[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Other RNA viruses](https://durgical.com/en/microbiology/groups/other-rna-viruses/) › Astrovirus and sapovirus

# Astrovirus and sapovirus

- Virus
- Non-enveloped (naked)

## Contact?

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

- For completeness

Two small viruses that cause watery diarrhoea and vomiting, mainly in young children, care homes and closed settings. Most cases pass within days.

Updated Nov 13, 2026

Also called: human astrovirus, Sapporo virus

## Quick facts

**Type**
Virus · [Other RNA viruses](https://durgical.com/en/microbiology/groups/other-rna-viruses/)

**Gram / shape**
Icosahedral

**Spread**
Faecal-oral · Outbreaks in nurseries

**Causes**
Acute viral gastroenteritis

**Treatment**
No specific antiviral

On this page

- The basics Key points
- At a glance
- Morphology
- Transmission
- Memory aid
- What the colours mean

- Clinical Virulence factors
- Diseases it causes
- Clinical picture
- Diagnosis

- Treatment Treatment
- Prevention

- Study Test yourself

- Connections Connections

## Key points

- Both are naked positive-sense RNA viruses
- Astrovirus: star-shaped on electron microscopy; common in young children
- Sapovirus: a calicivirus like norovirus; outbreaks in care homes
- Watery, non-bloody diarrhoea lasting a few days
- Test for them when norovirus is negative; treat with rehydration

## At a glance

**Shape**
Icosahedral: a five- or six-pointed star on electron microscopy (astrovirus); cup-like surface depressions (sapovirus)

**Genome**
Single-stranded, positive-sense RNA

**Envelope**
Non-enveloped (naked)

**Family**
Astroviridae (astrovirus); Caliciviridae, genus Sapovirus (sapovirus)

**Size**
About 28 to 40 nm

## Morphology

- Naked capsids resist drying and many disinfectants, so they survive on surfaces
- Sapovirus is a calicivirus like norovirus; human sapoviruses fall into genogroups GI, GII, GIV and GV
- Astrovirus has several classic human serotypes and newer types (MLB, VA)

## Transmission

- Faecal-oral: person to person, contaminated food, water or surfaces
- Outbreaks in nurseries, schools, long-term care facilities, cruise ships and hospitals
- Winter peaks in temperate countries
- Contact precautions for diapered or incontinent patients and during outbreaks

**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

- Infect mature enterocytes of the small intestine, blunting villi and causing malabsorption and watery diarrhoea
- Little inflammation: stools are not bloody
- In immunocompromised people astrovirus can cause chronic diarrhoea and, rarely, encephalitis

## Diseases it causes

- Acute viral gastroenteritis in children and older adults [Acute (viral) gastroenteritis →](https://durgical.com/en/conditions/acute-gastroenteritis/)
- Outbreaks in long-term care facilities (sapovirus)
- Rare astrovirus encephalitis in immunocompromised patients [Viral encephalitis (herpes simplex encephalitis) →](https://durgical.com/en/conditions/viral-encephalitis/)

## Clinical picture

- Watery diarrhoea is the main symptom, with vomiting less often than norovirus and low fever
- Illness usually lasts 1 to 4 days; the median for sapovirus is about 2 days
- Dehydration is the main risk in infants and frail older adults

## Diagnosis

- Multiplex gastrointestinal PCR panels on stool detect both viruses
- Worth testing for when an outbreak is norovirus-negative
- Electron microscopy (star-shaped or cup-shaped virions) is historical

## Treatment

No specific antiviral: oral rehydration salts or intravenous fluids according to dehydration; antibiotics have no role.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

- [Oral rehydration salts](https://durgical.com/en/pharmacology/oral-rehydration-salts/)

## Prevention

- Handwashing with soap and water (alcohol gels work less well against naked viruses)
- Cleaning surfaces with suitable disinfectants (for example chlorine-based) during outbreaks
- Exclude sick food handlers and staff until after symptoms end
- No vaccine exists

## Memory aid

"Astro is a star, Sapo is a cup": the shapes under the electron microscope; both mean a few days of watery diarrhoea.

## Test yourself

Think of the answer, then tap the question to see it.

## Which virus looks like a star under the electron microscope?

Astrovirus.

## To which family does sapovirus belong?

Caliciviridae, the same family as norovirus.

## When should astrovirus and sapovirus be sought in an outbreak of gastroenteritis?

When tests for norovirus are negative, especially in closed settings such as care homes.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/microbiology/astrovirus-and-sapovirus/)

## 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.

## Connections

## Related 3

- [Norovirus](https://durgical.com/en/microbiology/norovirus/)
- [Rotavirus](https://durgical.com/en/microbiology/rotavirus/)
- [Adenovirus](https://durgical.com/en/microbiology/adenovirus/)

## Related conditions 2

- [Acute (viral) gastroenteritis](https://durgical.com/en/conditions/acute-gastroenteritis/)
- [Viral encephalitis (herpes simplex encephalitis)](https://durgical.com/en/conditions/viral-encephalitis/)

[← Back to the group: Other RNA viruses](https://durgical.com/en/microbiology/groups/other-rna-viruses/)

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Non-Norovirus Viral Gastroenteritis Outbreaks Reported to the National Outbreak Reporting System, USA, 2009–2018](https://wwwnc.cdc.gov/eid/article/27/2/20-3943_article) (CDC, Emerging Infectious Diseases, 2021); [Sapovirus Outbreaks in Long-Term Care Facilities, Oregon and Minnesota, USA, 2002–2009](https://wwwnc.cdc.gov/eid/article/18/5/11-1843_article) (CDC, Emerging Infectious Diseases, 2012).

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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/astrovirus-and-sapovirus/