Dermatology MCQ - Viral Infections - Measles

A 4-year-old unvaccinated child presents with high fever, cough, coryza, conjunctivitis, and bluish-white slightly raised spots on an erythematous base on the buccal mucosa. On day 3 of illness, a maculopapular rash appears on the face and spreads downward. Which of the following is the most likely causative agent and its primary mode of transmission?

A) Rubella virus; respiratory droplets
B) Measles virus; airborne transmission
C) Human herpesvirus 6; respiratory secretions
D) Parvovirus B19; respiratory droplets
E) Enterovirus; fecal-oral route

Correct Answer: B) Measles virus; airborne transmission

Explanation

This presentation is classic for measles (rubeola), a highly contagious viral illness.

Key Clinical Features of Measles:

• Prodrome (2-4 days): High fever, cough, coryza (runny nose), conjunctivitis ("the 3 C's").

• Koplik spots: Pathognomonic enanthem — small, white, bluish-centered spots on the buccal mucosa opposite the molars.

• Rash: Erythematous maculopapular rash that begins on the face (hairline/behind ears) and spreads cephalocaudally to trunk and extremities. The rash may become confluent.

• Other symptoms: Photophobia, malaise, anorexia.

Virologic and Transmission Features:

• Causative Agent: Measles virus (a paramyxovirus).

• Transmission:

  • Airborne transmission via respiratory droplets (highly contagious, R0 ~12-18).

  • Virus remains infectious in air for up to 2 hours.

• At-risk populations: Unvaccinated children, immunocompromised individuals.

Why Not the Other Options?

• (A) Rubella virus: Causes German measles with a similar rash but milder symptoms (no Koplik spots, no severe cough/coryza). Rash starts on face but spreads quickly.

• (C) Human herpesvirus 6: Causes roseola infantum (high fever for 3-5 days followed by rash after fever resolves). No Koplik spots or prominent respiratory symptoms.

• (D) Parvovirus B19: Causes erythema infectiosum ("slapped cheek" rash) and lace-like rash on extremities. No Koplik spots or prodromal respiratory symptoms.

• (E) Enterovirus: Causes hand, foot, and mouth disease (vesicles on hands/feet/mouth) or herpangina (posterior pharyngeal vesicles), not a maculopapular rash with Koplik spots.

Complications:

• Pneumonia, encephalitis, subacute sclerosing panencephalitis (SSPE) years later.

Management:

• Supportive care: Hydration, antipyretics, vitamin A (reduces morbidity/mortality).

• Isolation: Airborne precautions.

• Post-exposure prophylaxis: MMR vaccine within 72 hours or immune globulin within 6 days.

Prevention:

• MMR vaccine (live attenuated) at 12-15 months and 4-6 years.

Prognosis:
Most recover, but measles causes significant mortality in malnourished or unvaccinated children.

Note: The description of Koplik spots + cough/coryza/conjunctivitis + cephalocaudal rash is diagnostic for measles. Always consider measles in unvaccinated children with febrile rash illness.