Human parainfluenza viruses are enveloped, helical, single stranded RNA (-) viruses with diameters of 150 to 250 nm. There are four types of parainfluenza virus, all of which can cause respiratory infections.
The exact number of parainfluenza cases is unknown. The number is suspected to be very high. Sometimes the viruses cause only a runny nose and other symptoms that may be diagnosed as a simple cold.
Clinical features: Parainfluenza virus serotypes 1, 2 and 3 cause laringotracheobronchitis (croup) in children between two and four years of age. Serotype 3 is the second agent producing pneumonia in children less than one year old (after respiratory syncytial virus) and it also has an epidemic pattern.
Infections are most common in fall and winter. Parainfluenza infections are most severe in infants and become less severe with age. By school age, most children have been exposed to the parainfluenza virus. Most adults have antibodies against parainfluenza, although they can get repeat infections.
Symptoms vary depending on the type of infection. Cold-like symptoms consisting of a runny nose and mild cough are common. Life-threatening respiratory symptoms can be seen in young infants with bronchiolitis and those with weakened immune systems.
Diagnosis: PIV infection can be diagnosed in the laboratory by direct methods (antigen direct detection in clinical samples, culture techniques or nucleic acid tests) or by serological tests to measure the presence of IgM or the increase of IgG titers. The monkey LLC‐MK2 cell line is used in many laboratories for the culture of PIV.
Treatment: Most infections in adults and older children are mild and recovery takes place without treatment, unless the person is very old or has an abnormal immune system. There is no specific treatment for the viral infection; however, specific treatments are available for the symptoms of croup and bronchiolitis in order to make breathing easier.