Questions

Patterns of Infection — Questions

Study questions for Patterns of Infection.

Mock Exam mode

Sit this set one question at a time. Multiple-choice questions mark themselves; written questions reveal a tickable mark scheme so you can score your own answer. You get a combined score at the end.

3 questions: 2 MCQ, 1 written.

Herpes simplex virus is carried as a truly latent, non-replicating genome in sensory neurons, so its return to active replication is reactivation, the cellular event that proceeds from genuine latency.

Recrudescence is better reserved for the clinical flare of a persistent, low-level infection that has continued to replicate rather than one emerging from true latency. Recurrence is the repeat clinical episode that results, the cold sore itself, not the underlying event. Reinfection would be a fresh infection acquired anew from outside, not return of the resident virus. Primary infection is the first encounter, which has long since passed.

Susceptibility and permissiveness are independent: a cell is susceptible if it carries the functional receptor for entry and permissive if it can also support the full replication cycle. Here the virus enters (so the cell is susceptible) but cannot complete replication (so it is non-permissive), and the result is an abortive infection, genome in and no progeny out.

The other options misuse the pair. Entry requires susceptibility, so a permissive but not susceptible cell is contradictory; a productive or lytic infection needs both properties; and latency and chronic infection are patterns of persistence, not the description of a single abortive event.

Viral infections are classified on two axes: duration (transient or persistent) and extent (localised to the entry surface or systemic, spreading through the body). Crossing the two gives four patterns.

Pattern	Example
Transient localised	The common cold (rhinoviruses); influenza; rotavirus gastroenteritis
Transient systemic	Measles; varicella; mumps
Persistent localised	Papillomavirus warts
Persistent systemic	Herpesvirus latency; chronic hepatitis B and C; HIV (human immunodeficiency virus)

A transient infection is cleared once the immune response develops, usually leaving immunity. A persistent infection is not cleared, and it subdivides by the nature of the ongoing infection:

Latent, in which the genome lies dormant in a long-lived cell with no infectious virus made between episodes, but with the capacity to reactivate, as in the herpesviruses.

Chronic active, in which the virus continues to replicate, often abundantly, with slowly progressive or delayed disease, as in hepatitis B, hepatitis C, and HIV.

A separate group, the persistent infections with rare late complications, sits within the systemic category: an apparently resolved infection that produces a delayed disease years later, as measles does in subacute sclerosing panencephalitis (SSPE). Overlaid on every pattern is the distinction between asymptomatic (subclinical) and symptomatic infection.

MCQ
A patient with lifelong latent herpes simplex virus develops a cold sore after sun exposure. The return of the dormant virus to active replication is best termed:
- A. Reactivation
- B. Recrudescence
- C. Recurrence
- D. Reinfection
- E. Primary infection
Show answer
Correct answer: A
Herpes simplex virus is carried as a truly latent, non-replicating genome in sensory neurons, so its return to active replication is reactivation, the cellular event that proceeds from genuine latency.

Recrudescence is better reserved for the clinical flare of a persistent, low-level infection that has continued to replicate rather than one emerging from true latency. Recurrence is the repeat clinical episode that results, the cold sore itself, not the underlying event. Reinfection would be a fresh infection acquired anew from outside, not return of the resident virus. Primary infection is the first encounter, which has long since passed.
MCQ
A virus enters a cell that bears its receptor but cannot complete replication, so no progeny are produced. This cell is best described as:
- A. Permissive but not susceptible, giving a productive infection
- B. Susceptible and permissive, giving a lytic infection
- C. Susceptible but non-permissive, giving an abortive infection
- D. Both susceptible and permissive, giving a latent infection
- E. Neither susceptible nor permissive, giving a chronic infection
Show answer
Correct answer: C
Susceptibility and permissiveness are independent: a cell is susceptible if it carries the functional receptor for entry and permissive if it can also support the full replication cycle. Here the virus enters (so the cell is susceptible) but cannot complete replication (so it is non-permissive), and the result is an abortive infection, genome in and no progeny out.

The other options misuse the pair. Entry requires susceptibility, so a permissive but not susceptible cell is contradictory; a productive or lytic infection needs both properties; and latency and chronic infection are patterns of persistence, not the description of a single abortive event.

Exam-styleClassify the patterns of viral infection and give an example of each. [6]

Model answer

Pattern	Example
Transient localised	The common cold (rhinoviruses); influenza; rotavirus gastroenteritis
Transient systemic	Measles; varicella; mumps
Persistent localised	Papillomavirus warts
Persistent systemic	Herpesvirus latency; chronic hepatitis B and C; HIV (human immunodeficiency virus)

A transient infection is cleared once the immune response develops, usually leaving immunity. A persistent infection is not cleared, and it subdivides by the nature of the ongoing infection:

Latent, in which the genome lies dormant in a long-lived cell with no infectious virus made between episodes, but with the capacity to reactivate, as in the herpesviruses.

Chronic active, in which the virus continues to replicate, often abundantly, with slowly progressive or delayed disease, as in hepatitis B, hepatitis C, and HIV.