Chapter 14
Principles of Disease and Epidemiology
1.
What is disease, pathology, pathogenesis, a pathogen, infection, the forms of
symbiosis, normal flora, and an opportunist?
Principles of Disease and Epidemiology
Pathology Study
of disease
Etiology Study
of the cause of a disease
Pathogenesis Development of disease
Infection Colonization
of the body by pathogens
Disease An
abnormal state in which the body
is not functionally normally
2. Why is each member of the disease
triangle important for the existence of a disease?
Agent (cause of disorder)
Reservoir (between susceptible hosts)
Susceptible Host
6. What is meant by portals of entrance
and exit?
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
Normal Microbiota and the Host:
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.
Normal Microbiota and the Host:
Locations
of normal microbiota on and in the human body
Normal Microbiota and the Host:
Microbial
antagonism is 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.
Review of Kochs Postulates
Koch's
Postulates are used to prove the cause of an infectious disease.
Kochs Postulates
Koch's
Postulates are used to prove the cause of an infectious disease.
5. Understand the
terminology involved in the classification of disease.
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.
Classifying Infectious Diseases
Communicable
disease A disease that is easily 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.
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.
10. What is an epidemic?
Severity or Duration of a Disease
9. Why are health and disease a
dynamic relationship?
Subclinical
disease Disease without identifiable
signs (dont know youre sick)
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
Extent of Host Involvement
Local
infection Pathogens 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
Bacteremia Bacteria
in the blood
Septicemia Growth
of bacteria in the blood
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
Subclinical
disease No noticeable signs or
symptoms (inapparent
infection)
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
The Stages of a Disease
Reservoirs of Infection
3. What are the 3 resevoirs an agent could use?
4. What is a zoonosis?
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,
inanimate objects (fomites) food and water
Transmission of Disease
7. Explain the 3
modes of transmission and 2 examples of diseases that are propagated by each
mode. (CD Definitions)
1. Direct Transmission
Direct contact: Requires close association between
infected and susceptible host (touch, bite, sex, kiss, etc.)
Droplet spread via airborne droplets (<1m)
Transmission of Disease
Transmission of Disease
2. Indirect Transmission
Vehicle-borne:
Transmission by an inanimate reservoir (food, water) and fomites
Vector
borne: Arthropods, especially fleas, ticks, and mosquitoes
Mechanical vector: Arthropod carries pathogen on feet
Biological vectors: Pathogen
reproduces in vector
Transmission of Disease
8. What are the stages or events an
agent must go through before it can cause disease?
Nosocomial (Hospital-Acquired) Infections
Are
acquired as a result of a hospital stay
5-15%
of all hospital patients acquire nosocomial infections
Relative frequency of nosocomial infections
Common Causes of Nosocomial Infections
Emerging Infectious Diseases
Diseases
that are new, increasing in incidence, or showing a potential to increase in
the near future.
Contributing
factors:
Evolution
of new strains
V.
cholerae O139
Inappropriate
use of antibiotics and pesticides
Antibiotic
resistant strains
Changes
in weather patterns
Hantavirus
Emerging Infectious Diseases
Contributing
factors:
Modern
transportation
West
Nile virus
Ecological
disaster, war, expanding human settlement
Coccidioidomycosis
Animal
control measures
Lyme
disease
Public
Health failure
Diphtheria
Epidemiology
The
study of where and when diseases occur
Historic Epidemiology
Types of Epidemiology and Terminology
Descriptive vs. Analytic Epidemiology
11. What are the 2 types of studies done in
descriptive epidemiology?
Descriptive Epidemiologic Studies:
Retrospective
Study is a comparison of those already sick
Prospective
study follows population through time to determine risk factors for disease
Descriptive vs. Analytic Epidemiology
12. What are the 2 methods of study for
analytic epidemiology?
Analytic Epidemiological Studies:
Case-Control
Study is retrospective exam of two matched populations, one with and one
without disease under study.
Cohort
study is a prospective study used to analyze a suspect factor in
occurrence. Cohorts are 2 matched
groups, one exposed and one not exposed to suspect factor. Compare incidence between groups over time.
Experimental Epidemiology
13.
Describe an experimental epidemiological study.
Must
involve an experimental variable used by experimental group and not by control
groups.
Examples:
vaccine tests, use of aspirin in CVD, new antibiotics. Walter Reed and yellow fever
Rare
due to ethical considerations
Notifiable Diseases 2002
Centers for Disease Control and Prevention (CDC)
Collects
and analyzes epidemiological information in the U.S.
Publishes
Morbidity and Mortality Weekly Report (MMWR) www.cdc.gov
Morbidity: incidence of a specific notifiable disease
Mortality: deaths from notifiable diseases
Morbidity rate = number of people affected/total population in a given time
period
Mortality rate - number of deaths from a disease/total population in a
given time