Human Metapneumovirus (HMPV): An Overview

Human Metapneumovirus (HMPV) is the first human member of the Metapneumovirus genus, and it belongs to the Paramyxoviridae family. It is an enveloped, single-stranded RNA virus known to cause respiratory infections in humans.

Phylogenetic analyses have revealed two major genotypes, Group A and Group B, which are further divided into lineages like A2.2.1 and A2.2.2. These classifications are based on genetic variability, particularly in the sequences of the fusion (F) and attachment (G) glycoproteins. While global research has tracked changes in these lineages, there is still a lack of data on their frequency and genetic diversity in specific regions, including parts of India. Understanding this diversity is crucial for monitoring viral evolution and potential outbreaks.

Transmission and High-Risk Groups

HMPV infections can occur in individuals of all age groups. However, young children, the elderly, and immunocompromised individuals are at higher risk of severe disease. Animal studies have shown that aged mice exhibit higher susceptibility and delayed viral clearance compared to younger mice, suggesting that age-related immune decline plays a role in disease severity.

The virus is transmitted primarily through direct or close contact with infected respiratory secretions, such as saliva or droplets.

Clinical Presentation

HMPV’s symptoms are similar to those of other respiratory viruses, such as RSV or influenza, making diagnosis difficult. Some of the most common symptoms are:

• Fever
• Cough
• Nasal congestion
• Sore throat
• Dyspnea (shortness of breath)

In severe cases, especially among high-risk populations, HMPV can cause hospitalization due to complications such as:

• Pneumonia
• Bronchiolitis
• Exacerbation of chronic illnesses (e.g., asthma, COPD)
• Secondary bacterial infections
• Pregnancy-related complications

Most patients recover within 7–10 days; however, vulnerable groups are at a higher risk of prolonged or severe illness.

Recent Outbreaks and Seasonality

A large outbreak of HMPV in China recently drew international attention due to its rapid spread and impact on young children and the elderly.
The investigation of this outbreak revealed a distinct seasonal pattern, with infections peaking during winter and early spring, particularly in December and January, as with other respiratory viruses.

Challenges in Diagnosis

One of the primary challenges in controlling HMPV is misdiagnosis. Because its symptoms overlap with those of other respiratory infections, laboratory testing is essential for accurate diagnosis.

Diagnostic tools include:

• Polymerase Chain Reaction (PCR) for viral RNA detection
• Antigen detection tests for rapid identification
  

Early and accurate diagnosis is crucial for effective management and monitoring outbreaks.

Pathogenesis and Immune Response

The persistence of HMPV infection is largely due to a delayed immune response and impaired cytotoxic T-cell activity during primary infection. The virus interferes with cytokine signaling, disrupting T-cell activation and proliferation.

HMPV has eight genes encoding nine proteins, which play distinct roles in the viral life cycle and pathogenicity.

• The glycoprotein (G) facilitates viral attachment to the host cell.
• The fusion protein (F) binds to host cell integrins, allowing viral entry.

This interaction causes the release of pro-inflammatory cytokines, including IL-6, TNF-α, and IL-2, as well as the recruitment of inflammatory cells, especially around vascular tissues. These immune responses cause pulmonary inflammation, which results in respiratory symptoms such as fever, cough, mucus production, and dyspnea.

Current Management and Therapeutic Approaches

Currently, there are no approved antiviral treatments or vaccines for HMPV. Management is primarily focused on symptomatic relief and supportive care, which can include:

• Hydration and rest
• Oxygen therapy for severe cases
• Bronchodilators or corticosteroids for patients with chronic lung conditions
• Monitoring and management of secondary bacterial infections

The development of effective antivirals and vaccines remains a critical research priority to reduce the global burden of HMPV.

Conclusion

HMPV is a major but often overlooked cause of respiratory illness worldwide. Its genetic diversity, diagnostic challenges, and lack of specific treatment options make it a public health concern, especially among vulnerable populations. Continuous research and surveillance are required to better understand the epidemiology, improve diagnostic capabilities, and develop targeted interventions such as vaccines and therapeutics.

References:

• Haas, L. E., Thijsen, S. F., van Elden, L., & Heemstra, K. A. (2013). Human metapneumovirus in adults. Viruses, 5(1), 87–110. https://doi.org/10.3390/v5010087

• https://bigapollospectra.com/blog/major-causes-of-lung-failure-examining-the-causes/

• Panda, S., Mohakud, N. K., Pena, L., & Kumar, S. (2014). Human metapneumovirus: review of an important respiratory pathogen. International journal of infectious diseases : IJID : official publication of the International Society for Infectious Diseases, 25, 45–52. https://doi.org/10.1016/j.ijid.2014.03.1394

• https://my.clevelandclinic.org/health/diseases/22443-human-metapneumovirus-hmpv

• https://euracare.com.gh/respiratory-medicine/

About the Author

Brahmi Shenoy

Editor

View All Posts