Ans. B. Parainfluenza
This child initially had fever, rhinitis, and pharyngitis, which are symptoms typical of an upper respiratory tract infection (URI}. When a child with a history of recent URI develops a brassy, barking cough and breathing difficulties, it is likely – that acute laryngotracheitis (croup) has developed. The dyspnea associated with croup occurs when inflamed subglottic tissue obstructs the upper airway. The characteristic stridor of the croup is a sign of significant upper airway obstruction. Croup is typically caused by the standard URI viruses, with the parainfluenza viruses (members of Paramyxoviridae) most commonly responsible.