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VBS 2032 - exam 3 Questions And Answers
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What types of virulence factors help a pathogen spread through the body, evade the host immune defenses or cause damage to the host? - ANS If you only stay home during the symptomatic phase of illness, will you avoid infecting other people? - ANS What is the difference betwe...

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  • October 24, 2024
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VBS 2032 - exam 3 Questions And
Answers


What types of virulence factors help a pathogen spread through the body, evade the host
immune defenses or cause damage to the host? - ANS

If you only stay home during the symptomatic phase of illness, will you avoid infecting other
people? - ANS

What is the difference between an asymptomatic carrier and a person with a latent infection? -
ANS -A carrier: is asymptomatic but is still shedding the pathogens, making the people
around them sick. (Eg. Typhoid Mary; a cook for wealthy families. Had Typhoid Fever, but
instead of her body ridding the salmonella typhi, the organism continued to proliferate in her
gallbladder. Poor handwashing before food preparation, got families sick. High mortality rate).
-latent infection: pathogen is not eliminated from the body, but is *not* actively replicating; may
become activated and cause disease. Infection is *not* spread. (Eg. HSV1 and HSV2, Varicella
Zoster (chickenpox), and Tb).

What is a fomite? - ANS An object that transmits diseases such as a door knob,
microphone, etc...

What types of microorganisms are transmitted directly? - ANS

What is the difference between a microbial intoxication and microbial infection? - ANS
Microbial intoxication: the toxin is ingested. (Food poisoning, Staphylococcus aureus)
Microbial infection: The bacterium multiplies in the body. (Staphylococcus aureus, skin
infection).

What are some examples of when Koch's postulates could not be satisfied? - ANS 1)
Cannot be cultured (obligate intracellular pathogens, eg. Rickettsia)
2) When there's no animal host
3) When an infection is caused by more than one organism
4) Healthy subjects can carry organisms and not be ill

How did Zimbler et al. determine that a mutated form of pla increased the virulence of Y. pestis?
- ANS 1. They took the ancestral strain, injected it into mice, and found a very limited
infection.

,2. Then, they put in the virulence gene pla in the ancestral strain and then injected the mice,
then pneumonic plague was present in mouse (easily spread).
3. Then, they took the mutated pla virulence gene and put it into the ancestral strain, injected it
into the mice, and found that disseminated infection could happen (bacteria could leave the
lungs and invade the body)
**Example of molecular Koch's postulate. Showed that evolution of Y. Pestis developed
virulence.

What virulence factor allows the pathogen to live inside of fleas? How does this influence the
transmission of the bacterium? - ANS

What is the difference between direct and indirect transmission? What are some examples of
each? - ANS Direct: (<1-meter proximity). Sneeze or cough (droplet), handshake, and
sexual contact.
Indirect: Airborne, fomites, food/water, vectors. Smaller, dryer, and longer-travelling microbes.

What is the difference between a biological and a mechanical vector? - ANS Biological: a
non-human animal. Part of the pathogen's life cycle occurs in the vector).
Mechanical: Just carriers. Houseflies, cockroaches. Fomites.

What is herd immunity and how does it protect unvaccinated members of the population? - ANS
Herd immunity is where enough people are vaccinated so that even those who aren't vaccinated
can be protected.
It protects these people by breaking the chain of transmission. The transmitting case encounters
an immune individual, and that immune individual cannot spread it to the susceptible.

Why can't some people receive vaccinations? - ANS Many reasons: compliance,
accessibility, and immune status. Immunocompromised persons cannot receive live attenuated
vaccines.

What is the difference between R0 and R? What factors influence these numbers? - ANS
*The reproduction number*
-R0: the basic reproductive number. How many cases an infected person will cause in a
susceptible population. (for SARS CoV2, it is between 1.5 and 3.5)
-R: the effective reproductive number. How many cases an infected person will cause in a
population with some immunity.
*How many people the infected person is likely to infect*
*R is not a biological constant for a pathogen*

How does the value of R0 influence vaccination strategies? - ANS Is used to calculate the
% of the population that needs to be immunized in order to achieve herd immunity (measles
R0=12-18. Herd immunity: 93-95%, Polio R0: 5-7, Herd Immunity: 80-85%, seasonal influenza
R0: 1-2).

, A disease with which of the following reservoirs would be the least difficult to eradicate using
vaccination?

A. domesticated animals
B. wild animals
C. humans only
D. environment - ANS C - Humans only

A fly transmitted fecal coliforms to an uncovered dish at a picnic. This is an example of what
type of transmission:

A. Direct
B. Airborne
C. Biological vector
D. Mechanical vector - ANS D - Mechanical Vector

Steps in the pathogenesis of infectious disease: - ANS 1. Entry
2. Attachment
3. Multiplication
4. Invasion or spread (in some cases)
5. Evasion of host defenses
6. Damage to host tissue(s)

4 phases of infectious disease:
At what stage are you infectious? - ANS 1) the incubation period (length is specific to each
organism)
2) The prodromal period. (Not seen in all infectious diseases. You feel off/tired but do not have
the clinical signs of disease)
3) Period of illness (symptomatic)
4) The convalescent period (the movement back toward the non disease state)(Disability or
death).
--You can be infectious during all four stages, depending on the disease.

Koch's Postulates: - ANS 1. The suspected pathogen must be present in all cases of the
disease and absent from healthy animals.
2. The suspected pathogen must be grown in pure culture.
3. Cells from a pure culture of the suspected pathogen must cause disease in a healthy animal.
4. The suspected pathogen must be re-isolated and shown to be the same as the original.

Define the following terms:
Endemic-
Incidence- - ANS Endemic: constantly present in a population. (The common cold in MN.
Malaria is NOT endemic in MN)

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