Download Chapter 14: Principles of Epidemiology

BIOLOGY 221: Lecture Test #3 Study Guide
Chapter 14: Principles of Epidemiology
I.
Pathology, Infection and Disease
A. Pathology - study of disease
B. Etiology - study of the cause of a disease
C. Infection - colonization of the body by pathogens
D. Epidemiology - study of where diseases occur and how they are transmitted in
populations
E. Pathogenisis - the manner in which a disease develops
II.
Symbiosis
A. Mutualism - both organisms benefit from the relationship
B. Commensulism - one organism benefits and the other is unaffected
C. Parisitism - one organism benefits at the expense of the other
D. Saphrophy - an organism that feeds on dead organic matter (technically not a
form of symbiosis because symbiosis is between two LIVING organisms)
IV. Koch's Postulates
A. The same pathogen must be present in every case of the disease
B. The pathogen must be isolated from the diseased host and grown in pure
culture
C. The pathogen from the pure culture must cause the disease when it is
inoculated into a healthy; susceptible laboratory animal
D. The pathogen must be isolated from the inoculated animal and must be shown
to be the original organism
E. Exceptions
i.
Microorganisms that cannot be grown on artificial media
ii. When one disease can be caused by several pathogens
iii. When one pathogen can cause several diseases
iv. Ethical considerations sometimes prevent experimentation with human
hosts
V.
Classifying Infectious Diseases
A. Symptom - change in body function that is felt by a patient as a result of a
disease (cannot be measured or observed)
B. Sign - change in body that can be measured or observed as a result of the
disease
C. Syndrome - a specific group of signs and symptoms that accompany a disease
D. Communicable disease - a disease that can spread from one host to another
i.
Contagious diseases - a disease that is easily spread from one host to
another
E. Noncommunicable disease - a disease that is not transmitted from one host to
another
VI. Occurrence of a Disease
A. Incidence - The fraction of a population that contracts a disease during a
specific time (how many new cases in a time period)
B.
C.
D.
E.
F.
Prevalence - The fraction of a population having a specific disease at a given
time (how wide spread)
Endemic disease - a disease that is constantly present in a population
Epidemic disease - a disease acquired by many hosts in a given area in a short
time
Pandemic disease - a worldwide epidemic
Herd immunity - when a high enough percentage of a population is immune to
the disease so much that the disease cannot easily spread
VII. Severity or Duration of a Disease
A. Acute disease - disease develops rapidly but lasts only a short time
B. Chronic disease - disease develops more slowly and usually is continual or
recurrent for a longer periods of time
VIII. Stages of a Disease
IX. Extent of Host Involvement
A. Local infection - pathogens limited to a small area of the body
B. Systemic infection - an infection throughout the body
C. Focal infection - systemic infection that began as a local infection
D. Bacteremia - the presence bacteria in the blood
E. Septicemia - growth of bacteria in the blood
F. Toxemia - toxins in the blood
G. Viremia - viruses in the blood
H. Primary infection - acute infection that causes the initial illness
J.
Secondary infection - infection caused by an opportunistic pathogen after the
primary infection has weakened the body's defenses
X.
Transmission of Disease
A. Contact transmission - spread of an agent of disease by direct contact, indirect
contact, or droplet transmission
i.
Direct contact transmission - require close association between infected
and susceptible host
ii. Indirect contact transmission - spread by fomites (non-living object
involved in the spread of an infection)
iii. Droplet transmission - transmission via airborne droplets
B. Vehicle transmission - transmission by an inanimate reservoir (food, water,
air, blood, etc)
C.
Vectors - arthropods especially fleas, ticks, and mosquitoes that carry
pathogens from one host to another via mechanical transmission or biological
transmission
Chapter 15: Microbial Mechanisms of Pathogenicity
I.
Pathogenicity & Virulence
A. Pathogenicity - the ability to cause disease
B. Virulence - the extent of pathogenicity
II.
Portals of Entry
A. Mucous membranes
i.
Respitory tract
a.
The easiest and most frequently traveled portal of entry for infectious
microorganisms
ii. Gastrointestinal tract
iii. Genitourinary tract
B. Skin (unbroken)
C. Parenteral route
i.
Microorganisms deposited directly into the tissues beneath the skin or mucous
membranes when these barriers are penetrated or injured
III.
Numbers of Invading Microbes
A. ID50 - The infectious dose for 50% of the population
B. LD50 - The lethal dose (of a toxin) for 50% of the population
IV. Pathogen Adherence
A. Refers to the pathogen's ability to attach itself to host tissue
V.
Penetration
A. Pathogens can penetrate host defenses by
i.
Capsules - resist phagocytosis
ii. Cell wall components - may resist heats or acids; may resist phagocytosis; may enhance
attachment to host cells
iii. Enzymes - may clot blood; may break down connective tissue; may destroy antibodies
iv. Antigenic variation - alterations of surface antigens to avoid host detection and immune
response
v.
Penetration of host cell cytoskeleton - use the host cytoskeleton to move around inside
the wall
VI. Damage
A. Pathogens can damage host cells by
i.
Siderophores - bacterial proteins that "steal" iron from the host cell
ii. Direct damage - may use nutrients of host cell; may produce waste products; may
rupture the host cell
iii. Toxins
a.
Exotoxins - come mostly from living gram-positive bacteria; secreted as specific
weapons or metabolic by products
Type 1 - superantigens or antigens that provoke a very intense
immune response
-
b.
Type 2 - membrane-disrupting toxins that cause lysis of host cells
by disrupting their plasma membranes
Type 3 - A-B toxins have two components which are the active (enzyme)
component and the binding component.
Endotoxins - come from the cell wall of dead or dividing gram-negative bacteria;
structural component of the cell's outer membrane
VII. Antogen vs. Antitoxin
A. Antogen - any substance that causes antibody formation and reacts only with its specific
antibody
B. Antitoxin - a specific antibody produced by the body in response to a toxin
VIII. LAL (Limulus Ameobocyte Lysate) test
A. Can detect even minute amounts of endotoxin