Overview

Human parainfluenza viruses (HPIVs) are among the most common causes of respiratory tract infection, especially in young children. HPIV is a member of the Paramyxoviridae family of viruses with an RNA genome enclosed in a capsid surrounded by a lipid envelope. Much of the pathology caused by HPIV is related to damage of the lining of the small airways of the respiratory tract. HPIV is a common virus infection that often resembles the common cold with mild symptoms such as a runny nose, coughing and low-grade fever; however, HPIV can cause more severe diseases such as bronchiolitis and pneumonia in young children. Those at greatest risk of severe infection include premature infants and children with heart or lung disease.

There are four types of HPIV (HPIV-1, HPIV-2, HPIV-3 and HPIV-4). Although all four types of HPIV cause disease, most significant infections are caused by HPIV-1 and HPIV-3, whereas HPIV-4 is the least common cause of disease. HPIV-1 is the major cause of the syndrome referred to as croup, which is laryngotracheitis that causes a characteristic bark-like cough, infecting mostly infants and young children. HPIV infections can occur any time of year, but most infections occur from October through April.