Questions

Viral Exanthems — Questions

Study questions for Viral Exanthems.

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.

17 questions: 13 MCQ, 4 written.

High-priority (past-paper) questions only

a. Diagnosis. Smallpox (variola), suggested by a synchronous vesiculopustular rash healing with scarring, the lesions all at the same stage.

b. Classification. Family Poxviridae, genus Orthopoxvirus, species variola virus.

c. Another genus. For example Parapoxvirus (orf, milker’s nodule) or Molluscipoxvirus (molluscum contagiosum).

d. Modern threat. Although eradicated in 1980, variola poses a bioterrorism threat because the population is now largely unvaccinated and susceptible.

Agent. Molluscum contagiosum virus, a poxvirus (genus Molluscipoxvirus).
Distribution. Common worldwide, chiefly in children.
Transmission. By direct skin-to-skin contact and fomites, and by autoinoculation.
In adults. Frequently sexually transmitted, giving genital lesions.
In immunocompromise. Florid, widespread disease with hundreds of lesions in advanced HIV, often with facial involvement.

A complete answer names the common causes, gives discriminating clinical features, uses the laboratory sparingly and correctly, and identifies measles as the eradication target.

Common viral causes. The commonest are measles, rubella and parvovirus B19 (erythema infectiosum), with HHV-6 (roseola) and the enteroviruses also frequent.

Distinguishing features. Measles gives a prodrome of fever, cough, coryza and conjunctivitis with Koplik spots, then a rash spreading from the head downward. Rubella is milder with a finer rash and posterior auricular and suboccipital lymphadenopathy. Parvovirus B19 gives the slapped-cheek face and a lacy limb rash.

Laboratory. Most cases are diagnosed clinically. Where confirmation is needed, serum IgM (or a rising IgG) confirms measles, rubella and parvovirus, with PCR or reference-laboratory testing reserved for unclear or public-health-important cases. Suspected measles is notified and the child isolated, so testing serves infection control as much as the individual.

Eradication target. Measles is targeted for global eradication: humans are the only reservoir, there is no animal host, and a highly effective live vaccine gives durable immunity, so interrupting transmission is feasible.

A complete answer covers the virus, the clinical picture and its distinction from smallpox, and diagnosis and prevention.

Virus. Mpox virus is an orthopoxvirus of the family Poxviridae, a zoonosis endemic in parts of Africa, and it produces disease resembling a milder smallpox.

Clinical features. After an incubation of about 10 to 14 days come a prodrome of fever, malaise and prominent lymphadenopathy, then a rash that begins on the trunk and spreads peripherally, which may involve the palms, soles and mucous membranes; mortality is around 10%.

Distinction and diagnosis. The lymphadenopathy is characteristic of mpox and was not a feature of smallpox, but the poxviruses can be told apart reliably only by PCR.

Prevention. There is no proven specific treatment, but smallpox vaccination is highly protective.

The measles rash is largely a cell-mediated immune response to virus in the skin, so a child who cannot mount that response may have measles with no rash, which hinders diagnosis.

It is not driven by bacterial superinfection, direct necrosis, maternal antibody or IgE.

Erythema infectiosum (fifth disease), caused by parvovirus B19, gives the slapped-cheek appearance and a lacy reticular limb rash.

Roseola, rubella, measles and scarlet fever produce different rashes and prodromes.

Prominent lymphadenopathy in the prodrome is characteristic of mpox and was not a feature of smallpox, though PCR is needed to separate the poxviruses reliably.

A febrile prodrome, palmar involvement and scarring occur in both.

Varicella lesions appear in crops and are at different stages at any one time (macule, papule, vesicle, pustule, crust), whereas smallpox lesions were all synchronous.

The other options do not describe chickenpox.

Roseola infantum (exanthem subitum, sixth disease) is caused by HHV-6 (and HHV-7): high fever precedes a rash that appears as the fever resolves, and it may provoke a febrile seizure.

The other agents do not show this fever-then-rash sequence.

Molluscum contagiosum, a poxvirus infection, causes umbilicated papules that become florid and widespread in advanced HIV, often with facial involvement.

The other conditions do not give umbilicated papules.

Coxsackievirus A16 (and enterovirus 71) cause hand-foot-and-mouth disease, with vesicles on the palms, soles and buccal mucosa.

The other viruses cause different vesicular or maculopapular eruptions.

Parvovirus B19 infects erythroid progenitors and halts red-cell production, precipitating a transient aplastic crisis in people with chronic haemolysis who depend on brisk erythropoiesis.

It does not cause autoimmune haemolysis, iron overload, polycythaemia or a coagulopathy.

Virus is readily recovered from the fluid of vesicular lesions, whereas maculopapular rashes shed little or no virus, which is why varicella and zoster require contact and airborne precautions.

Some virus is present in lesions generally, but the vesicle fluid is the infectious source, not maculopapular rashes, pustules alone or old crusts.

Postherpetic neuralgia, pain persisting beyond 8 to 12 weeks, is the commonest important complication of shingles, and its risk rises with age.

The other conditions are not complications of herpes zoster.

PCR on vesicle fluid is the most sensitive test and has largely replaced culture for herpes simplex and varicella-zoster.

A Tzanck smear is quick but non-specific, culture is insensitive, and serology and electron microscopy are second-line.

Rubella itself is mild, but infection in early pregnancy causes the congenital rubella syndrome, so control protects the fetus rather than the patient.

Rubella does not typically cause severe patient illness, encephalitis, pneumonia or later reactivation.

The morbilliform measles rash spreads from the forehead and behind the ears downward to the trunk, limbs, palms and soles, following the prodrome and Koplik spots.

Acral onset, cropping, dermatomal confinement and facial sparing describe other eruptions.

High priorityClinical scenarioAn archival photograph from 1970 shows a patient with a generalised rash that progressed through papules to deep-seated pustules, all at the same stage of development, and healed with scarring. (a) What is the most likely clinical diagnosis? (b) Classify the causative virus by family and genus. (c) Name one other genus in this virus family. (d) State the specific threat this virus may pose in modern times. [5]
Model answer
a. Diagnosis. Smallpox (variola), suggested by a synchronous vesiculopustular rash healing with scarring, the lesions all at the same stage.

b. Classification. Family Poxviridae, genus Orthopoxvirus, species variola virus.

c. Another genus. For example Parapoxvirus (orf, milker’s nodule) or Molluscipoxvirus (molluscum contagiosum).

d. Modern threat. Although eradicated in 1980, variola poses a bioterrorism threat because the population is now largely unvaccinated and susceptible.
High prioritySAQWrite short notes on the epidemiology of molluscum contagiosum. [5]
Model answer
- Agent. Molluscum contagiosum virus, a poxvirus (genus Molluscipoxvirus).
- Distribution. Common worldwide, chiefly in children.
- Transmission. By direct skin-to-skin contact and fomites, and by autoinoculation.
- In adults. Frequently sexually transmitted, giving genital lesions.
- In immunocompromise. Florid, widespread disease with hundreds of lesions in advanced HIV, often with facial involvement.
High priorityExam-styleA 5-year-old presents with a febrile maculopapular rash of two days. List three common viral causes; describe distinguishing features for two of them; outline the laboratory investigations with attention to resource stewardship and infection control; and name one viral cause of childhood rash targeted for global eradication with two features that make eradication feasible. [10]
Model answer
A complete answer names the common causes, gives discriminating clinical features, uses the laboratory sparingly and correctly, and identifies measles as the eradication target.

Common viral causes. The commonest are measles, rubella and parvovirus B19 (erythema infectiosum), with HHV-6 (roseola) and the enteroviruses also frequent.

Distinguishing features. Measles gives a prodrome of fever, cough, coryza and conjunctivitis with Koplik spots, then a rash spreading from the head downward. Rubella is milder with a finer rash and posterior auricular and suboccipital lymphadenopathy. Parvovirus B19 gives the slapped-cheek face and a lacy limb rash.

Laboratory. Most cases are diagnosed clinically. Where confirmation is needed, serum IgM (or a rising IgG) confirms measles, rubella and parvovirus, with PCR or reference-laboratory testing reserved for unclear or public-health-important cases. Suspected measles is notified and the child isolated, so testing serves infection control as much as the individual.

Eradication target. Measles is targeted for global eradication: humans are the only reservoir, there is no animal host, and a highly effective live vaccine gives durable immunity, so interrupting transmission is feasible.
High priorityExam-styleWrite short notes on mpox (monkeypox) virus. [10]
Model answer
A complete answer covers the virus, the clinical picture and its distinction from smallpox, and diagnosis and prevention.

Virus. Mpox virus is an orthopoxvirus of the family Poxviridae, a zoonosis endemic in parts of Africa, and it produces disease resembling a milder smallpox.

Clinical features. After an incubation of about 10 to 14 days come a prodrome of fever, malaise and prominent lymphadenopathy, then a rash that begins on the trunk and spreads peripherally, which may involve the palms, soles and mucous membranes; mortality is around 10%.

Distinction and diagnosis. The lymphadenopathy is characteristic of mpox and was not a feature of smallpox, but the poxviruses can be told apart reliably only by PCR.

Prevention. There is no proven specific treatment, but smallpox vaccination is highly protective.
MCQ
A child with defective cell-mediated immunity develops measles without a rash. The best explanation is that the measles rash:
- A. Requires bacterial superinfection
- B. Reflects a cell-mediated immune response
- C. Is caused by direct epidermal necrosis
- D. Depends on maternal antibody
- E. Is an IgE-mediated allergic reaction
Show answer
Correct answer: B
The measles rash is largely a cell-mediated immune response to virus in the skin, so a child who cannot mount that response may have measles with no rash, which hinders diagnosis.

It is not driven by bacterial superinfection, direct necrosis, maternal antibody or IgE.
MCQ
A child with flushed cheeks, circumoral pallor and a lacy rash on the limbs most likely has:
- A. Roseola infantum
- B. Erythema infectiosum
- C. Rubella
- D. Measles
- E. Scarlet fever
Show answer
Correct answer: B
Erythema infectiosum (fifth disease), caused by parvovirus B19, gives the slapped-cheek appearance and a lacy reticular limb rash.

Roseola, rubella, measles and scarlet fever produce different rashes and prodromes.
MCQ
A clinical feature that helps distinguish mpox from smallpox is:
- A. A synchronous rash
- B. Prominent lymphadenopathy
- C. Involvement of the palms
- D. Healing with scarring
- E. A febrile prodrome
Show answer
Correct answer: B
Prominent lymphadenopathy in the prodrome is characteristic of mpox and was not a feature of smallpox, though PCR is needed to separate the poxviruses reliably.

A febrile prodrome, palmar involvement and scarring occur in both.
MCQ
A feature that distinguished chickenpox from smallpox was that in chickenpox the lesions:
- A. Were confined to the palms and soles
- B. Were all at the same stage
- C. Never formed vesicles
- D. Were at different stages of evolution
- E. Healed without crusting
Show answer
Correct answer: D
Varicella lesions appear in crops and are at different stages at any one time (macule, papule, vesicle, pustule, crust), whereas smallpox lesions were all synchronous.

The other options do not describe chickenpox.
MCQ
An infant has several days of high fever, then a rose-pink truncal rash appears as the fever breaks. The likely cause is:
- A. Measles virus
- B. Parvovirus B19
- C. Human herpesvirus 6
- D. Rubella virus
- E. Coxsackievirus A16
Show answer
Correct answer: C
Roseola infantum (exanthem subitum, sixth disease) is caused by HHV-6 (and HHV-7): high fever precedes a rash that appears as the fever resolves, and it may provoke a febrile seizure.

The other agents do not show this fever-then-rash sequence.
MCQ
Dome-shaped umbilicated skin papules that are florid and widespread in a patient with advanced HIV are most likely:
- A. Herpes zoster
- B. Varicella
- C. Erythema infectiosum
- D. Herpangina
- E. Molluscum contagiosum
Show answer
Correct answer: E
Molluscum contagiosum, a poxvirus infection, causes umbilicated papules that become florid and widespread in advanced HIV, often with facial involvement.

The other conditions do not give umbilicated papules.
MCQ
Hand-foot-and-mouth disease is most commonly caused by:
- A. Herpes simplex virus
- B. Varicella-zoster virus
- C. Measles virus
- D. Parvovirus B19
- E. Coxsackievirus A16
Show answer
Correct answer: E
Coxsackievirus A16 (and enterovirus 71) cause hand-foot-and-mouth disease, with vesicles on the palms, soles and buccal mucosa.

The other viruses cause different vesicular or maculopapular eruptions.
MCQ
In a patient with chronic haemolytic anaemia, parvovirus B19 characteristically causes:
- A. Autoimmune haemolysis
- B. Iron overload
- C. Polycythaemia
- D. Transient aplastic crisis
- E. Disseminated coagulopathy
Show answer
Correct answer: D
Parvovirus B19 infects erythroid progenitors and halts red-cell production, precipitating a transient aplastic crisis in people with chronic haemolysis who depend on brisk erythropoiesis.

It does not cause autoimmune haemolysis, iron overload, polycythaemia or a coagulopathy.
MCQ
Regarding infectivity of viral skin lesions:
- A. Maculopapular rashes shed abundant virus
- B. Virus is not shed from any skin lesion
- C. Vesicular lesions shed infectious virus
- D. Only pustules are infectious
- E. Crusts remain highly infectious for months
Show answer
Correct answer: C
Virus is readily recovered from the fluid of vesicular lesions, whereas maculopapular rashes shed little or no virus, which is why varicella and zoster require contact and airborne precautions.

Some virus is present in lesions generally, but the vesicle fluid is the infectious source, not maculopapular rashes, pustules alone or old crusts.
MCQ
The commonest important complication of herpes zoster is:
- A. Dilated cardiomyopathy
- B. Aplastic crisis
- C. Postherpetic neuralgia
- D. Congenital malformation
- E. Nephrotic syndrome
Show answer
Correct answer: C
Postherpetic neuralgia, pain persisting beyond 8 to 12 weeks, is the commonest important complication of shingles, and its risk rises with age.

The other conditions are not complications of herpes zoster.
MCQ
The most sensitive test to confirm the cause of a vesicular rash is:
- A. PCR of vesicle fluid
- B. Viral culture of the vesicle
- C. A Tzanck smear
- D. Acute-phase serology
- E. Electron microscopy
Show answer
Correct answer: A
PCR on vesicle fluid is the most sensitive test and has largely replaced culture for herpes simplex and varicella-zoster.

A Tzanck smear is quick but non-specific, culture is insensitive, and serology and electron microscopy are second-line.
MCQ
The principal reason to control rubella is that infection:
- A. In early pregnancy harms the fetus
- B. Causes severe disease in the patient
- C. Frequently leads to encephalitis
- D. Commonly causes pneumonia
- E. Reactivates as shingles later
Show answer
Correct answer: A
Rubella itself is mild, but infection in early pregnancy causes the congenital rubella syndrome, so control protects the fetus rather than the patient.

Rubella does not typically cause severe patient illness, encephalitis, pneumonia or later reactivation.
MCQ
The rash of measles characteristically:
- A. Spreads downward from the head
- B. Begins on the hands and feet
- C. Appears in asynchronous crops
- D. Is confined to a single dermatome
- E. Spares the face and neck
Show answer
Correct answer: A
The morbilliform measles rash spreads from the forehead and behind the ears downward to the trunk, limbs, palms and soles, following the prodrome and Koplik spots.

Acral onset, cropping, dermatomal confinement and facial sparing describe other eruptions.