Menu

What Is Lassa Fever?

Medically Reviewed by Neha Pathak, MD

Lassa fever is a viral disease that’s spread by rats. It mainly affects people in parts of West Africa, where there are about 300,000 cases of Lassa fever and about 5,000 deaths from it each year.

The disease gets its name from the Nigerian town of Lassa, where it was discovered in 1969 after two missionary nurses died.

Most of the time, the Lassa fever virus causes only mild symptoms like fever and headaches. But some people get more serious symptoms like bleeding and trouble breathing. These can be life-threatening.

How Does Lassa Fever Spread?

A type of rodent called the multimammate rat carries the Lassa fever virus in its pee and poop. There are lots of these rats in West, Central, and East Africa. They tend to live in homes and in other areas where people store food.

People risk catching Lassa fever from infected rats if they:

  • Come into contact with the rats’ pee or droppings
  • Catch and prepare the rodents as food
  • Breathe in tiny airborne particles infected with the rats’ poop

It’s rare, but possible, to get Lassa fever from a person who is sick with it. It can happen if their blood or body fluids get into your system through places like your eyes, nose, or mouth. You can’t catch the disease through casual contact, like by holding hands, hugging, or sitting near them.

Experts don’t think people with the virus are contagious before they have symptoms.

The Lassa fever virus can also spread through contaminated medical equipment, like reused needles.

Who’s at Risk for Lassa Fever?

You’re extremely unlikely to catch this disease in the United States.

As of 2015, the U.S. had only six reported cases of Lassa fever. All were linked to people who’d traveled to counties where the virus is more common. Even so, your chances of getting the disease from someone who’s traveled to the U.S. from West Africa is very low.

Your odds of catching it are highest if you encounter infected rats while visiting or living in one of these African countries:

  • Sierra Leone
  • Liberia
  • Guinea
  • Nigeria

What Are the Symptoms of Lassa Fever?

The symptoms usually show up 1 to 3 weeks after you’re infected. Most people have mild ones like:

  • Slight fever
  • Feeling tired and weak
  • Headache

In about 20% of cases, the disease brings on more serious symptoms, like:

  • Bleeding from places like your gums, eyes, or nose
  • Trouble breathing
  • Throwing up
  • Swelling in your face
  • Pain in your chest, back, and belly
  • Shock

Pregnant women are more likely to have severe cases of Lassa fever. The disease can lead to a miscarriage.

About a third of infected people end up with some deafness as a complication of the illness. This seems to be true whether their disease was mild or serious.

Overall, only about 1% of people who get sick with Lassa fever die. But the death rate for women in the late stages of pregnancy go up to 30%. Death from multi-organ failure can happen within 2 weeks after symptoms start.

How Is Lassa Fever Diagnosed?

Doctors usually spot the disease with a blood test. In the early stage of the illness, a nose or throat swab could also help them make the diagnosis.

What Are the Treatments for Lassa Fever?

Your doctor will probably give you an antiviral drug called ribavirin. It works best when you take it soon after you get sick.

You may get this medicine through an IV of take it as a pill.

If you have a serious case of Lassa fever, you may need hospital care. There, doctors and nurses can:

  • Keep you hydrated
  • Give you extra oxygen
  • Keep your blood pressure in check
  • Treat other health problems you may have

How Can You Help Prevent Lassa Fever?

If you travel to West Africa, the best way to lower your chances of getting the disease is to stay away from rats.

You can take safety measures like these:

  • Store food in rat-proof containers.
  • Keep the place where you’re staying clean, so critters are less tempted to wander in.
  • If you spot rats inside, either stay somewhere else or set up rat traps.
  • Never try to cook or eat rats.

Show Sources

SOURCES:

CDC: “What You Need to Know About Lassa Fever,” “Lassa Fever: Signs and Symptoms,” “Lassa Fever: Diagnosis,” “Lassa Fever: Treatment.”

UpToDate: “Lassa Fever.”

University of California, San Francisco: “ELISA Blood Test.”

Mayo Clinic: “COVID-19 Diagnostic Testing.”

Transactions of the Royal Society of Tropical Diseases and Hygiene: "Lassa fever in pregnancy: a systematic review and meta-analysis."

© 2022 WebMD, LLC. All rights reserved. View privacy policy and trust info