Definition
• Lung infection caused by an RNA virus in the Paramyxovirus family closely related to avian pneumovirus
Clinical features
Epidemiology
• Isolated first in The Netherlands in 2001; data suggest that this is a common virus responsible for respiratory illnesses for at least 50 years
• Seen in all age groups: major cause of bronchiolitis and croup predominantly in the first year of life
• Initial seroprevalence data document that all children are positive by the age of 5
• Responsible for >2% to 3% of respiratory tract infections in community surveillance studies including children and adults
• Prevalence in children with lower respiratory tract infection is approximately 12%
• Can be associated with clinically important reinfection in late childhood or adult life
• Often cocirculates with influenza and respiratory syncytial virus (RSV); therefore, it can lead to clinical diagnostic confusion
• Associated with community-acquired pneumonia in the late winter and early spring
Presentation
• Symptoms are similar to RSV infection and range from mild respiratory illness to respiratory failure requiring ventilation
• Usually a self-limited and mild acute upper respiratory tract infection with symptoms including runny nose, nasal congestion, sore throat, fever, malaise, lethargy, coughing
• Severe disease, often seen in children younger than 1 year, immunocompromised patients, and elderly patients, may present with high fever, severe cough, difficulty breathing, wheezing, vomiting, diarrhea
Prognosis and treatment
• Mild cases: no therapy or symptomatic therapy
• Severe cases: breathing treatments
Pathology
Histology
• Pulmonary congestion with edema can be noted
• Interstitial inflammatory cell infiltration ranges from minimal to severe
• Atypical multinucleated pneumocytes and atypical bronchiolar epithelial cells can be observed
• Definite viral inclusions are not identified
• In severe infections, especially in transplantation patients, the lung demonstrates diffuse alveolar damage as well as distended bronchioles and alveolar ducts lined by hyaline membranes
Immunopathology/special stains
• Testing is not widely available
• Polymerase chain reaction is performed at some research institutions and some commercial laboratories
Main differential diagnoses
• RSV, influenza virus, parainfluenza virus