The viral infection that causes<unk>  leads to swelling of the larynx, trachea, and large bronchi due to infiltration of white blood cells (especially histiocytes, lymphocytes, plasma cells, and neutrophils). Swelling produces airway obstruction which, when significant, leads to dramatically increased work of breathing and the characteristic turbulent, noisy airflow known as stridor.
Croup
Foreign body
Bronchorrhea
Epiglottitis
Tonsillitis
Tracheitis
Laryngitis
Post-nasal drip