VBS 2032 - Exam 3 Study Questions
Principles of Epidemiology
Learning Objectives:
· Understand terminology used in infectious disease and epidemiology
· Name the three points of the “Epidemiological Triad” and describe how factors from each point influence disease transmission...
VBS 2032 - Exam 3 Study Questions
Principles of Epidemiology
Learning Objectives:
· Understand terminology used in infectious disease and epidemiology
· Name the three points of the “Epidemiological Triad” and describe how factors from
each point influence disease transmission in populations.
· Describe the steps in the traditional Koch’s Postulates and explain why each is necessary.
· Explain how Molecular Koch’s Postulates have been used to study virulence factors
of Yersinia pestis.
Study Questions:
(1) Be able to explain all terminology in red.
(2) What types of virulence factors help a pathogen spread through the body, evade the
host immune defenses or cause damage to the host?
(3) If you stay home during the symptomatic phase of illness, will you avoid infecting
other people?
no, oftentimes people are contagious before the symptoms appear
(4) What is the difference between an asymptomatic carrier and a person with a latent infection?
Asymptomatic people are still contagious, there body is just able to suppress
the systems due to their specific immune response
Latent infections are not contagious, virus is not actively replicating (Herpes simplex)
(5) What is a fomite?
Inanimate objects that can transmit pathogens (utensils, phones, etc)
(6) What types of microorganisms are transmitted directly?
,Direct transmission: of a pathogen from one host to another involves immediate
transfer of the infectious agent to portal of entry. Occurs via direct physical contact or
projection of respiratory droplets onto mucous membranes.
(7) What is the difference between a microbial intoxication and a microbial infection?
- Microbial intoxication - the toxin is ingested
Main question that determines this: how long did it take for you to get sick?
- Microbial infection - the toxin multiplies within the body
(8) What are some examples of when Koch’s postulates could not be satisfied?
- 1. Suspected germ must be present in every case
-Examine samples from diseased subjects via bacterial colonies
present -Essential for next step
- 2. Germ must be isolated and grown in pure culture
-Useful to have to inoculate experimental host
- 3. Cultured germ must cause disease when in healthy, experimental host
- 4. Same germ must be reisolated from diseased experimental host
-Important bc that means the germ is the same cause of disease from
first infected organisms
- 1) Pathogen cannot be isolated and grown in pure culture (obligate intracellular
organism, something w/v specific growth requirements that are unknown)
- 2) Presence of biofilm - more than one organism present that causes disease
- 3) Asymptomatic carriers - cannot characterize people who get sick vs.
those who do not
- 4) No animal model to perform tests
(9) How did Zimbler et al. determine that a mutated form of pla increased the virulence of
Y. pestis?
, Koch's postulates
There is a virulence gene in pla of the ancestral strain which has become mutated in
the modern form
- Mutated play causes disseminated infection
Pla was not found in the ancient bacteria, but was found in more modern bacteria.
The modern bacteria had a single nucleotide difference which caused this pla gene
(10) What virulence factor allows the pathogen to live inside of fleas? How does this
influence the transmission of the bacterium?
(11) What is the difference between direct and indirect transmission? What are some examples
of each?
Direct:
< 1 meter
Sneeze/cough
Droplet spread (inhalation of respiratory droplets) - large drops- drop less than
1m Handshake
Sexual contact
Indirect:
Airborne (particles larger than 10 um are inhaled)
Fomites: inanimate object that can harbor pathogen (book, clothing,
towels) Food/water
Vectors (any living organism that can carry a disease causing microbe) ie mosquitos
(12) What is the difference between a biological and a mechanical vector?
Mechanical
Moves microbe from one place to another (carrier)
- ie Fly goes on agar, and then touches food and you eat
it House fly, cockroach
Biological
Participates in the life cycle of the pathogen and provides place for it to
multiply - ie Mosquitoes carry the malaria pathogen
(13) What is herd immunity and how does it protect unvaccinated members of the population?
Herd immunity occurs when the majority of a population/group is immune to a
disease/sickness via immunization. The principle demonstrates that as long as most
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