Virus Quiz : Test your knowledge

1. Which of the following best explains why some viral infections are “self-limiting” in immunocompetent hosts?

1. The virus loses its genome spontaneously after a few days.
2. Host immune responses control and eliminate the virus without specific treatment.
3. The virus cannot replicate at human body temperature.
4. The virus always mutates into a harmless form.

2. With reference to viral “incubation period”, which of the following is/are correct?

1. It is the interval between exposure to the virus and onset of symptoms.
2. It may vary with infectious dose and host immunity.
3. During incubation, the virus is always absent from the host tissues.

Select the correct answer using the code below:

1. 1 only
2. 1 and 2 only
3. 2 and 3 only
4. 1, 2 and 3

3. Which of the following most accurately defines a “live attenuated viral vaccine”?

1. A vaccine composed of completely inactivated viral particles.
2. A vaccine containing live viruses that have reduced virulence but can still replicate.
3. A vaccine that contains only viral nucleic acid without proteins.
4. A vaccine made solely of recombinant viral proteins with no viral genome.

4. In many viral epidemics, “attack rate” is higher in closed institutions (hostels, barracks) mainly because:

1. Virus becomes genetically more virulent inside buildings.
2. Contact rates and crowding are higher, facilitating transmission.
3. Viruses cannot survive outdoors at all.
4. Residents of such institutions lack any immune response.

5. In the context of viral transmission, “fomite-borne spread” refers to:

1. Transmission via contaminated water only.
2. Transmission through inanimate objects such as doorknobs or utensils.
3. Transmission exclusively by insects.
4. Spread only through airborne droplet nuclei.

6. Which of the following best describes “immune escape variants” of a virus?

1. Variants that completely lack any antigens.
2. Variants with mutations that reduce recognition by pre-existing antibodies or T cells.
3. Variants that cannot infect any host cells.
4. Variants that are always less transmissible.

7. With reference to “mild, asymptomatic or paucisymptomatic infections”, which of the following is/are correct?

1. They can still contribute to viral transmission in the community.
2. They never induce any immune response in the host.
3. They may complicate surveillance because cases are not detected clinically.

Select the correct answer using the code below:

1. 1 and 2 only
2. 1 and 3 only
3. 2 and 3 only
4. 1, 2 and 3

8. In laboratory diagnosis of viral infections, “seroconversion” refers to:

1. Change of viral genome from RNA to DNA.
2. Development of detectable specific antibodies in the blood following infection or vaccination.
3. Conversion of an acute infection into a chronic one.
4. Change from one viral serotype to another inside the same host.

9. Which of the following best describes “case fatality rate” (CFR) for a viral disease?

1. Number of deaths due to the disease divided by total population at risk.
2. Number of deaths due to the disease divided by number of confirmed cases of that disease.
3. Number of infections (symptomatic and asymptomatic) divided by total deaths.
4. Number of hospitalized cases divided by total infections.

10. For a respiratory virus with R₀ around 3, which of the following is the closest theoretical herd immunity threshold (HIT) in an idealized setting with perfect vaccine efficacy?

1. About 25%
2. About 33%
3. About 67%
4. About 90%