Lassa Fever

Lassa fever is a type of viral hemorrhagic illness you can get from humans or rats infected with Lassa virus. It’s common in West Africa. Most people get mild symptoms, like fever and headache. But about 1 in 5 people has serious illness. Pregnant people are at especially high risk for serious complications and miscarriage.


What is Lassa fever?

Lassa fever is an illness you get from a virus that’s common in countries of West Africa. Lassa is a type of viral hemorrhagic fever (VHF) , a group of viruses that can cause uncontrolled bleeding. Most people who have Lassa fever have mild symptoms like fever, headaches and fatigue. But about 20% of people who get it are seriously ill. Pregnant people are at especially high risk for miscarriage and other serious complications.

Lassa fever spreads through the poop and pee of infected rats. You can also get it from contact with the body fluids of someone who’s infected.

How common is Lassa fever?

Approximately 100,000 to 300,000 people get Lassa fever in countries of West Africa every year. There haven’t been reports of anyone getting infected in the U.S. or other areas of the world.


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Symptoms and Causes

What are the symptoms of Lassa fever?

About 80% of people with Lassa fever have mild symptoms, including:

  • Fever.
  • Tiredness (fatigue).
  • Cough.
  • Sore throat.
  • Headache.

Another 20% have severe symptoms, including:

What causes Lassa fever?

Lassa virus (LASV) causes Lassa fever. It’s carried by Mastomys (or “multimammate”) rats, which live in countries in West Africa. Lassa virus can damage your blood vessels and lower your blood’s ability to clot, causing uncontrolled bleeding.

How do you get Lassa fever?

You get Lassa fever from contact with infected rat poop (feces) or pee (urine), which can contaminate food or surfaces. You can also get it from contact with body fluids of people infected with LASV. This includes sexual contact or exposure to their poop, pee or blood. Once a person or animal is infected with LASV, it can stay in their pee for a long time.

If there aren’t good sanitation procedures in place, or if personal protective equipment (PPE) isn’t used (or isn’t available), Lassa fever can also spread in healthcare facilities.

What are the risk factors for Lassa fever?

You’re at risk for Lassa fever if you live in or travel to areas in West Africa where it’s common. This includes:

  • Nigeria.
  • Benin.
  • Guinea.
  • Liberia.
  • Mali.
  • Sierra Leone.

Pregnant people are at an especially high risk for complications and death.


What are the complications of Lassa fever?

Even in mild cases, about 1 in 3 people with Lassa fever has partial or complete hearing loss. This may be temporary or permanent.

People with severe Lassa fever can have life-threatening complications. They include:

Diagnosis and Tests

How is Lassa fever diagnosed?

A provider diagnoses Lassa fever by testing samples of your body fluids for signs of the virus. To get samples and perform tests, they might do:

Lassa fever can look like other illnesses — including malaria, dengue and Ebola — so it can be difficult to diagnose. Tell your provider if you’ve traveled to areas where Lassa fever is common or if you could’ve been exposed to the virus.


Management and Treatment

What is the treatment for Lassa fever?

Healthcare providers often treat Lassa fever with the antiviral medication ribavirin. Your provider may also give you other treatments depending on your condition, including:

Lassa virus and pregnancy

Pregnant people need special attention. Most of the time, the fetus can’t survive a Lassa fever infection. Your provider will monitor you for any signs of miscarriage. They’ll need to remove any fetal tissue as soon as possible if a miscarriage happens. This increases the chances that your condition will improve.

Depending on how far along the pregnancy is, your health and the fetus’s health, providers may recommend delivering early. This can improve the chances of survival for both of you.


Can Lassa fever be prevented?

You can reduce your risk of Lassa fever by keeping your living space free of rodents and protecting yourself when you’re around someone who’s infected. Things you can do to reduce your risk include:

  • Avoid contact with rodents, especially in areas where Lassa fever is common. Keep living spaces clean and sanitary, with food in closed containers to discourage attracting rats and other pests.
  • Wear protective coverings when caring for someone who has or might have Lassa fever. This includes a mask, gloves, gowns, non-fogging goggles and boots. Ask a healthcare provider (or your employer if you work in healthcare) what precautions you need to take.
  • If you’re infected with Lassa virus, you should isolate away from others to prevent spreading it.

Outlook / Prognosis

What can I expect if I have Lassa fever?

Healthcare providers and others caring for you will need to take special precautions if you have Lassa fever. This includes wearing protective gear and clothing (like masks, gloves, goggles and aprons) and isolating you from other people.

If you’re pregnant, you need to be treated with antiviral medications right away. Healthcare providers will monitor you very closely. Talk to your provider about what you can expect and what the best treatment options are for your health and the health of your pregnancy.

How long will it take to feel better?

Most cases of Lassa fever are mild. It might take a week or longer to feel better. About half of people with hearing loss regain hearing within a few weeks.

When can I return to work/school?

Even if you have mild symptoms, you shouldn’t be around people while you’re still contagious. Ask a healthcare provider when it’s safe to be around others again.

What is the survival rate of Lassa fever?

Since most people have mild cases of Lassa fever, the survival rate is good. The mortality (death) rate of Lassa fever depends on how severely ill you are and other factors:

  • The mortality rate for all cases (mild and severe) is 1% (1 out of 10 people who have Lassa fever will die from it).
  • For people who need to be hospitalized, the mortality rate is around 15%. During outbreaks, this can be much higher.
  • For pregnant people, the mortality rate is about 33% (or 1 in 3 people).

Living With

When should I see my healthcare provider?

Talk to a healthcare provider right away if you live in or have traveled to countries in West Africa and have symptoms of Lassa fever. If you’re pregnant or think you could be pregnant, a healthcare provider needs to treat and monitor you carefully.

When should I go to the ER?

Go to the nearest emergency room right away — and let them know you might have Lassa fever — if you have severe symptoms, including:

  • Chest, neck or stomach pain.
  • Difficulty breathing.
  • Severe vomiting or diarrhea.
  • Seizures.
  • Confusion.

What questions should I ask my doctor?

It might be helpful to ask a healthcare provider:

  • How do I prevent spreading the virus?
  • What are my treatment options?
  • How do I take care of myself?
  • How long will it take to feel better?
  • What new or worsening symptoms should I look out for?

A note from Cleveland Clinic

You can get Lassa fever if you live in or travel to West African countries. Most cases are mild, but it can cause severe complications, especially in pregnant people. Taking precautions to avoid areas with rats and wearing PPE when caring for someone with Lassa can help reduce your risk. If you’re traveling to a country where Lassa fever is common, it might be helpful to talk to a healthcare provider or public health official about any concerns you have before you travel.

Medically Reviewed

Last reviewed by a Cleveland Clinic medical professional on 06/20/2023.

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