Microbiology · Respiratory RNA viruses
Respiratory syncytial virus !
- Virus
- Enveloped
- Contact
- Exam priority: medium
A virus that causes colds in adults and bronchiolitis in babies. It is the top reason infants are admitted to hospital with a respiratory infection.
Updated 2026-11-01
Also called: RSV
At a glance
- Shape
- Spherical or filamentous
- Genome
- Single-stranded, negative-sense, non-segmented RNA
- Envelope
- Enveloped
- Family
- Pneumoviridae, genus Orthopneumovirus
- Size
- Pleomorphic, about 150 nm or more (up to several hundred nm)
Morphology
- Envelope with glycoprotein G (attachment) and protein F (fusion), which forms syncytia
- No haemagglutinin or neuraminidase
- Two subgroups, A and B
Transmission
- Contact with secretions on hands, toys and surfaces, where it survives for hours
- Respiratory droplets at short range
- Hospital outbreaks on paediatric wards
Reservoir: Humans
Isolation precautions
What the care team adds to standard precautions.
- Contact
- Gown and gloves; dedicated equipment. For C. difficile, soap-and-water hand washing.
Virulence factors
- Protein F fuses bronchiolar epithelial cells into syncytia
- Epithelial necrosis, mucus and oedema block the infant's small bronchioles
- Immunity after infection is incomplete: reinfection occurs throughout life
Diseases it causes
- Bronchiolitis in infants Bronchiolitis (RSV) →
- Pneumonia in infants, older adults and immunocompromised people
Clinical picture
- Runny nose and poor feeding; cough 1 to 3 days later; then wheeze and breathing difficulty
- Under 6 months: apnoea, irritability or lethargy
- Higher risk in preterm infants, congenital heart disease and chronic lung disease
- In older adults: pneumonia and worsening of COPD, asthma or heart failure
Diagnosis
- Clinical diagnosis of bronchiolitis in infants
- RT-PCR or antigen on a nasopharyngeal aspirate or swab when it changes care or for cohorting
- X-ray with hyperinflation and atelectasis, not essential
Treatment
Supportive: oxygen, hydration, nasal suction and ventilation if needed. Bronchodilators and corticosteroids show no routine benefit in bronchiolitis; inhaled ribavirin is kept for exceptional cases in immunocompromised patients.
Drug class only; doses and regimens are set by the clinician from the current guideline.
Prevention
- Monoclonal antibodies against protein F for infants (nirsevimab; palivizumab in high-risk groups)
- Maternal prefusion F protein vaccine during pregnancy
- Vaccine for older adults in some countries
- Hand hygiene and contact precautions in hospital
Test yourself
Think of the answer, then tap the question to see it.
Which RSV protein forms syncytia and is the target of preventive antibodies?
The fusion protein F.
Which precautions are used for an infant admitted with RSV?
Contact precautions (gown and gloves) on top of standard ones.
Which warning sign can be the first feature of RSV in a very young infant?
Apnoea, sometimes before cough or wheeze appear.
Related
Related conditions
← Back to the group: Respiratory RNA viruses
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Clinical Overview of RSV (CDC, 2025); Appendix A: Type and Duration of Precautions Recommended for Selected Infections and Conditions (CDC, 2024).
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Representative model, for educational purposes only.