Human Metapneomovirus - Cards (ver10)

Summary / Overview

Human metapneumovirus (hMPV) is a respiratory RNA virus closely related to RSV
Causes upper and lower respiratory tract infections in all age groups
Clinical presentation overlaps with RSV, influenza, and parainfluenza
No specific antiviral therapy — management is supportive
Severe disease more likely in infants, elderly, and chronic lung disease patients

Etiology

Human metapneumovirus is an enveloped single-stranded negative-sense RNA virus
Transmission occurs via respiratory droplets, direct contact, and contaminated surfaces
Seasonal circulation — peak in late winter and spring
Virus spreads easily in households, daycare centers, hospitals, and elderly care facilities
High-risk groups: infants, elderly, immunocompromised, chronic lung disease
Co-infection with RSV, influenza, or adenovirus may occur

Pathogenesis

Virus enters via respiratory epithelium of nose and nasopharynx
Attachment mediated by viral fusion (F) protein → entry into epithelial cells
Local epithelial injury leads to mucosal edema and increased mucus secretion
Innate immune activation — interferons, cytokines, chemokines released
Inflammatory cell infiltration (neutrophils, lymphocytes, macrophages) in airway mucosa
Spread to lower respiratory tract → bronchiolitis and pneumonitis
Airway obstruction due to edema + mucus plugging → wheeze and hypoxia
Adaptive immune response develops but is incomplete → reinfection possible

Symptoms

Upper respiratory symptoms predominate initially
• Cough
• Rhinorrhea
• Nasal congestion
• Sore throat
• Mild fever
Lower respiratory involvement (especially in children and elderly)
• Wheezing
• Dyspnea
• Persistent cough

Signs

Fever (low–moderate; may be high in severe LRTI)
Erythematous nasal mucosa and pharynx
Wheezing on auscultation (bronchiolar involvement)
Crackles (crepitations) in pneumonia
Chest retractions in infants (intercostal/subcostal)

Clinical Features

Begins as upper respiratory tract infection in most patients
Progression to lower respiratory tract disease common in infants
Bronchiolitis is a frequent presentation in young children
......

Investigations

Nucleic acid amplification test (RT-PCR) from nasopharyngeal swab — diagnostic test of choice
Antigen detection tests available but less sensitive than PCR
Complete blood count — may show mild leukocytosis or normal counts
Inflammatory markers (CRP, ESR) mildly elevated
Arterial blood gas in severe respiratory distress
Chest X-ray — peribronchial thickening, hyperinflation, patchy infiltrates in LRTI
HRCT chest in severe pneumonia — ground-glass opacities, bronchiolitis pattern

Differential Diagnosis

Respiratory Syncytial Virus (RSV) — similar bronchiolitis pattern in infants
Influenza virus — higher fever, prominent myalgia, systemic toxicity
Parainfluenza virus — croup and upper airway involvement
Adenovirus infection — conjunctivitis and pharyngitis common
COVID-19 — pneumonia with systemic inflammatory features
Rhinovirus — milder upper respiratory illness
Acute asthma exacerbation (non-infectious trigger)

Complications

Bronchiolitis with significant airway obstruction
Viral pneumonia progressing to respiratory distress
Acute asthma exacerbation
COPD exacerbation in chronic lung disease patients
Hypoxia requiring oxygen therapy
Secondary bacterial infection (otitis media, sinusitis, pneumonia)

Treatment

Supportive management is the mainstay of treatment (no specific antiviral therapy available)
Maintain hydration — oral fluids preferred; IV fluids if oral intake inadequate
Oxygen therapy for hypoxia — nasal cannula / high-flow nasal oxygen
Mechanical ventilation in severe respiratory failure
Manage bronchiolitis with supportive care (airway clearance, monitoring)
Monitor high-risk groups closely — infants, elderly, cardiac/respiratory disease, immunocompromised
Secondary bacterial infection treated with appropriate antibiotics
Droplet precautions to prevent nosocomial spread

Prevention

No licensed vaccine currently available
Primary prevention depends on respiratory hygiene and infection control
Surface disinfection in homes, schools, and daycare centers
Avoid close contact with symptomatic individuals
Educate parents about early recognition of respiratory distress in children
Outpatient management suitable for mild and stable cases
Encourage adequate hydration and symptom monitoring at home
Use Mask for healthcare workers and caregivers
Hand hygiene before and after patient contact

Serotypes / Subtypes

Two major genetic lineages identified — Type A and Type B
Type A — associated with more severe disease in some outbreaks
Type B — generally milder but clinically similar presentation
Further divided into sublineages
A1, A2 (A2a, A2b)
B1, B2

Pathology

No key-points marked yet. Add lines like *Important point* in this section.

Radiology / Imaging

Chest X-ray may be normal in mild upper respiratory infection
Perihilar infiltrates common in bronchiolitis
Hyperinflation with flattened diaphragms in small airway disease
Patchy bilateral opacities in viral pneumonia
Atelectasis may occur due to mucus plugging
Severe cases show diffuse interstitial infiltrates
CT chest rarely required — used in complicated or ICU cases
CT findings: ground-glass opacities, bronchiolar wall thickening, tree-in-bud pattern

Notes / Teaching points

Innate immune pathway genes likely involved: TLR7, TLR8, RIG-I, MDA5
Interferon signaling defects may predispose to severe viral LRTI
Airway epithelial integrity genes may influence susceptibility (mucociliary clearance)
Children with recurrent viral bronchiolitis may later develop reactive airway disease
Environmental factors: crowding, daycare exposure, pollution, passive smoking

Begins as upper respiratory tract infection in most patients

Progression to lower respiratory tract disease common in infants

Bronchiolitis is a frequent presentation in young children

......

Recurrent wheeze may occur in susceptible children

Asthma exacerbation triggered by viral infection

Community-acquired viral pneumonia in adults and elderly

COPD exacerbation in chronic lung disease patients

Symptoms overlap significantly with RSV and influenza

Seasonal clustering in late winter and spring

Reinfection possible due to incomplete immunity

Severe disease more common in immunocompromised individuals

Hospitalization required in moderate–severe respiratory distress cases

Respiratory Syncytial Virus (RSV) — similar bronchiolitis pattern in infants

Influenza virus — higher fever, prominent myalgia, systemic toxicity

Parainfluenza virus — croup and upper airway involvement

Adenovirus infection — conjunctivitis and pharyngitis common

COVID-19 — pneumonia with systemic inflammatory features

Rhinovirus — milder upper respiratory illness

Human coronavirus (non-COVID strains) — common cold–like illness

Bacterial pneumonia — focal consolidation, high inflammatory markers

Mycoplasma pneumonia — atypical pneumonia in older children/adolescents

Acute asthma exacerbation (non-infectious trigger)

Foreign body aspiration (in acute unilateral wheeze)

Human metapneumovirus is an enveloped single-stranded negative-sense RNA virus

Belongs to family Paramyxoviridae, genus Metapneumovirus

Transmission occurs via respiratory droplets, direct contact, and contaminated surfaces

Primary infection occurs in early childhood; reinfections occur throughout life

Seasonal circulation — peak in late winter and spring

Virus spreads easily in households, daycare centers, hospitals, and elderly care facilities

High-risk groups: infants, elderly, immunocompromised, chronic lung disease

Co-infection with RSV, influenza, or adenovirus may occur

Immunity is incomplete — repeat infections common

Nucleic acid amplification test (RT-PCR) from nasopharyngeal swab — diagnostic test of choice

Multiplex respiratory viral panel detects hMPV along with RSV, influenza, adenovirus

Antigen detection tests available but less sensitive than PCR

Viral culture rarely used in routine clinical practice

Complete blood count — may show mild leukocytosis or normal counts

Inflammatory markers (CRP, ESR) mildly elevated

Pulse oximetry — assesses hypoxia severity

Arterial blood gas in severe respiratory distress

Chest X-ray — peribronchial thickening, hyperinflation, patchy infiltrates in LRTI

HRCT chest in severe pneumonia — ground-glass opacities, bronchiolitis pattern

Human metapneumovirus is a Paramyxovirus related to RSV

Reinfection is common — immunity after infection is incomplete

Disease severity depends more on host immune response than viral load

Infants, elderly, COPD, asthma, and immunocompromised patients are high-risk groups

Bronchiolitis mechanism similar to RSV — small airway inflammation + mucus plugging

Co-infection with RSV or influenza increases severity

Secondary bacterial infection is uncommon but possible in severe cases

Virus spreads via droplets + contaminated surfaces; survives for hours on fomites

Genetic susceptibility suspected in severe/recurrent infections

Innate immune pathway genes likely involved: TLR7, TLR8, RIG-I, MDA5

Interferon signaling defects may predispose to severe viral LRTI

Airway epithelial integrity genes may influence susceptibility (mucociliary clearance)

Children with recurrent viral bronchiolitis may later develop reactive airway disease

Environmental factors: crowding, daycare exposure, pollution, passive smoking

Future research areas:

• host genetics vs viral strain virulence

• epithelial repair mechanisms after viral injury

• microbiome role in viral susceptibility

• immune memory failure in repeated infections

Virus enters via respiratory epithelium of nose and nasopharynx

Attachment mediated by viral fusion (F) protein → entry into epithelial cells

Replication occurs in ciliated respiratory epithelial cells

Local epithelial injury leads to mucosal edema and increased mucus secretion

Innate immune activation — interferons, cytokines, chemokines released

Inflammatory cell infiltration (neutrophils, lymphocytes, macrophages) in airway mucosa

Spread to lower respiratory tract → bronchiolitis and pneumonitis

Airway obstruction due to edema + mucus plugging → wheeze and hypoxia

Adaptive immune response develops but is incomplete → reinfection possible

Severe disease linked to exaggerated inflammatory response in infants and elderly

RT-PCR from nasopharyngeal swab is the most sensitive diagnostic test

Multiplex respiratory viral PCR panels detect hMPV along with RSV, influenza, adenovirus

Viral antigen detection tests available but less sensitive than PCR

Viral culture possible but rarely used clinically (slow, specialized labs)

Serology (IgM/IgG) mainly for epidemiological studies — not routine clinical diagnosis

CBC findings are nonspecific — mild leukocytosis or lymphopenia may occur

Inflammatory markers (CRP, ESR) mildly elevated in moderate–severe infection

ABG analysis required in severe lower respiratory disease to assess hypoxia

Procalcitonin helps differentiate viral vs bacterial co-infection

No licensed vaccine currently available

Primary prevention depends on respiratory hygiene and infection control

Frequent hand washing reduces transmission

Surface disinfection in homes, schools, and daycare centers

Avoid close contact with symptomatic individuals

Educate parents about early recognition of respiratory distress in children

Outpatient management suitable for mild and stable cases

Encourage adequate hydration and symptom monitoring at home

Hospital infection control is essential

Droplet precautions for admitted patients

Use Mask for healthcare workers and caregivers

Hand hygiene before and after patient contact

Isolation or cohorting to prevent spread in wards

Close monitoring of vital signs and respiratory status in hospitalized patients

Early identification of high-risk groups — infants, elderly, chronic lung disease, immunocompromised

Interprofessional care improves outcomes — physician, nurse, pharmacist coordination

Most patients recover fully with supportive care

Human metapneumovirus (hMPV) is a respiratory RNA virus closely related to RSV

Causes upper and lower respiratory tract infections in all age groups

Major cause of bronchiolitis and viral pneumonia in young children

Also significant in elderly and immunocompromised patients

Clinical presentation overlaps with RSV, influenza, and parainfluenza

Seasonal distribution — late winter and spring predominance

Reinfection common due to incomplete immunity

No specific antiviral therapy — management is supportive

Severe disease more likely in infants, elderly, and chronic lung disease patients

References

PDF

https://www.ncbi.nlm.nih.gov/books/NBK560910/

2026-02-23 10:13:00

Upper respiratory symptoms predominate initially

• Cough

• Rhinorrhea

• Nasal congestion

• Sore throat

• Mild fever

Lower respiratory involvement (especially in children and elderly)

• Wheezing

• Dyspnea

• Persistent cough

• Hypoxia

• High fever

Common pediatric presentations

• Bronchiolitis

• Croup-like illness

• Acute asthma exacerbation

• Viral pneumonia

Adult manifestations

• Community-acquired pneumonia

• Acute asthma exacerbation

• COPD exacerbation

Ear involvement

• Acute otitis media (ear pain, abnormal tympanic membrane)

Gastrointestinal symptoms (less common)

• Diarrhea

• Nausea

• Vomiting

Severe disease risk groups

• Infants and young children

• Elderly (>65 years)

• Immunocompromised patients (HIV, cancer, transplant, immunotherapy)

• Chronic lung disease patients

Supportive management is the mainstay of treatment (no specific antiviral therapy available)

Maintain hydration — oral fluids preferred; IV fluids if oral intake inadequate

Oxygen therapy for hypoxia — nasal cannula / high-flow nasal oxygen

Mechanical ventilation in severe respiratory failure

Manage bronchiolitis with supportive care (airway clearance, monitoring)

Treat asthma/COPD exacerbations as per standard protocols

Monitor high-risk groups closely — infants, elderly, cardiac/respiratory disease, immunocompromised

Secondary bacterial infection treated with appropriate antibiotics

Droplet precautions to prevent nosocomial spread

Most infections are self-limited with full recovery

No approved vaccine currently; candidates under research