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Lassa Fever and South American Hemorrhagic Fevers

By Craig R. Pringle, BSc, PhD, Professor Emeritus, School of Life Sciences, University of Warwick

Lassa fever and South American hemorrhagic fevers are viral infections that cause bleeding (hemorrhage) and organ malfunction. They often result in death.

  • These infections spread from rodents to people, usually when people eat contaminated food.

  • Symptoms may include fever, muscle aches, headache, nausea, vomiting, cough, and sore throat, as well as bleeding from the mouth, nose, or internal organs.

  • To confirm the diagnosis, doctors do blood and urine tests.

  • Treatment includes giving fluids and other treatments to maintain body functions.

Lassa fever and South American hemorrhagic fever are hemorrhagic fevers (see Hemorrhagic Fevers Overview), characterized by bleeding.

Lassa fever has occurred in Nigeria, Liberia, Guinea, and Sierra Leone. The South American fevers occur in Bolivia, Argentina, Venezuela, and Brazil.

Caused by arenaviruses, these infections spread from rodents or their urine or droppings to people, usually when contaminated food is eaten. They can spread from person to person through contact with body fluids (such as saliva, urine, feces, or blood).


Symptoms usually start about 5 to 16 days after people are exposed to the virus. These infections cause fever, a general feeling of illness (malaise), weakness, diffuse body aches, diarrhea, and vomiting. Over the next 4 to 5 days, chest pain, a sore throat, cough, and vomiting may develop. About 80% of cases of Lassa fever are mild and are often not diagnosed. But symptoms are severe in about 20% of people.

If severe Lassa fever may cause the face and neck to swell. About 20% of people with Lassa fever lose their hearing. Loss may be permanent.

Bleeding from the mouth, nose, stomach, and intestinal tract is common in South American hemorrhagic fevers. Overt bleeding is less common in Lassa fever. But bleeding sometimes occurs from puncture wounds, the gums, or the nose and under the skin (seen as small purplish spots). When death occurs, it usually results from shock caused by widespread leakage of fluid from blood vessels.

Recovery or death usually occurs 7 to 31 days after symptoms begin. Lassa fever, if severe, causes death in 16 to 45% of people. In women who are pregnant or have just had a baby, the death rate is higher (up to 92%).


  • Blood tests

These infections are suspected when people who may have been exposed to the virus have characteristic symptoms. The diagnosis is confirmed by blood tests to identify the virus or antibodies to the virus.

Strict isolation is required to prevent spread to health care workers and family members. During an outbreak, quarantining people with symptoms of infection (fever and hemorrhage) has been an effective way to control outbreaks of these infections. Precautions are taken to prevent spread through the air.

No vaccine is available for Lassa fever. An experimental vaccine is effective against some South American hemorrhagic fevers.


  • Supportive care, including fluids

  • Ribavirin

Treatment is supportive care, which includes giving fluids and electrolytes if needed.

The antiviral drug ribavirin does not cure the infection but reduces the risk of death in people with Lassa fever. It may also be beneficial in South American hemorrhagic fevers.