- Pathogenesis of Acute Bronchiolitis.

Pathogenesis of Acute Bronchiolitis. 

RSV initially multiplies in the epithelium of the nasopharynx.
It then forms a syncytium and invades nearby cells.
 Hence, progression within few days of illness from an upper respiratory infection to a lower respiratory tract involvement is from cell to cell rather than hematogenous, extra-cellular fluid or any other route.
 The virus mainly multiplies within the bronchial epithelium and the alveolar macrophages.

 It finally results in:
o Destruction of the bronchiolar lining epithelium and loss of ciliated epithelial cells.
o Peribronchial infiltration of white blood cells.
o oedema of the submucosa and adventitia.
o ↑ Secretion
o Plugs of sloughed, necrotic epithelium and fibrin in the airways cause significant small airway obstruction (bronchospasm) resulting in hyperinflation, obstructive emphysema, atelectasis and ventilation/perfusion mismatch leading to hypoxemia.

N.b: Bronchial muscles are spared in bronchiolitis.