[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Other viruses and prions](https://durgical.com/en/microbiology/groups/other-viruses-and-prions/) › Parainfluenza virus

[Microbiology](https://durgical.com/en/microbiology/) · [Other viruses and prions](https://durgical.com/en/microbiology/groups/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

## Key points

- Croup = barking cough + stridor + hoarseness; commonest cause: parainfluenza.
- X-ray: steeple sign (subglottic narrowing).
- Croup treatment: corticosteroid, and nebulised epinephrine if there is stridor at rest.
- Paramyxovirus with HN and F; no vaccine.

## 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) →](https://durgical.com/en/conditions/croup/)
- Bronchiolitis and pneumonia in infants (mainly type 3) [Bronchiolitis (RSV) →](https://durgical.com/en/conditions/bronchiolitis/)

## 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:

- [Dexamethasone](https://durgical.com/en/pharmacology/dexamethasone/)

## Prevention

- Handwashing and surface cleaning
- No vaccine

## Memory aid

"Para-croup": parainfluenza makes the child bark like a seal, and the X-ray shows a church steeple in the trachea.

## 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.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/microbiology/parainfluenza-virus/)

## Related

- [Respiratory syncytial virus](https://durgical.com/en/microbiology/respiratory-syncytial-virus/)
- [Human metapneumovirus](https://durgical.com/en/microbiology/human-metapneumovirus/)
- [Influenza virus](https://durgical.com/en/microbiology/influenza-virus/)
- [Measles virus](https://durgical.com/en/microbiology/measles-virus/)

## Related conditions

- [Croup (laryngotracheobronchitis)](https://durgical.com/en/conditions/croup/)
- [Bronchiolitis (RSV)](https://durgical.com/en/conditions/bronchiolitis/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

**Contact**
Gown and gloves; dedicated equipment. For C. difficile, soap-and-water hand washing.

**Droplet**
Surgical mask within about a metre; single room.

**Airborne**
N95 respirator and a negative-pressure room.

[← Back to the group: Other viruses and prions](https://durgical.com/en/microbiology/groups/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](https://www.cdc.gov/parainfluenza/about/index.html) (CDC, 2024); [Croup: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000959.htm) (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.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/parainfluenza-virus/