[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [RNA arboviruses](https://durgical.com/en/microbiology/groups/rna-arboviruses/) › Other bunyaviruses

# Other bunyaviruses

- Virus
- Enveloped

## Contact?

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

## Droplet?

Surgical mask within about a metre; single room.

- For completeness

Viruses spread by mosquitoes, sandflies or ticks. They range from childhood encephalitis and summer meningitis to haemorrhagic fevers.

Updated Nov 13, 2026

Also called: La Crosse virus, Toscana virus, sandfly fever viruses, Rift Valley fever virus, Crimean-Congo haemorrhagic fever virus, CCHF

## Quick facts

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

**Gram / shape**
Spherical

**Spread**
La Crosse · Toscana and sandfly fever viruses · CCHF

**Causes**
La Crosse encephalitis · Sandfly fever

**Treatment**
Supportive care for all

On this page

- The basics Key points
- At a glance
- Morphology
- Transmission
- In Colombia
- 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

- Bunyavirales: enveloped, segmented (three-part) negative-sense RNA viruses
- La Crosse: childhood encephalitis in the United States, tree-hole Aedes mosquito
- Toscana: sandfly-borne summer meningitis in the Mediterranean
- Rift Valley fever: livestock and mosquitoes; retinitis and haemorrhagic forms
- CCHF: Hyalomma ticks; nosocomial spread through blood; ribavirin of uncertain benefit

## At a glance

**Shape**
Spherical

**Genome**
Single-stranded, negative-sense (partly ambisense) RNA in three segments (L, M, S)

**Envelope**
Enveloped

**Family**
Order Bunyavirales: Peribunyaviridae (La Crosse), Phenuiviridae (Toscana, sandfly fever, Rift Valley fever), Nairoviridae (CCHF)

**Size**
About 80 to 120 nm

## Morphology

- Envelope with two glycoproteins (Gn and Gc) and three helical nucleocapsids
- The segmented genome allows reassortment between related viruses
- Unlike most family members spread by arthropods, hantaviruses (same order) come from rodents

## Transmission

- La Crosse: Aedes triseriatus (tree-hole mosquito) in the eastern and midwestern United States; chipmunks and squirrels amplify it
- Toscana and sandfly fever viruses: Phlebotomus sandflies around the Mediterranean, April to November
- Rift Valley fever: blood and organs of infected livestock (slaughter, birthing) and Aedes or Culex mosquitoes in Africa and Arabia
- CCHF: Hyalomma tick bites or the blood of infected livestock in Africa, the Balkans, the Middle East and Asia
- CCHF also spreads person to person through blood and body fluids, including in hospitals: contact and droplet precautions

**Reservoir:** Chipmunks and squirrels (La Crosse); Livestock and Aedes eggs (Rift Valley fever); Hyalomma ticks and livestock (CCHF); Sandflies (Toscana)

**Vector:** Aedes triseriatus (La Crosse); Phlebotomus sandflies (Toscana, sandfly fever); Aedes and Culex mosquitoes (Rift Valley fever); Hyalomma ticks (CCHF)

### Isolation precautions

What the care team adds to standard precautions.

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

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

## Virulence factors

- La Crosse and Toscana are neurotropic, causing encephalitis or meningitis
- Rift Valley fever virus targets the liver; a minority develop retinitis, encephalitis or haemorrhagic fever
- CCHF virus damages endothelium and the liver and triggers coagulopathy, with bleeding and multiorgan failure

## Diseases it causes

- La Crosse encephalitis, mostly in children under 16 [Viral encephalitis (herpes simplex encephalitis) →](https://durgical.com/en/conditions/viral-encephalitis/)
- Toscana virus aseptic meningitis in summer [Viral (aseptic) meningitis →](https://durgical.com/en/conditions/viral-meningitis/)
- Crimean-Congo haemorrhagic fever and haemorrhagic Rift Valley fever [Viral haemorrhagic fevers (Ebola and others) →](https://durgical.com/en/conditions/viral-haemorrhagic-fevers/)
- Sandfly fever (a short febrile illness) and Rift Valley fever retinitis

## Clinical picture

- La Crosse: fever, headache and vomiting; a few children develop seizures and encephalitis, with low mortality
- Toscana: fever, headache and stiff neck; among the commonest causes of summer meningitis in southern Europe
- Rift Valley fever: usually a flu-like illness; under 2% develop retinal lesions and under 1% haemorrhagic fever with about 50% fatality
- CCHF: sudden fever, myalgia and photophobia, then petechiae, large bruises and bleeding; about 30% fatality, deaths in the second week

## Diagnosis

- RT-PCR on blood or CSF early in illness; IgM ELISA later
- CCHF and Rift Valley fever samples are a biohazard needing maximum containment
- Thrombocytopenia, leukopenia and raised liver enzymes in CCHF and Rift Valley fever
- Neutralization tests sort out cross-reactions between related viruses

## Treatment

Supportive care for all; there is no approved specific antiviral. Ribavirin has been used off-label for CCHF, but its benefit is uncertain.

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

In Pharmacology:

- [Ribavirin](https://durgical.com/en/pharmacology/ribavirin/)

## Prevention

- Mosquito and sandfly bite avoidance; remove tree-hole and container breeding sites (La Crosse)
- Tick checks, repellents and light-coloured clothing in CCHF areas
- Gloves and protective gear for slaughter, birthing and veterinary work; avoid raw milk
- Barrier nursing and safe injection practices to prevent hospital spread of CCHF
- Rift Valley fever: animal vaccines prevent outbreaks; no licensed human vaccine

## In Colombia

In Colombia these four matter mainly in returning travellers. A related orthobunyavirus, Oropouche virus, does circulate in the Amazon and other regions of the country.

## Memory aid

"Three segments, four vehicles": tree-hole mosquito (La Crosse), sandfly (Toscana), herd and mosquito (Rift Valley), tick (Crimean-Congo).

## Test yourself

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

## Which tick genus transmits Crimean-Congo haemorrhagic fever virus?

Hyalomma ticks.

## Which bunyavirus is a frequent cause of summer aseptic meningitis in southern Europe?

Toscana virus, transmitted by Phlebotomus sandflies.

## What eye complication is typical of Rift Valley fever?

Retinal lesions (retinitis) that can cause permanent vision loss if the macula is involved.

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

## 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 4

- [Oropouche virus](https://durgical.com/en/microbiology/oropouche-virus/)
- [Hantavirus](https://durgical.com/en/microbiology/hantavirus/)
- [Ebola and Marburg viruses (filoviruses)](https://durgical.com/en/microbiology/ebola-and-marburg-viruses/)
- [Arenaviruses (Lassa and the South American haemorrhagic fevers)](https://durgical.com/en/microbiology/arenaviruses/)

## Related conditions 3

- [Viral encephalitis (herpes simplex encephalitis)](https://durgical.com/en/conditions/viral-encephalitis/)
- [Viral (aseptic) meningitis](https://durgical.com/en/conditions/viral-meningitis/)
- [Viral haemorrhagic fevers (Ebola and others)](https://durgical.com/en/conditions/viral-haemorrhagic-fevers/)

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

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

Sources: [Crimean-Congo haemorrhagic fever](https://www.who.int/news-room/fact-sheets/detail/crimean-congo-haemorrhagic-fever) (World Health Organization (WHO), 2022); [Rift Valley fever](https://www.who.int/news-room/fact-sheets/detail/rift-valley-fever) (World Health Organization (WHO), 2023); [About La Crosse Virus](https://www.cdc.gov/la-crosse-encephalitis/about/index.html) (CDC, 2024); [Toscana virus infection](https://www.ecdc.europa.eu/en/toscana-virus-infection) (European Centre for Disease Prevention and Control (ECDC), 2023).

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Representative model, for educational purposes only.

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