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Human Metapneumovirus: A New Threat in the Post-Pandemic Era

M3 India Newsdesk Jan 14, 2025

Human Metapneumovirus is a respiratory pathogen of significant clinical concern, particularly in children, the elderly, and immunocompromised individuals. As respiratory viruses remain a pressing health concern, it is vital to explore the current clinical impact and scientific understanding of hMPV.


First identified in 2001, this virus has gained attention for its global prevalence and its role in causing respiratory illnesses ranging from mild upper respiratory infections to severe bronchiolitis and pneumonia. As respiratory viruses remain a pressing health concern, it is vital to explore the current epidemiology, clinical impact, and scientific understanding of hMPV.


Virology

  1. Human Metapneumovirus (hMPV) was first discovered in 2001 in the Netherlands when the virus was isolated from a paediatric patient who had symptoms similar to those of human Respiratory syncytial virus (hRSV).
  2. Pneumovirinae and Paramyxovirinae are subfamilies of the Paramyxoviridae family, which is a member of the order Mononegavirales.
  3. Pneumovirus and Metapneumovirus are the two genera that make up the Pneumovirinae subfamily. 
  4. hMPV belongs to the genus Metapneumovirus, whereas hRSV is classified under the genus Pneumovirus.
  5. It is an enveloped, negative-sense, single-stranded RNA virus with two major subgroups: A and B, further divided into genetic lineages A1, A2, B1, and B2.
  6. Since its discovery in the Netherlands, hMPV has been identified worldwide as a leading cause of respiratory infections.

Pathogenesis

Human metapneumovirus (hMPV) infects the respiratory epithelium, initiating replication and triggering an immune response. The infection often leads to inflammation in the lower respiratory tract, with significant effects seen in alveoli and bronchioles. The virus induces a Th17-like immune response, characterised by increased levels of cytokines such as IL-6 and TNF-α, which contribute to neutrophil recruitment and mucus hypersecretion. These changes can result in airway obstruction and alveolar collapse.

Additionally, hMPV manipulates the host immune system, promoting an ineffective Th2 response and inhibiting critical signalling pathways like interferon (IFN) responses via its G and SH proteins. This immune evasion leads to delayed viral clearance. Persistent inflammation and structural changes in the lungs, including increased thickness of alveolar walls and peri bronchiolitis, are hallmarks of severe cases.


Clinical manifestations

hMPV infections can affect individuals of all ages but are most severe in:

  1. Children: It is a leading cause of bronchiolitis, pneumonia, and croup in children under five. Symptoms include fever, cough, wheezing, and respiratory distress.
  2. Elderly adults: Older adults, especially those with underlying conditions like chronic obstructive pulmonary disease (COPD) or heart failure, may experience exacerbations or severe lower respiratory tract infections.
  3. Immunocompromised patients: This population faces a higher risk of severe outcomes, including prolonged viral shedding and complications such as acute respiratory failure.

Present spread and epidemiological insights

The global spread of hMPV is well-documented, with outbreaks reported across continents. Surveillance data from North America, Europe, and Asia indicate hMPV’s consistent contribution to respiratory illnesses. Recent studies have highlighted:

  1. Increased detection post-COVID-19: The COVID-19 pandemic disrupted the typical seasonal circulation of many respiratory viruses. As pandemic-related restrictions eased, a surge in hMPV cases was observed, particularly in children who had reduced viral exposure during lockdowns.
  2. Co-infections and syndemics: hMPV often co-circulates with RSV, influenza, and SARS-CoV-2, leading to co-infections that exacerbate disease severity. Studies have shown that dual infections with hMPV and other respiratory pathogens increase the risk of hospitalization and intensive care admission.
  3. Regional variability: While hMPV is ubiquitous, its prevalence and seasonal peaks can vary geographically. In tropical regions, for instance, the virus may circulate year-round, contrasting with the seasonal peaks seen in temperate climates.

Advances in diagnostic methods

Accurate and timely diagnosis of hMPV is critical for patient management and outbreak control. Conventional diagnostic methods include:

  1. Molecular testing: Reverse transcription polymerase chain reaction (RT-PCR) is the gold standard for hMPV detection due to its high sensitivity and specificity.
  2. Antigen detection: Rapid antigen tests are less sensitive but useful in resource-limited settings.
  3. Serological tests: Though not commonly used for acute diagnosis, serology can help in epidemiological studies.

The development of multiplex PCR assays capable of detecting hMPV alongside other respiratory viruses has enhanced diagnostic capabilities, particularly during peak respiratory illness seasons.


Treatment and management

Currently, no specific antiviral therapy or vaccine is available for hMPV. Management is primarily supportive, including:

  1. Oxygen therapy for hypoxemia.
  2. Bronchodilators and corticosteroids for wheezing or airway inflammation, though their efficacy remains debated.
  3. Mechanical ventilation in severe cases.

The absence of targeted treatments underscores the need for preventive measures such as hand hygiene, respiratory etiquette, and isolation of infected individuals in healthcare and community settings.


Prevention

Preventive measures are similar to those that were followed during the COVID-19 pandemic. It includes:

  1. Washing hands frequently with soap and water for at least 20 seconds.
  2. Avoid touching the eyes, nose, or mouth with unwashed hands.
  3. Avoid close contact with people who are sick.
  4. Covering the mouth and nose when coughing or sneezing, use of masks.
  5. Cleaning frequently touched surfaces.
  6. Staying at home when sick.
  7. Improve indoor air quality: Use air purifiers and ensure good ventilation in living and working spaces.
  8. Boost immunity.
  9. Vaccination research: While no vaccine is currently available for hMPV, staying updated on developments and participating in vaccination programs when available is crucial.
  10. Awareness and education.

Public health implications

India has reported seven cases of Human Metapneumovirus (hMPV) infections in children, with cases being confirmed in Bengaluru, Nagpur, Tamil Nadu, and Ahmedabad. China took a backseat over the concern of rising HMPV cases in the country and called it an “annual seasonal reoccurrence”. While confirming the surge in cases, a Chinese foreign ministry official blamed it on the “winter season”.

 

Disclaimer- The views and opinions expressed in this article are those of the author and do not necessarily reflect the official policy or position of M3 India.

About the author of this article: Dr Priya Sharma is a Consultant Pulmonologist at Indraprastha Apollo Hospitals, Delhi.

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