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# Arenaviruses (Lassa and the South American haemorrhagic fevers)

- Virus
- Enveloped
- Contact
- Droplet
- For completeness

Rodent-borne viruses that cause haemorrhagic fevers: Lassa in West Africa and Junín, Machupo, Guanarito and Sabiá in South America.

Updated 2026-11-01

Also called: Lassa fever, Argentine haemorrhagic fever, Bolivian haemorrhagic fever, Venezuelan haemorrhagic fever

## Key points

- Arenaviruses: two-segment ambisense RNA, internal "sandy" ribosomes.
- Reservoir: rodents; Lassa in West African Mastomys.
- Lassa leaves sensorineural deafness in many survivors.
- South America: Junín (Argentina), Machupo (Bolivia), Guanarito (Venezuela), Sabiá (Brazil).

## At a glance

**Shape**
Spherical or pleomorphic, with internal ribosome granules ("sand")

**Genome**
Single-stranded, ambisense RNA, two segments

**Envelope**
Enveloped

**Family**
Arenaviridae (genus Mammarenavirus)

**Size**
About 50 to 300 nm

## Morphology

- Particles containing host ribosomes, which look like grains of sand under the microscope
- Two RNA segments (S and L) with an ambisense strategy
- Also includes lymphocytic choriomeningitis virus of the house mouse

## Transmission

- Contact with or inhalation of rodent urine, droppings or nests; contaminated food
- Rodent bites or scratches
- Lassa and Machupo can spread from person to person through blood and body fluids, mostly in hospitals with poor infection control

**Reservoir:** Rodents, each virus with its own species: Mastomys for Lassa; field mice for Junín, Machupo and Guanarito

### 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

- Infects macrophages and dendritic cells and suppresses the early immune response
- Endothelial damage with capillary leak, bleeding and shock
- Lassa can damage the inner ear: deafness in survivors

## Diseases it causes

- Lassa fever [Viral haemorrhagic fevers (Ebola and others) →](https://durgical.com/en/conditions/viral-haemorrhagic-fevers/)
- South American haemorrhagic fevers (Argentine, Bolivian, Venezuelan, Brazilian) [Viral haemorrhagic fevers (Ebola and others) →](https://durgical.com/en/conditions/viral-haemorrhagic-fevers/)

## Clinical picture

- Incubation of 2 to 21 days with gradual onset of fever, weakness and headache
- In severe cases: bleeding, hypotension, shock, seizures and coma
- Lassa: most infections are mild; deafness in up to a quarter of survivors
- More severe in pregnancy

## Diagnosis

- RT-PCR, antigen or antibody ELISA
- Samples are a high biohazard: maximum-containment laboratories
- Early on it is confused with malaria and other fevers

## Treatment

Intensive supportive care. Ribavirin has been used in Lassa fever, although its benefit is uncertain; convalescent plasma is used in Argentine haemorrhagic fever.

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

- Store food in closed containers and control rodents in the home
- Barrier measures against blood and body fluids in hospital
- Junín virus vaccine in Argentina for people at risk

## Memory aid

"Sand in the granary": arenaviruses carry sand inside and come from the granary mouse; Lassa also takes the hearing.

## Test yourself

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

## What is the reservoir of Lassa virus?

The Mastomys rat (multimammate rat) of West Africa.

## Which sequel is characteristic of Lassa fever in survivors?

Sensorineural deafness, often permanent.

## Which arenavirus causes Venezuelan haemorrhagic fever?

Guanarito virus.

## Which antiviral has been used in Lassa fever?

Ribavirin, although its efficacy is not well established.

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

## Related

- [Hantavirus](https://durgical.com/en/microbiology/hantavirus/)
- [Ebola and Marburg viruses (filoviruses)](https://durgical.com/en/microbiology/ebola-and-marburg-viruses/)
- [Yellow fever virus](https://durgical.com/en/microbiology/yellow-fever-virus/)

## Related conditions

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

## 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: [Lassa fever](https://www.who.int/news-room/fact-sheets/detail/lassa-fever) (WHO, 2024); [About Viral Hemorrhagic Fevers | Viral Hemorrhagic Fevers (VHFs) | CDC](https://www.cdc.gov/viral-hemorrhagic-fevers/about/index.html) (CDC, 2024).

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Representative model, for educational purposes only.

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