Human Metapneumovirus: An Overview

 

 

*Tamanna Singh

*Senior Resident , Department of Medicine Lady Hardinge Medical College

Introduction

Human metapneumovirus (HMPV) is a respiratory virus first discovered in 2001 in the Netherlands [1]. Retrospective studies suggest that HMPV has been present in human populations for decades, with evidence tracing its existence back to the 1950s [7]. This virus primarily impacts young children, older adults, and individuals with weakened immune systems [6]. This article explores HMPV, covering its virology, epidemiology, clinical features, diagnostic methods, treatment options, and recent developments.

Virology

HMPV is a member of the Paramyxoviridae family and Pneumovirinae subfamily, closely related to respiratory syncytial virus (RSV) [1, 7]. It is an enveloped, single-stranded RNA virus with a negative-sense genome approximately 13 kilobases in length [15]. The genome encodes nine proteins, including:

  • Fusion (F) protein: Enables viral entry by facilitating membrane fusion [17].
  • Attachment (G) protein: Aids in the initial binding to host cells [17].
  • Nucleoprotein (N), Phosphoprotein (P), and Large polymerase (L): Play essential roles in RNA replication and transcription [7].
  • Matrix (M) protein: Involved in virus assembly [15].

HMPV is categorized into two major genetic lineages, A and B, which are further divided into subgroups A1, A2, B1, and B2 [13]. These genetic variations influence antigenic properties but do not significantly impact the severity of illness [13, 18].

Epidemiology

HMPV is distributed globally and has been detected on all continents [6]. In regions with temperate climates, HMPV typically circulates in late winter and spring, often overlapping with or following the seasonal activity of RSV [5].

 Prevalence

  • HMPV is a leading cause of lower respiratory tract infections (LRTIs) in children under five, second only to RSV [5, 12].
  • Studies show that most children have been exposed to HMPV by the age of five [6, 8].
  • Adults, especially those with chronic health issues, are also susceptible to reinfection, often presenting with mild upper respiratory symptoms [6].

Transmission

HMPV spreads through close contact with infected individuals or contaminated surfaces [8, 10]. Transmission methods include:

  • Respiratory droplets from coughing or sneezing.
  • Direct contact, such as caregiving or handshakes.
  • Touching contaminated surfaces and then touching the mouth, nose, or eyes [8].

The virus can survive on surfaces for several hours, making it highly transmissible [6]. Contagion is highest during the early stages of illness [6, 10].

Clinical Manifestations

The clinical presentation of HMPV ranges from asymptomatic infection to severe respiratory illness, depending on factors such as age, immune status, and underlying health conditions [9].

Symptoms

  • Mild cases: Runny nose, cough, low-grade fever, and sore throat [6, 9].
  • Moderate to severe cases: Wheezing, difficulty breathing, and low oxygen levels, which may require hospitalization [9].

Complications

  • Bronchiolitis and pneumonia: Frequently seen in infants and young children [5, 9].
  • Worsening of chronic respiratory conditions: Such as asthma and chronic obstructive pulmonary disease (COPD) [6, 9].
  • Secondary bacterial infections: Including ear infections and bacterial pneumonia [9, 12].

Diagnosis

Laboratory Tests

  • RT-PCR (Reverse Transcription Polymerase Chain Reaction): Detects viral RNA and is a reliable diagnostic tool [16].
  • ELISA (Enzyme-Linked Immunosorbent Assay): Identifies antibodies or viral antigens in patient samples [16].
  • Nucleic Acid Amplification Tests (NAAT): Highly sensitive for detecting the viral genome [16].
  • Immunofluorescence or Enzyme Immunoassays: Confirm the presence of viral antigens [16].

Additional Testing

In severe cases requiring hospitalization, bronchoscopy may be performed to collect lung fluid samples for further analysis [16].

Treatment

There are no specific antiviral treatments approved for HMPV. Care focuses on alleviating symptoms [18].

Mild Cases

  • Use of antipyretics, hydration, and rest to manage symptoms [6].

Severe Cases

  • Oxygen therapy for low oxygen levels [6].
  • Mechanical ventilation in cases of respiratory failure [6].
  • Nebulized bronchodilators and corticosteroids may be used, though their effectiveness is uncertain [9, 18].

Experimental therapies, including monoclonal antibodies and small-molecule inhibitors targeting the F protein, are under investigation [17].

Prevention

To minimize the risk of HMPV infection and other respiratory illnesses [6]:

  • Wash hands frequently with soap and water or use hand sanitizer.
  • Cover your mouth and nose with your elbow when coughing or sneezing.
  • Avoid close contact with individuals who are sick.
  • Wear a mask if you are ill and cannot avoid contact with others.
  • Refrain from touching your face, particularly the eyes, nose, and mouth.
  • Do not share food or utensils with others.

Recent Developments and Public Health Implications

In late 2024 and early 2025, an increase in HMPV cases in China raised concerns about a potential new pandemic [2]. However, health organizations, including the World Health Organization (WHO), clarified that the rise aligns with seasonal trends and does not pose a threat comparable to COVID-19 [2]. Experts highlight that while HMPV can cause severe illness in vulnerable groups, it is a well-understood virus with predictable seasonal patterns [2, 13]. Standard preventive measures remain effective [6].

Conclusion

HMPV is a significant cause of viral respiratory infections, particularly affecting vulnerable populations such as older adults, immunocompromised individuals, and those with underlying health conditions [6]. Although it shares similarities with RSV, ongoing research aims to uncover its unique characteristics to inform the development of targeted treatments and vaccines [17]. Raising public awareness and adhering to preventive strategies are crucial for mitigating the impact of HMPV, especially during its peak seasons [6]

 

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