Viruses: Life Cycle and Disease · USMLE Step 1

An infant with laryngotracheobronchitis (croup) presents with a barking cough and inspiratory stridor. Which virus is the most likely cause?

  1. Respiratory syncytial virus
  2. Parainfluenza virus
  3. Rhinovirus
  4. Adenovirus
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Correct answer: Parainfluenza virus

Parainfluenza virus, a paramyxovirus, is the classic cause of croup. It leads to subglottic swelling and the characteristic barking cough.

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