease Concepts in
Epidemiology
© 2010 Jones and Bartlett Publishers, LLC
 World Clock
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Objective: Define disease
 Disease is an interruption, cessation, or
disorder of body functions, systems, or
organs
 Diseases arise from infectious agents,
inherent weaknesses, lifestyle, or
environmental stresses

Environment – all that is external to the
human host (physical, biological, social,
cultural, etc.)
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Causes of disease
 Identifying the causes of disease and the
mechanisms by which they spread
remains a primary focus in epidemiology
 The science and study of the causes of
disease and their mode of operation is
referred to as etiology
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Objective: Classify acute and chronic
diseases according to infectivity and
communicability
 When an infectious disease is
contagious, or capable of being
communicated or transmitted, it is called
a communicable disease
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HIV/AIDS
Cholera
Influenza
Cryptosporidiosis
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Objective: Identify various classifications of
disease and their sources and modes of
transmission
 Two types of transmission
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Vertical transmission refers to transmission
from an individual to its offspring through
sperm, placenta, milk, or vaginal
Horizontal transmission refers to
transmission of infectious agents from an
infected individual to a susceptible
contemporary
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Pathogens
 Organisms or substances such as bacteria,
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viruses, fungi, or parasites that are capable of
producing diseases
The ability to get into a susceptible host and
cause disease is termed invasiveness
The disease-evoking power of a pathogen is
called virulence
Toxins – kill pathogens by poisoning them.
Antibiotics work against pathogens because of
their toxicity
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Classifications of diseases
1. Acute – disorder with sudden onset,
relatively severe, and short duration of
symptoms
2. Chronic – less severe but of long and
continuous duration, lasting over long
time periods if not a lifetime
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Questions
 Are all infectious diseases
communicable?
 What is an example of a chronic
communicable disease?
 What is an infectious disease that is
chronic?
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Examples of diseases according to selected classifications
Communicable
Acute
Infectious
Noninfectious
Influenza/
pneumonia
Lyme disease
Mumps
Measles
Cholera
Chronic
Cancer
Leprosy
Polio
Syphilis
Tuberculosis
Non-communicable
Acute
Chronic
Tetanus
Legionnaire
s
Anthrax
Accidents
Drug abuse
Homicide
Stroke
Suicide
Alcoholism
Cancer
Diabetes
mellitus
Heart
diseases
Paralysis
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Objective: Understand the major stages in
the disease process
Stages relevant to most health-related
states or events
1. Stage of susceptibility
2. Stage of pre-symptomatic disease
•
•
Incubation period
Latency period
3. Stage of clinical disease
4. Stage of recovery, disability, or death
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Natural course of communicable disease
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Guinea Worm
 Guinea Worm (Dracunculiasis)
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Centers for Disease Control
and Prevention, “Locally
acquired neurocysticercosis—
North Carolina,
Massachusetts, and South
Carolina, 1989–1991.”
Morbidity and
Mortality Weekly Report, Public
Health Services, U.S.
Department of Health and
Human Services, Vol. 21, No.
1, Jan. 10, 1992, pp. 1–4.
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Breaking the cycle
 Viability – the capacity of the pathogen
or disease-causing agent to survive
outside the host and to exist or thrive in
the environment.
 Viability – guinea worm is 1 year.
 Solution: Break the cycle for 1 year.
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Objective 5. Know the five major categories
of disease
 Congenital and hereditary diseases
Familial tendencies toward certain inborn abnormalities
 Injury to the embryo or fetus by environmental factors
 Examples – Down syndrome, hemophilia, heart disease at an early age
Allergies and inflammatory diseases
 Body reacting to an invasion of or injury by a foreign object or substance
Degenerative diseases
 Deterioration of body systems, tissue, and functions
Metabolic diseases
 Cause the dysfunction, poor function, or malfunction of certain organs or
physiological processes within the body leading to disease states.
 Example – cells may no longer utilize glucose normally causing diabetes
Cancer
 Characterized by abnormal growth of cells that form a variety of tumors,
both benign and malignant
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Common modes of entry into the
body of infectious disease agents
1. Respiratory
2. Oral
3. Reproductive
4. Intravenous
5. Urinary
6. Skin
7. Gastrointestinal
8. Conjunctival
9. Transplacental
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Objective: Identify the role of zoonoses in
communicable disease in humans
 Animals can be the host, vector, or source of certain
infections and diseases.
 A zoonosis (plural zoonoses) is an infectious organism in
vertebrate animals (e.g., rabies or anthrax) that can be
transmitted to humans through direct contact, a fomite, or
vector.
 The word comes from the Greek words
zoon (animal) and nosos (ill).
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Common zoonotic diseases
AIDS
Amebiasis
Anthrax
Bovine papular
stomatitis
Brucellosis
California
encephalitis
Cat-scratch
fever
Colorado tick
fever
Cowpox
Dengue fever
Dermatophilosis
Leprosy
Lyme disease
Pasteurellosis
Plague
Q-fever
Rabies
Rat-bite fever
Rickettsialpox
Rocky mountain
spotted fever
Salmonellosis
Shigellosis
Streptococcus
infections
Tetanus
Trichinosis
Tularemia
Yellow fever
Zoonotic scabies
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Objective: Discuss notifiable disease
reporting in the United States
 Notifiable diseases are those of
considerable public health importance
because of their seriousness. Such
diseases
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Cause serious morbidity or death
Have the potential to spread
Can be controlled with appropriate
intervention
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Objective: Immunity and immunizations
against infectious diseases
 According to the Centers for Disease
Control and Prevention, if fewer than
80% of the children in a given area have
been inoculated for one of the
contagious diseases, the danger of
serious outbreaks or localized epidemics
remains; every unvaccinated child is at
risk
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Active and passive immunity
 Active immunity - the body produces its
own antibodies. This can occur through
a vaccine or in response to having a
specific disease pathogen invade the
body
 Passive immunity is acquired through
transplacental transfer of a mother’s
immunity from diseases to the unborn
child
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Diseases for which vaccines are used
Anthrax
Cervical Cancer (HPV)
Cholera
Chickenpox
Diphtheria
German measles (rubella)
Haemophilus influenzae type b
(Hib)
Hepatitis A
Hepatitis B
Influenza
Japanese encephalitis
Lyme disease
Measles
Meningitis
Mumps
Pertussis
Plague
Pneumonia
Polio
Rabies
Smallpox
Spotted fever
Tetanus
Tuberculosis
Typhoid fever
Typhus
Whooping cough
Yellow fever
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Smallpox
 If smallpox were introduced into our
classroom…
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Herd immunity
 Viewed as the resistance a population
has to the invasion and spread of an
infectious disease
 Based on the notion that if a population
or group is mostly protected from a
disease by immunizations (say 80% or
more) , then the chance of a major
epidemic occurring is highly limited
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Estimated Herd Immunity
thresholds for vaccine
preventable diseases
Diptheria
85%
Polio
80-86%
Measles
83-94%
Mumps
75-86%
Pertussis
92-94%
Rubella
80-85%
Smallpox
83-85%
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Objective: Identify the changing emphasis
of epidemiologic study
 Increasing life expectancy in modern
times and higher levels of chronic
disease has produced a change in the
emphasis of epidemiologic studies
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Percentage of deaths attributed to selected
infectious and chronic diseases in the United
States
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Host-related control and prevention
 Isolation applies to persons who are
known to be ill with a contagious
disease. It is often conducted on an
inpatient basis in hospitals or nursing
homes. Most state laws as well as
accrediting organizations require one or
two beds to be kept, designated, and
equipped in a hospital or nursing home
as isolation beds.
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Host-related control and prevention
Quarantine applies to persons who have been exposed to a contagious
disease but may or may not become ill. These people may not know whether
they have been exposed to a disease or they may have the disease but not
manifest clinical symptoms (e.g., Typhoid Mary). Quarantine may also refer to
situations where a building, cargo, conveyance, or animal may be believed to
be exposed to a dangerous contagious disease and is, therefore, closed or kept
apart from others in order to prevent the spread of disease. Quarantine has
been used throughout history to stop the spread of disease. Quarantine was
probably the first public health measure to show a marked level of effectiveness
in controlling the spread of disease. In the late 1800s and early 1900s,
quarantine activities became an organized effort by government officials, and
this had a major impact on improving the health status of the community,
especially with regard to mortality statistics. In modern times, quarantine
measures are still in use. Currently, the WHO invokes quarantine measures for
three diseases: cholera, plague, and yellow fever.
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Objective: Be familiar with common
nutritional deficiency diseases and
disorders
 Malnutrition - a condition that arises
when the body does not get the right
amount of vitamins, minerals, and other
nutrients to maintain healthy tissues and
proper organ function. Malnutrition occurs
in people experiencing either undernutrition or over-nutrition.
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Malnutrition syndromes
Kwashiorkor (protein deficiency)
Marasmus (protein-calorie malnutrition, chronic
undernutrition)
Iron-deficiency anemia
Folic acid-deficiency anemia
Vitamin B12-deficiency anemia
Xerophthalmia (vitamin A deficiency)
Endemic goiter (iodine deficiency)
Beriberi (thiamine deficiency)
Ariboflavinosis (riboflavin deficiency)
Pellagra (niacin and amino acid tryptophan
deficiency)
Scurvy (vitamin C deficiency)
Rickets (vitamin D deficiency)
Tetany (mineral deficiency)
Osteomalacia and osteoporosis (impaired calcium and
phosphorus metabolism affecting bone formation)
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Undernutrition
 A consequence of consuming too little essential
vitamins, minerals, and other nutrients or excreting
them faster than they can be replenished.
 Inadequate intake may result from excessive dieting,
severe injury, and serious illness.
 Excessive loss may result from diarrhea, heavy
sweating, heavy bleeding, or kidney failure.
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Overnutrition
 The consumption of too much food,
eating too many of the wrong things,
too little physical activity and
exercise, or taking too many
vitamins or dietary supplements.
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Objective: Be familiar with selected chronic
diseases and conditions
 Cardiovascular disease, cancer, chronic
obstructive pulmonary disease, diabetes
mellitus, and mental health disorders
 Chronic diseases are not typically caused by an
infectious agent (pathogen), but result from
genetic susceptibility, lifestyle, or environmental
exposures
 Some exceptions are cancers of the cervix, liver,
and stomach
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Characteristics of chronic
diseases
 The latency period for chronic diseases is
typically more difficult to identify than is the
incubation period for acute infectious diseases
 This explained by the multifactorial etiology
which characterizes many chronic diseases
 Multifactorial Nature of Chronic Disease
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Disability
 Umbrella term for impairments, activity
limitations, and participation restriction
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Impairments - any loss or abnormality of
psychological, physiologic, or anatomic
structure or function
Activity limitations are difficulties an
individual may have in executing activities
Participation restrictions are problems
an individual may experience in
involvement in life situations
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