Human Metapneumovirus: How it’s affecting Children and Adults Differently

Human Metapneumovirus (hMPV) is a respiratory pathogen that has garnered increased attention due to recent outbreaks, particularly in regions like northern China. While it affects individuals across all age groups, the virus manifests differently in children and adults, leading to varied clinical outcomes.
Understanding Human Metapneumovirus (hMPV)
First identified in 2001, hMPV belongs to the Pneumoviridae family, closely related to the Respiratory Syncytial Virus (RSV). It is a leading cause of respiratory infections worldwide, especially during the winter and spring months. The virus spreads through respiratory droplets, direct contact with contaminated surfaces, or close personal contact.

How hMPV Affects Children

Severe Respiratory Symptoms
In children, especially those under five, hMPV can cause:
• Bronchiolitis: Inflammation of the small airways in the lungs.
• Pneumonia: Severe lung infections requiring hospitalization.
• Croup: A barking cough caused by airway inflammation.

Vulnerable Groups
• Premature Infants: They often have weaker lungs, making them more susceptible.
• Immunocompromised Children: Those with underlying conditions face prolonged and severe illnesses.

Higher Rates of Hospitalization
Children infected with hMPV often require hospitalization due to respiratory distress, particularly during flu season, when the virus spreads more easily.

How hMPV Affects Adults
Milder Symptoms in Healthy Adults
For most healthy adults, hMPV symptoms mimic a common cold:
• Runny nose
• Cough
• Sore throat
• Low-grade fever

Severe Cases in Older Adults
Older adults, especially those over 65 or with underlying conditions like chronic obstructive pulmonary disease (COPD), face more significant risks, including:
• Exacerbation of existing respiratory conditions.
• Severe pneumonia.
• Increased hospitalizations during outbreaks.

Complications in Immunocompromised Individuals
Adults with weakened immune systems, such as cancer patients or organ transplant recipients, may experience prolonged symptoms and complications similar to children.

Clinical Manifestations in Children
Children, particularly those under the age of five, are highly susceptible to hMPV infections. In this age group, the virus can cause a range of symptoms, from mild upper respiratory tract infections to severe lower respiratory illnesses.

Common Symptoms: Fever, runny nose, cough, pharyngitis, otitis, wheezing, and hypoxia are frequently observed.
• Severe Cases: Infants aged 6 to 12 months are at a higher risk of hospitalization due to severe respiratory complications. The virus can lead to bronchiolitis and pneumonia, necessitating medical intervention.
• Neurological Symptoms: In rare instances, seizures have been reported, indicating the virus’s potential to affect the central nervous system.
Clinical Manifestations in Adults
In adults, hMPV generally presents with milder symptoms, but certain populations are at increased risk for severe disease.
• Common Symptoms: Cough, nasal congestion, hoarseness, sore throat, and fever are typical. These   symptoms often resemble those of the common cold.
• High-Risk Groups: Older adults and individuals with underlying health conditions, such as chronic obstructive pulmonary disease (COPD), asthma, or cancer, may experience more severe respiratory illnesses. In these populations, hMPV can exacerbate existing conditions, leading to significant health complications.

Differences in Immune Response
The disparity in hMPV’s impact between children and adults can be attributed to differences in immune system maturity and pre-existing immunity.
• Children: Young children, especially infants, have immature immune systems and lack prior exposure to the virus, making them more susceptible to severe infections.
• Adults: Adults may have partial immunity due to previous exposures, resulting in milder symptoms. However, age-related immune decline and chronic health conditions can increase susceptibility to severe disease in older adults.

Recent Outbreaks and Epidemiological Trends
Recent data indicate a surge in hMPV cases in northern China, with the virus accounting for a significant percentage of respiratory illness tests and hospitalizations. This increase has been particularly notable among children under 14.
The World Health Organization (WHO) has noted that the rise in respiratory infections, including hMPV, aligns with expected seasonal patterns. Enhanced surveillance and improved diagnostic capabilities have contributed to the increased detection of hMPV cases.

Diagnosis and Treatment
Diagnosis
• RT-PCR Tests: To identify hMPV from nasal or throat swabs.
• Chest X-Rays: For severe cases to check for pneumonia.

Diagnostic Challenges
Diagnosing hMPV can be challenging due to its clinical similarity to other respiratory viruses like influenza and RSV. Molecular diagnostic tests, such as polymerase chain reaction (PCR), are essential for accurate identification. However, limited access to these tests, especially in resource-constrained settings, can impede timely diagnosis and treatment.

Treatment
Currently, there is no specific antiviral treatment for hMPV. Supportive care remains the primary strategy:
  For Children:
1. Oxygen therapy for severe respiratory distress.
2. Hydration and fever management.
  For Adults:
1. Symptom relief with over-the-counter medications.
2. Hospitalization for severe cases with breathing difficulties.

Prevention
Preventive measures are similar to those for other respiratory viruses:
• Hand Hygiene: Regular handwashing with soap and water.
• Respiratory Etiquette: Covering the mouth and nose when coughing or sneezing.
• Avoiding Close Contact: Staying away from individuals exhibiting respiratory symptoms.

Research and Vaccine Development
Research into hMPV is ongoing, with efforts to develop vaccines and improve diagnostic methods. The development of vaccines has been challenging due to concerns about vaccine-enhanced disease, a phenomenon observed with similar viruses in the past.

Conclusion
Human Metapneumovirus presents a significant public health challenge, particularly affecting young children and older adults differently. Understanding these differences is crucial for developing targeted interventions and preventive strategies. Ongoing research and heightened awareness are essential to mitigate the impact of hMPV across diverse populations.

References:
1. Human Metapneumovirus: Epidemiology and genotype diversity in children and adult patients with respiratory infection in Córdoba, Argentina – Dec 2020 – https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0244093
2. Human metapneumovirus: An important cause of respiratory disease in children and adults – 2005 – https://pmc.ncbi.nlm.nih.gov/articles/PMC3347970/
3. Emerging lineages A2.2.1 and A2.2.2 of human metapneumovirus (hMPV) in pediatric respiratory infections: Insights from India – Nov 2024 – https://pmc.ncbi.nlm.nih.gov/articles/PMC11665530/
4. Trends of acute respiratory infection, including human metapneumovirus, in the Northern Hemisphere – dec 2024 – https://www.who.int/emergencies/emergency-events/item/2025-DON550
5. The most important virus hardly anybody talks about – may 2024 – https://virologyresearchservices.com/2024/05/31/the-most-important-virus-hardly-anybody-talks-about/
6. Human metapneumovirus – jan 2025 – https://en.wikipedia.org/wiki/Human_metapneumovirus