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Chapter 13

Viruses, Viroids, and Prions
STUDY
PLAY
A commensal bacterium
May be an opportunistic pathogen
Which of the following statements is true
A. Symbiosis refers to different organisms living together.
B. Members of a symbiotic relationship cannot live without each other
C. A parasite is not in symbiosis with its host.
D. Symbiosis refers to different organisms living together and benefiting from each other.
E. At least one member must benefit in a symbiotic relationship.
A. Symbiosis refers to different organisms living together.
A nosocomial infection is
Always present but is inapparent at the time of hospitalization.
The major significance of Koch's work was that
Microorganisms cause disease
Koch's postulates don't apply to all diseases because
Not all diseases are caused by microorganisms
Which of the following diseases is NOT spread by droplet infection?
A. Botulism
B. Tuberculosis
C. Measles
D. Common cold
E. Diphtheria
Botulism
Mechanical transmission differs from biological transmission in that mechanical transmission
Doesn't involve specific diseases
Which of the following definitions is incorrect?
A. Endemic - Disease constantly present in population
B. Epidemic - fraction of the population having a disease at a specific time
C. Pandemic - affects a large number of people in the world in a short time.
D. Sporadic - affects population occasionally.
E. Incidence - number of new cases of a disease
Epidemic - fraction of the population having a disease at a specific time
Which infection can cause septicemia?
Focal infection
Which type of infection can be caused by septicemia?
Systemic infection
Koch observed Bacillis anthracis multiplying in the blood of cattle. What is this condition called?
Septicemia
Which does NOT contribute to the incidence of nosocomial infections?
Gram-negative cell walls
Transient microbiota differ from normal microbiota because transient microbiota
Are present for a relatively short time
Which statement about nosocomial infections is false
A. They occur in compromised patients
B. They are casued by opportunists
C. They are caused by drug-resistant bacteria
D. They are caused by normal microbiota
E. The patient was infected before hospitalization.
The patient was infected before hospitalization
Regular washing with antibacterial agents is the removal of normal microbiota which can result in
Increased suseptibility to disease
Which is NOT a resevior of infection?
A. Sick person
B. Healthy person
C. Sick animal
D. Hospital
E. All can be reseviors of infection
All can be reseviors of infection
Which is NOT a communicable disease?
A. Malaria
B. AIDS
C. Tuberculosis
D. Tetanus
E. Typhoid fever
Tetanus
Which of the following is a fomite?
A. Water
B. Droplets from a sneeze
C. Pus
D. Insects
E. Hypodermic needle
Hypodermic needle
Which statement is false about biological tramsmission?
A. The pathogen reproduces in the vector
B. The pathogen may enter the host in the vector's feces
C. Houseflies are an important vector
D. The pathogen may be injected by the bite of the vector
E. The pathogen may require the vector as a host
Houseflies are an important vector
Which of the following definitions is incorrect?
A. Acute - a short-lasting primary infection
B. Inapparent - infection characteristic of a carrier state
C. Chronic - a disease that develops slowly and lasts for months
D. Primary infection - an initial illness
E. Secondary infection - a long-lasting illness
Secondary infection - a long-lasting illness
Symptoms of disease differ from signs of disease in that symptoms
Are changes felt by the patient
The science that deals with when diseases occur and how they are transmitted is called
Epidemiology
Graph of influenza during a typical year indicates the endemic level
B
Emergence of infectious diseases can be due to the following except
A. Antibiotic resistance
B. Climatic changes
C. Digging up soil
D. Microbes trying to cause disease
E. Travel
Microbes trying to cause disease
Which of the following pairs is mismatched
A. Malaria - vector
B. Salmonellosis - vehicle transmission
C. Syphilis - direct contact
D. Influenza - droplet infection
E. All are correctly matched
All are correctly matched
Which of the following can contribute to postoperative infections?
A. Using syringes more that once
B. Normal microbiota on the operating room staff
C. Errors in aseptic technique
D. Antibiotic resistance
E. All of the above
All of the above
What is the endemic level of rotavirus infections? (according to figure 14.2)
Approximately 20%
A cold transmitted by a facial tissue is an example of
Vehicle transmission
Influenza transmitted by an unprotected sneeze is an example of
Droplet transmission
A sexually transmitted disease is an example of
Direct contact
Gastroenteritis acquired from roast beef is an example of
Direct contact
A needlestick is an example of
Fomite
Legionellosis transmitted by a grocery story mist machine is an example of
Vehicle transmission
Plague transmitted by a flea is an example of
Vector
The most likely mode of transmission of pneumonic plague between humans is
Droplet transmission
Situation 14.1
239 cases of pneumonia in a town of 300 w/i a 6 month period along with a confirmed case of positive result for antibodies against Coxiella burnetti in sheep which 20 out of 2000 tested, 15 were positive. Weather with wind from the northwest where the sheep were kept and rainfall was factored in
This is an example of
Zoonosis
The etiologic agent of the disease in Situation 14.1 is
Coxiella burnetti
In Situation 14.1 the method of transmission of this disease was
Vehicle transmission
Which is NOT an example of microbial antagonism?
A. Acid production by bacteria
B. Bacteriocin production
C. Bacteria occupying host receptors
D. bacteria causing disease
E. Bacteria producing vitamin K
Bacteria causing disease
The yeast Candida albicans does not normally cause disease because of
Antagonistic bacteria
Haemophilus bacteria require heme protein produced by Staphylococcus bacteria. This is an example of
Synergism
Which of the following is NOT a zoonosis?
A. Cat-scratch disease
B. Hantavirus pulmonary syndrome
C. Rabies
D. Tapeworm
E. All are zoonosis
All are zoonosis
Pseudomonas bacteria colonized the bile duct of a patient following his liver transplant surgery. This is an example of
Nosocomial infection
Figure 14.3 shows incidence of polio in the United States. The period between 1945-1955 indicates
An epidemic level
Which of the following statements is false?
A. Antimicrobial therapy for hemodialysis-associated infections increases antibiotic resistance.
B. S. aureus is differentiated from other mannitol+ cocci by the coagulase test
C. The M in MRSA stands for mannitol
D. USA100 accounts for most hospital-acquired MRSA.
E. USA300 accounts for most community-acquired MRSA
The M in MRSA stands for mannitol
Endemic
A disease that is constantly present in a population
Epidemic
Many people in a given area acquire a certain disease in a relatively short period
Pandemic
A disease that affects a large number of people in the world in a short time
Sporadic
A disease that affects a population occasionally
Incidence
The number of new cases of a disease
Which of the following statements is(are) wholly characteristic(s) of viruses?
A. Viruses contain either DNA or RNA; and they undergo binary fusion.
B. Viruses' requirements for the availability of cellular factors, within the potential
host cell, required for viral multiplication determine its morphology.
C. Viruses possess enzymes for protein synthesis and ATP generation.
D. Requirements for a virus to specifically attach to the host cell determine its
particular host range.
D. Requirements for a virus to specifically attach to the host cell determine its
particular host range.
Hemagglutination is associated with which structural component of certain viruses?
Spikes
If a patient exhibits symptoms associated with the common cold and upper respiratory tract infections, which
viral genus is the likely culprit?
Coronavirus
Which of the following is true regarding cultivation and isolation of animal viruses?
A. Primary cell lines are transformed cells that can be maintained through an
indefinite number of generations.
B. Diploid cell lines are widely used for culturing viruses that require a human
host.
C. Mice provide a reliable model for studying viral replication and for developing
vaccines.
D. The preferred and widely used method of viral isolation and growth is via
growth in an embryonated egg.
B. Diploid cell lines are widely used for culturing viruses that require a human
host.
Regarding the biosynthesis of DNA viruses, components of which virus family are synthesized in the host cell
cytoplasm?
Poxviridae
Which of the following virus families transcribes viral DNA in the host nucleus, with host enzymes, and uses reverse transcriptase to make viral DNA from mRNA?
A. Reoviridae
B. Papovaviridae
C. Parvoviridae
D. Hepadnaviridae
D. Hepadnaviridae
What is the correct sequence of events during the replication of a DNA-containing animal virus?
1 - Virions mature.
2 - Capsid proteins are synthesized.
3 - Virions are released.
4 - Early viral proteins are encoded as viral DNA is transcribed.
5 - Virion enters host cell and its DNA is uncoated.
6 - Virion attaches to host cell.
7 - Viral DNA is replicated, and some viral proteins are made.
6-5-4-7-2-1-3
Which clinical feature or special feature applies to the papovaviridae family of viruses?
A. Its viruses induce tumors as host cells may proliferate.
B. Viral DNA is transcribed, by cellular enzymes, in the nucleus of the host cell.
C. Its papillomavirus genus produces warts in humans.
D. Its viruses induce tumors as host cells may proliferate. Its papillomavirus genus produces warts in human. Viral DNA is transcribed, by cellular enzymes, in the nucleus of the host cell.
D. Its viruses induce tumors as host cells may proliferate. Its papillomavirus genus produces warts in human. Viral DNA is transcribed, by cellular enzymes, in the nucleus of the host cell.
Which is the correct sequence of steps regarding the multiplication and inheritance processes of the
Retroviridae?
1 - Provirus transcription may occur.
2 - Fusion between viral envelope and plasma membrane.
3 - Reverse transcriptase copies viral RNA to produce double-stranded DNA.
4 - Mature retrovirus leaves the host cell.
5 - Uncoating releases viral RNA genomes and enzymes.
6 - Viral DNA is transported into the host nucleus.
7 - Viral proteins are processed by viral protease.
2-5-3-6-1-7-4
Which of the following statements regarding lysogeny is true?
a)During lysogeny, most phage genes are repressed by repressor proteins that are
products of the host DNA.
b)Occasionally, rare spontaneous events, such as ultraviolet light, can lead to rapid
incorporation of phage DNA into the host cell DNA.
c)During lysogeny, phage genes are turned on, in order to synthesize new virions.
d)During lysogeny, most phage genes are repressed by two repressor proteins that are
phage gene products.
b)During lysogeny, most phage genes are repressed by two repressor proteins that are phage gene products.
Regarding the multiplication pathways of RNA-containing viruses, which of the following are double-stranded RNA viruses that must use sense strand mRNA to code for proteins?
Reoviridae
What is true regarding latent viral infections is true?
Changes in the immune (T-cell lymphocyte) response can activate certain latent viruses.
Which statement is incorrect regarding the biosynthesis of DNA and RNA viruses?
a)Togaviridae use viral RNA as a template for synthesizing RNA polymerase, which copies sense strand RNA to make mRNA in the cytoplasm.
b)Viral DNA is made from mRNA, via reverse transcriptase, in hepadnaviridae.
c)Reoviruses make mRNA by copying antisense strand RNA in the cytoplasm.
d)Parvoviridae use cellular enzymes to transcribe viral DNA in the nucleus.
a)Togaviridae use viral RNA as a template for synthesizing RNA polymerase, which copies sense strand RNA to make mRNA in the cytoplasm.
Which of the following is a characteristic of the infectious diseases caused by prions?
Host cellular prion proteins (PrPC) are converted into scrapie proteins (PrPSc).
How does specialized transduction differ from regular lysogeny?
The prophage in specialized transduction carries with it pieces of the host chromosomal DNA.
What happens to the packaged DNA of a specialized transduced phage when it infects a new recipient cell?
The host DNA integrates, with the prophage, into the new recipient chromosome.
How can specialized transduction contribute to the transfer of antibiotic resistance genes in a bacterial population?
The prophage takes an antibiotic resistance gene with it and is packaged with the newly synthesized viral DNA.
How do naked viruses differ from enveloped viruses in their attachment/penetration phase?
Their nucleic acids are injected into the cell
Which virus employs the use of an RNA-dependent RNA polymerase?
+RNA viruses
Which of the following viruses is transcribed from RNA to DNA to RNA during the replication cycle?
Retroviruses
Which type of virus would product viral glycoproteins to be expressed on the host cell membrane?
Enveloped viruses
Which of the following can be used as messenger RNA?
a)ssDNA
b)+RNA
c)-RNA
+RNA
How are viruses different from cells?
They require a host in order to reproduce.
What is the function of the structural elements of a virus?
To package and protect the viral genome
Lysogenic viral DNA integrating into the host genome is referred to as
a prophage
Which of the following events might trigger induction of a temperate bacteriophage?
Exposure to UV light
How is the lytic cycle different from the lysogenic cycle with respect to the infected host cell?
The host cell dies during the lytic stage.
What is the fate of the prophage during the lysogenic stage?
It is copied every time the host DNA replicates.
In which stage is the viral DNA introduced into the cell?
Penetration
In which stage does formation of mature viruses occur?
Assembly
The host DNA is usually degraded during which stage?
Biosynthesis
The virus would not be able to infect new hosts
What would be the fate of a lytic bacteriophage if the host cell died prior to the assembly stage?
An animal diseases that is human disease caused by prions?
Creutzfeldt-Jakob disease (CJD)
The normal function of the PrP protein in mammals is believed to be:
assisting in normal synaptic development and function
How do normal prion proteins (PrP) differ from the infectious prion pr
Normal PrP have alpha-helices; infectious PrP have beta-pleated sheets
How does the number of infectious prions increase?
Prions transform normal proteins into the misfolded beta-pleated sheet configuration; therefore, prions multiply by conversion.
Why are the beta-pleated multimers of PrP potentially pathogenic?
The multimers are more stable and resistant to protease.
A prion diseases that is found in deer and elk?
Chronic wasting disease
A prion diseases also known as laughing disease?
Kuru
Which of the following conditions in humans is linked to bovine spongiform encephalopathy?
Variant Creutzfeldt-Jakob disease
What part of the nervous system is most affected by fatal familial insomnia?
Thalamus
Where does the name "scrapie" come from?
The prion disorder causes infected sheep to scrape against objects until their skin is raw.
From which phrase is the term "prions" derived?
Proteinaceous infectious particles
In what year did Stanley Prusiner discover prions?
1982
Which disease did Stanley Prusiner first identify as being caused by prions?
Scrapie
How are prions different from other infectious agents?
They lack nucleic acid
Contributes to antigenic shift in influenza viruses?
Segmented genome
Most RNA viruses carry which of the following enzymes?
RNA-dependent RNA polymerase
Most likely a product of an early gene?
DNA polymerase
Nontoxic strains of Vibrio cholerae can become toxic when they are in the human intestine with toxic strains of bacteria. This suggests that the toxin genes are acquired by
Transduction
Some viruses, such as human herpesvirus 1, exist in a cell without causing symptoms; these are called
Latent viruses
Which of the following is not characteristic of viroids?
a)Its internally paired nucleotides' three-dimensional structure helps protect it from attack by cellular enzymes.
b)There are similarities between the base sequences of viroids and exons, resulting in the hypothesis that viroids evolved from exons.
c)Viroids are short pieces of naked RNA.
d)Viroids are typically 300 to 400 nucleotides long.
b)There are similarities between the base sequences of viroids and exons, resulting in the hypothesis that viroids evolved from exons.
How do viruses differ from bacteria?
Viruses are filterable
Viruses are not composed of cells
Which of the following statements provides the most significant support for the idea that viruses are nonliving chemicals?
a)They are not composed of cells.
b)They are filterable.
c)They cause diseases similar to those caused by chemicals.
d)They cannot reproduce themselves outside a host.
e)They are chemically simple.
d)They cannot reproduce themselves outside a host.
Which of the following statements about spikes is false?
a)They are used for absorption.
b)They are used for penetration.
c)They may cause hemagglutination.
d)They are found only on enveloped viruses.
b)They are used for penetration
What is used as criteria to classify viruses?
Morphology
Nucleic acid
Size
Number of capsomeres
Which of the following is NOT a method of culturing viruses?
a)In laboratory animals
b)In cell culture
c)In embryonated eggs
d)In culture media
e)None of the above
d)In culture media
The definition of lysogeny is
Phage DNA is incorporated into host cell DNA.
A viroid is
A nonenveloped, infectious piece of RNA
A clear area against a confluent "lawn" of bacteria is called a
Plaque
The most common route of accidental AIDS transmission to health care workers is
needlestick
An example of a latent viral infection is
cold sores
Which of the following contributes to the difficulty in establishing the etiology of cancer?
a)Most viral particles can infect cells without inducing cancer.
b)Cancer may not develop until long after infection.
c)Cancers do not seem to be contagious.
d)Viruses are difficult to observe.
e)All of the above.
e) all of the above
An envelope is acquired during which step?
Release
An infectious protein is a
prion
What is the first step in biosynthesis of a virus with a - strand of RNA?
Synthesis of double-stranded RNA from an RNA template
Lysogeny can result in all of the following EXCEPT
a)Immunity to reinfection by any phage.
b)Acquisition of new characteristics by the host cell.
c)Immunity to reinfection by the same phage.
d)Transduction of specific genes.
e)None of the above.
a)Immunity to reinfection by any phage.
Which of the following statements is false?
a)A prophage is phage DNA inserted into a bacterial chromosome.
b)A prophage can pop out of the chromosome.
c)The prophage makes the host cell immune to infection by other phages.
d)A prophage may result in new properties of the host cell.
e)Prophage genes are represented by a repressor protein coded for by the prophage.
c)The prophage makes the host cell immune to infection by other phages.
A persistent infection is an infection in which
the disease process occurs gradually over a long period
What is necessary for replication of a prion?
pSc
Continuous cell lines differ from primary cell lines in that
Continuous cell lines can be maintained through an indefinite number of generations.
The most conclusive evidence that viruses cause cancers is provided by
cancer following injection of cell-free filtrates
Bacteriophages derive all of the following from the host cell EXCEPT
a)tRNA.
b)Lysozyme.
c)Amino acids.
d)Nucleotides.
e)A.T.P.
b)Lysozyme
Generally, in a DNA-containing virus infection, the host animal cell supplies all of the following EXCEPT
a)RNA polymerase.
b)DNA polymerase.
c)Nucleotides.
d)tRNA.
e)All of the above are supplied by the host animal cell.
b)DNA polymerase
Put the following in the correct order for DNA-virus replication:
1-Maturation; 2-DNA synthesis; 3-Transcription; 4-Translation.
2, 3, 4, 1
A viral species is a group of viruses that
Have the same genetic information and ecological niche.
Viruses that have reverse transcriptase are in the
Hepadnaviridae and Retroviridae
Which of the following statements about viruses is false?
a)Viruses contain DNA or RNA but never both.
b)Viruses use their own catabolic enzymes.
c)Viruses use the anabolic machinery of the cell.
d)Viruses contain a protein coat.
e)Viruses have genes.
b)Viruses use their own catabolic enzymes.