Human parainfluenza viruses are important respiratory pathogens in children and adults. In infants and young children, parainfluenza viruses are the most common cause of lower respiratory tract infections after respiratory syncytial virus (RSV) [1-3]. Lower respiratory infections (eg, bronchiolitis, interstitial pneumonitis, pneumonia) are a leading cause of morbidity and mortality in infants during the first year of life in the United States and in children younger than the age of six years in developing countries . In adults, parainfluenza viruses generally cause mild upper respiratory infections (URIs) but can induce more severe disease in the elderly. Immunocompromised patients, particularly lung and hematopoietic cell transplant recipients can experience life-threatening lower respiratory tract infections with parainfluenza virus [4,5].
The virology, clinical manifestations, diagnosis, and treatment of parainfluenza viruses in children will be reviewed here. Infection with parainfluenza viruses in adults is discussed separately. (See "Parainfluenza viruses in adults".)
Virus — Parainfluenza viruses (PIV) are single-stranded, enveloped RNA viruses belonging to the genus paramyxovirus in the Paramyxoviridae family . This family also includes human mumps, measles, and respiratory syncytial viruses and metapneumoviruses, as well as avian, bovine, and murine strains of these viruses.
The virions are pleomorphic and range in diameter from 150 to 200 nm. The single strand of negative-sense RNA is 15,462 nucleotides in length and encodes six common viral proteins: the nucleocapsid protein (NP), the phosphoprotein (P), the matrix protein (M), the fusion glycoprotein (F), the hemagglutinin-neuramininidase glycoprotein (HN), and the RNA polymerase (L) .
- The HN and F proteins project through the lipid envelope and form the major antigenic targets for neutralizing antibody . Their hydrophobic tails project into the virion, where they interact with the M protein to aid in virus assembly .
- The nucleocapsid core is composed of NP, P, and L proteins in association with viral RNA. NP proteins bind tightly to the viral genome, creating a template for the RNA-dependent RNA polymerase composed of the P and L proteins .