Human parainfluenza viruses cause croup, pneumonia, bron-chiolitis and tracheobronchitis, and some other infections.
Croup or laryngotracheobronchitis is a heterogeneous group of illnesses that affects the larynx, trachea, and bronchi. The condition manifests as fever, cough, laryngeal obstruction, and expiratory stridor. HPIV-1, HPIV-2, and HPIV-3 are the com-mon causes of croup; of which HPIV-1 is the most common.
HPIV-1 and HPIV-3 are responsible for most cases of human parainfluenza pneumonia. Fever, rales, and evidence of pulmo-nary consolidation are the common symptoms.
Bronchiolitis is caused by all the five types of HPIV, but HPIV-1 and HPIV-3 are the most common causes. Most cases of bronchi-olitis occur in infants. The condition manifests as fever, expira-tory wheezing, tachypnea, and rales. HPIV-3 is more commonly associated with tracheobronchitis than HPIV-1 or HPIV-2.
Otitis media, pharyngitis, conjunctivitis, and coryza are the other infections caused by HPIV.
Human parainfluenza viruses are ubiquitous.
HPIVs (HPIV-1, HPIV-2, HPIV-3, and HPIV-4) have worldwide distribution. HPIV-1 is usually associated with epidemics of the disease.
Parainfluenza viruses cause disease exclusively in humans. No animal reservoirs are present. Respiratory secretions from the infected humans are the source of infection. The infection is transmitted by inhalation of respiratory droplets or by direct person-to-person contact with infected secretions.