Human Metapneumovirus (HMPV): An Overview
Human metapneumovirus (HMPV or hMPV) is a negative-sense, single-stranded RNA virus from the Pneumoviridae family. Closely related to avian metapneumovirus (AMPV) subtype C, it was first discovered in 2001 using RNA arbitrarily primed PCR (RAP-PCR) in the Netherlands. It primarily targets the respiratory system and is a significant cause of respiratory infections worldwide.
Recent Outbreaks (2024-2025)
A significant outbreak of HMPV began in late 2024, with the Chinese Center for Disease Control and Prevention reporting rising cases. During December 2024, HMPV accounted for 6.2% of respiratory illness tests and 5.4% of hospitalizations in China, surpassing other viruses like COVID-19, rhinovirus, and adenovirus.
As of 2025, cases have also been reported in Malaysia, Hong Kong, and India, highlighting its growing impact in Asia.
Discovery and Naming
HMPV was first identified in the respiratory secretions of 28 children in the Netherlands. Initial diagnostic methods, including immunological assays and PCR-based techniques, failed to identify the virus as it was unknown at the time. Molecular biology techniques, such as randomly primed PCR, later revealed genetic similarities between HMPV and AMPV, classifying it as human metapneumovirus.
What is the Epidemiology of HMPV?
HMPV is globally distributed and exhibits seasonal patterns, primarily occurring in late winter and spring in temperate regions.
Key epidemiological data include:
- HMPV causes 12% of acute respiratory tract illnesses in children under five in outpatient settings.
- It accounts for 15% of community-acquired pneumonia hospitalizations in children under five and 8% over five.
- Reinfections are common despite nearly universal exposure by the age of five.
- Vulnerable populations include premature infants, immunocompromised individuals, older adults over 65, and people with asthma or chronic obstructive pulmonary disease (COPD).
How is HMPV Virus transmitted?
HMPV spreads through multiple transmission routes:
- Respiratory droplets from coughing or sneezing.
- Close personal contact, such as touching or shaking hands.
- Contact with contaminated surfaces, followed by touching the mouth, nose, or eyes.
What are the Symptoms of HMPV?
HMPV infections can range from mild to severe. Common symptoms include:
- Runny nose and cough.
- Fever and fatigue.
- Wheezing or difficulty breathing in severe cases, particularly in high-risk groups.
Genome and Virology of HMPV
The HMPV genome is a negative-sense RNA that lacks non-structural genes NS1 and NS2, with eight open reading frames arranged differently from RSV. Phylogenetic studies identify two genetic lineages, A and B, further divided into subgroups A1, A2, B1, and B2. Infection begins with attachment to respiratory epithelial cells via the G protein, followed by membrane fusion mediated by the F protein.
HMPV infects airway epithelial cells and induces chemokine and cytokine responses, such as IL-6 and TNF-alpha, leading to inflammation in the respiratory tract.
Detection and Diagnosis of HMPV
HMPV is diagnosed using several methods:
- RT-PCR: The most reliable method for detecting HMPV RNA in respiratory samples.
- Immunofluorescence: Antigen detection and antibody-based testing for viral identification.
- Cell Culture: Direct virus isolation in cultured cells, though less commonly used.
What are the Current Treatment Options?
No specific treatment exists for HMPV. Management focuses on supportive care, such as hydration and oxygen therapy. Experimental approaches include:
- Ribavirin: Shown effective in animal models.
- Vaccines: Moderna’s modRNA vaccine candidate has passed Phase I clinical trials, demonstrating immune response and safety.
Conclusion
HMPV is a globally prevalent respiratory virus, especially dangerous to young children, older adults, and immunocompromised individuals. While supportive care remains the primary treatment, ongoing vaccine trials and antiviral research offer hope for better prevention and management of this infectious disease.
