Human Metapneumovirus (hMPV) Pneumonia

Human metapneumovirus (hMPV) is an enveloped, negative-sense single-stranded RNA virus belonging to family Paramyxoviridae, subfamily Pneumovirinae, genus Metapneumovirus, first identified in 2001 by van den Hoogen in the Netherlands. Two main genetic groups (A and B) with sublineages A1, A2, B1, B2 circulate globally, with seasonal peaks in late winter and early spring (similar to influenza but later). Most children are seropositive by age 5, indicating widespread early-life infection.

Transmission is via respiratory droplets, contact with contaminated surfaces, and aerosols, with incubation 4-6 days. hMPV accounts for 5-15% of acute respiratory tract infections in hospitalized children, second only to RSV among viral causes of bronchiolitis and pneumonia in young children. High-risk populations include children <5 years (peak in 6-12 months), elderly >65 years, immunocompromised hosts (hematopoietic cell transplant recipients with mortality 27-43%, lung transplant recipients with risk of bronchiolitis obliterans), and those with chronic lung diseases (COPD, asthma) where hMPV is a major cause of exacerbations.

Clinical presentation includes cough, fever, rhinorrhea, sore throat, wheezing, dyspnea, and hypoxia in severe cases. Disease spectrum ranges from upper respiratory tract infection (most common) to bronchiolitis (similar to RSV), pneumonia, and ARDS in severe cases. Diagnosis is established by reverse transcription PCR (RT-PCR) on nasopharyngeal swab, often included in multiplex respiratory virus panels alongside RSV, influenza, parainfluenza, adenovirus, rhinovirus, and SARS-CoV-2. Imaging shows ground-glass opacities, peribronchial thickening, and patchy consolidations. No specific antiviral therapy has FDA approval; ribavirin and IVIG used off-label in severe immunocompromised disease.