Lung bronchioles and alveoli in bronchiolitis, illustration. Bronchiolitis is the inflammation and blockage of the bronchioles (small lung airways) due to a viral infection. Mucus forms and blocks the bronchioles and alveoli, which can severely reduce lung capacity. This disease can result in mucus plugs, airway wall remodelling, oedema of lung airways, hypertrophied bronchial muscles, and acute constriction of the bronchioles.