Q: Which of the following equations correctly represents the calculation of viral titer in a plaque assay?

$$\text{Viral\ titer\ (PFU/ml)} = \frac{\text{Number\ of\ plaques}}{\text{Dilution\ factor} \times \text{Volume\ plated\ (ml)}}$$

Question 1

Which of the following statements best describes why viruses are considered obligate intracellular pathogens?

Accepted Answer

They require a host cell's machinery to replicate and produce new virions.

Question 2

A virus with a helical capsid structure is most likely to appear as which of the following shapes under an electron microscope?

Accepted Answer

A hollow tube or rod-like structure

Question 3

Which of the following best explains why RNA viruses tend to mutate more rapidly than DNA viruses?

Accepted Answer

RNA-dependent RNA polymerases lack proofreading activity.

Question 4

A patient is diagnosed with a viral infection that is characterized by periods of dormancy and occasional flare-ups of symptoms. Which type of infection is this most likely to be?

Accepted Answer

Latent persistent infection

Question 5

Which of the following is a correct description of antigenic shift in influenza viruses?

Accepted Answer

A major genetic reassortment resulting in a new viral strain with novel HA and NA spikes

Question 6

Which of the following best describes the function of viral spikes (peplomers)?

Accepted Answer

They mediate attachment to specific host cell receptors.

Question 7

A bacteriophage infects a bacterial cell and immediately begins producing new virions, ultimately lysing the host cell. Which replication pathway is being described?

Accepted Answer

Lytic replication pathway

Question 8

Which of the following equations correctly represents the calculation of viral titer in a plaque assay?

Accepted Answer

$$	ext{Viral\ titer\ (PFU/ml)} = \frac{	ext{Number\ of\ plaques}}{	ext{Dilution\ factor} 	imes 	ext{Volume\ plated\ (ml)}}$$

Question 9

Which of the following viruses is most likely to be classified as oncogenic and associated with human cancers?

Accepted Answer

Human papillomavirus (HPV)

Question 10

A laboratory is using an ELISA to detect the presence of viral antigens in a patient sample. Which of the following is a limitation of this method?

Accepted Answer

It may not detect viruses that have undergone significant antigenic shift.

Question 11

Which of the following best explains why prions are unique among infectious agents?

Accepted Answer

They are infectious proteins that lack genetic material.

Question 12

A patient is infected with a single-stranded negative-sense RNA virus. Which enzyme is required for this virus to produce mRNA in the host cell?

Accepted Answer

RNA-dependent RNA polymerase

Question 13

Which of the following antiviral drugs acts by inhibiting the release of influenza virions from the host cell surface?

Accepted Answer

Oseltamivir

Question 14

Which of the following best describes the process of phage conversion?

Accepted Answer

A bacterium acquires new pathogenic traits due to the presence of a prophage.

Question 15

Which of the following is a key difference between enveloped and naked animal viruses during the release step of replication?

Accepted Answer

Enveloped viruses are released by budding, while naked viruses are released by cell lysis.

Question 16

A virus is found to have a segmented, double-stranded RNA genome. Which of the following virus families is it most likely to belong to?

Accepted Answer

Reoviridae

Question 17

Which of the following best describes the host range of a virus?

Accepted Answer

The collection of species that a virus can infect

Question 18

Which of the following is a medically important DNA virus family that can cause warts and is associated with cervical cancer?

Accepted Answer

Papillomaviridae

Question 19

Which of the following best explains why vaccines are an effective means to limit viral infection?

Accepted Answer

They train the immune system to recognize and respond to specific viral antigens.

Question 20

A patient is exposed to a virus and receives a laboratory-prepared mixture of injectable antibodies shortly after exposure. This is an example of which of the following?

Accepted Answer

Postexposure prophylaxis

Viruses and Prions: Structure, Classification, Replication, and Clinical Aspects

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