PARAINFLUENZA DISEASE : CLINICAL ASPECTS
The onset of illness may be abrupt, as in acute spasmodic croup, but usually begins as a mild URI with variable progression over 1 to 3 days to involvement of the middle or lower respi-ratory tract. Duration of acute illness can vary from 4 to 21 days but is usually 7 to 10 days.
Parainfluenza 1 is the major cause of acute croup (laryngotracheitis) in infants and young children but also causes less severe diseases such as mild upper respiratory illness (URI), pharyngitis, and tracheobronchitis in individuals of all ages. Outbreaks of infection tend to occur most frequently during the fall months.
Parainfluenza 2 is of slightly less significance than parainfluenza 1 or 3. It has been associated with croup, primarily in children, with mild URI, and occasionally with acute lower respiratory disease. As with parainfluenza 1, outbreaks usually occur during the fall months.
Parainfluenza 3 is a major cause of severe lower respiratory disease in infants and young
children. It often causes bronchitis, pneumonia, and croup in children less than 1 year of age. In older children and adults, it may cause URI or tracheobronchitis. Infections are common and can occur in any season; it is estimated that nearly one half of all children have been exposed to this virus by 1 year of age.
Parainfluenza 4 is the least common of the group. It is generally associated with mild up- per respiratory illness only.
Specific diagnosis is based on virus isolation, usually in monkey kidney cell cultures, or on serology using hemagglutination inhibition, complement fixation, or neutralization as-says on paired sera to detect a rising antibody titer. Immunofluorescence or immunoen-zyme assays can also be used for rapid detection of antigen in respiratory epithelial cells. Currently, there is no method of control or specific therapy for these infections.