Merck Manual

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Lassa Fever and South American Hemorrhagic Fevers


Thomas M. Yuill

, PhD, University of Wisconsin-Madison

Reviewed/Revised Aug 2021 | Modified Sep 2022
  • 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 has occurred in Nigeria, Liberia, Guinea, Togo, Benin, Ghana, and Sierra Leone. The South American arenavirus hemorrhagic fevers occur in Bolivia, Argentina, Venezuela, and Brazil.

Caused by arenaviruses Arenaviruses Arbovirus, arenavirus, and filovirus are viruses that are spread from animals to people and, with some viruses, from people to people. The animal involved depends on the type of virus. Many... read more , 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 of Lassa fever and South American arenavirus hemorrhagic fevers 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. Obvious 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 up 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 of Lassa fever or a South American hemorrhagic fever 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. Health care workers are at significant risk of becoming infected when treating hospitalized Lassa fever patients and should wear personal protective equipment. 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 Argentine hemorrhagic fever, a South American hemorrhagic fever caused by the Junin virus.


  • Supportive care, including fluids

  • Ribavirin

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

Drugs Mentioned In This Article

Generic Name Select Brand Names
Copegus, Moderiba, Rebetol, RibaPak, Ribasphere, Ribasphere RibaPak, RibaTab, Virazole
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