Microbiology · Other viruses and prions
Parainfluenza virus !
- Virus
- Enveloped
- Contact
- Exam priority: medium
A common respiratory virus that gives young children croup: barking cough, hoarseness and noisy breathing from an inflamed larynx.
Updated 2026-11-01
Also called: human parainfluenza virus
At a glance
- Shape
- Pleomorphic, helical nucleocapsid
- Genome
- Single-stranded, negative-sense, non-segmented RNA
- Envelope
- Enveloped
- Family
- Paramyxoviridae (types 1 to 4)
- Size
- About 150 to 200 nm
Morphology
- Envelope with the HN (haemagglutinin-neuraminidase) glycoprotein and the F fusion protein
- Helical nucleocapsid
- Types 1 and 2 are linked mainly to croup; type 3 to bronchiolitis and pneumonia in infants
Transmission
- Respiratory droplets from coughs and sneezes
- Direct contact and contaminated surfaces carried to mouth, nose or eyes
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
- HN binds sialic acid on the respiratory epithelium
- The F protein fuses cells and forms syncytia
- Inflammation of the subglottis, the narrowest part of a child's airway, causes the obstruction
Diseases it causes
- Croup (laryngotracheobronchitis) Croup (laryngotracheobronchitis) →
- Bronchiolitis and pneumonia in infants (mainly type 3) Bronchiolitis (RSV) →
Clinical picture
- Children aged 3 months to 5 years after a preceding cold
- Barking cough, hoarseness and inspiratory stridor that worsens at night
- In adults it is usually a mild cold
Diagnosis
- Clinical diagnosis in typical croup
- Neck X-ray: subglottic narrowing, the "pencil point" or "steeple sign"
- Multiplex PCR of nasopharyngeal secretions when it changes management
Treatment
No specific antiviral. Croup is managed with corticosteroids (dexamethasone) and, when moderate or severe, nebulised epinephrine, plus oxygen if needed. Antibiotics do not help.
Drug class only; doses and regimens are set by the clinician from the current guideline.
In Pharmacology:
Prevention
- Handwashing and surface cleaning
- No vaccine
Test yourself
Think of the answer, then tap the question to see it.
Which virus is the commonest cause of croup?
Parainfluenza virus, mainly types 1 and 2.
Which radiological sign is described in croup?
The steeple or pencil-point sign: narrowing of the subglottic trachea on a frontal neck X-ray.
Which medicines are used to manage croup?
Corticosteroids such as dexamethasone and, in moderate or severe cases, nebulised epinephrine.
Which isolation precautions are used for an infant hospitalised with parainfluenza?
Standard and contact precautions.
Related
Related conditions
← Back to the group: Other viruses and prions
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: About Human Parainfluenza Viruses | HPIVs | CDC (CDC, 2024); Croup: MedlinePlus Medical Encyclopedia (MedlinePlus (NLM), 2024).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.