Dermatology MCQ - Viral Infections - Roseola infantum

A 9-month-old infant is brought to the clinic for a high fever (103°F) that resolved abruptly after 3 days. Following the fever, a blanching, pinkish-red maculopapular rash appeared on the trunk and spread to the neck and extremities. The child is now playful and well-hydrated. Which of the following is the most likely causative agent and its primary mode of transmission?

A) Human herpesvirus 6 (HHV-6); respiratory droplets
B) Parvovirus B19; respiratory droplets
C) Measles virus; airborne transmission
D) Group A Streptococcus; direct contact
E) Coxsackievirus A16; fecal-oral route

Correct Answer: A) Human herpesvirus 6 (HHV-6); respiratory droplets

Explanation

This presentation is classic for roseola infantum (also known as exanthem subitum or sixth disease).

Key Clinical Features of Roseola Infantum:

• Age: Primarily affects infants and children 6 months to 2 years old.

• Prodrome: High fever (often >103°F) for 3-5 days in an otherwise well-appearing child.

• Rash: Once the fever resolves abruptly, a blanching, erythematous maculopapular rash appears, starting on the trunk and spreading to the neck and extremities. The rash is non-pruritic and fades within 1-2 days.

• "The child is fine now" sign: The child becomes playful and comfortable once the rash appears, as the fever has resolved.

Virologic Features:

• Causative Agent: Human herpesvirus 6 (HHV-6) is the primary cause (90% of cases). HHV-7 can cause a similar illness.

• Transmission: Primarily through respiratory droplets from asymptomatic shedding or infected individuals.

• Pathogenesis: After primary infection, HHV-6 establishes latency in monocytes and salivary glands.

Why Not the Other Options?

• (B) Parvovirus B19: Causes erythema infectiosum (fifth disease), characterized by a "slapped cheek" rash and a lacy reticular exanthem on the extremities. It does not typically present with high fever preceding the rash.

• (C) Measles virus: Causes measles, which presents with Koplik spots in the mouth followed by a maculopapular rash that starts on the face and spreads downward, accompanied by high fever and cough. The rash appears during the fever, not after it resolves.

• (D) Group A Streptococcus: Causes scarlet fever, which presents with a sandpaper-like rash, strawberry tongue, and pharyngitis during the febrile illness.

• (E) Coxsackievirus A16: Causes hand, foot, and mouth disease, characterized by vesicles/ulcers in the mouth and on the palms/soles, with a mild fever.

Management:

• Supportive care: Antipyretics (e.g., acetaminophen) for fever and hydration.

• No specific antiviral treatment is needed for immunocompetent children.

Complications:

• Febrile seizures are the most common complication due to rapid rise in fever.

• Rarely, hepatitis or encephalitis may occur.

Prognosis:
Excellent; full recovery is expected. Immunity is lifelong after primary infection.