CS330933-A April 19, 2022

Death rate 

from Ebola 

Death rate from 

Lassa fever 

70% 1%

What you need to know about

Lassa Fever

Lassa fever is caused by a virus that is found in West Africa. It was first discovered in

1969 in Lassa, Nigeria when two missionary nurses died.

Lassa fever is mainly found in Sierra Leone, Liberia, Guinea, and Nigeria and is spread by rats. Other 

neighboring countries are also at risk because the type of rat that spreads the virus is also found 

throughout the West African region.

100,000

to 300,000

Estimated number of 

Lassa fever cases in 

West Africa each year 5,000

Estimated 

number of 

deaths

Lassa fever is different from Ebola

Lassa fever is different from Ebola, the disease that is responsible for 

the current outbreak in West Africa. Although Lassa fever and Ebola 

can result in similar symptoms, Lassa fever is less likely than Ebola to 

spread from person to person and is far less deadly. The death rate 

from Lassa fever is approximately 1% versus approximately 70% from 

Ebola. While both diseases are viral hemorrhagic fevers, bleeding and 

severe symptoms are not common in cases of Lassa fever.

Lassa fever is spread by a type of rat in West Africa

Lassa fever is caused by infection with the Lassa virus. The virus is spread by a rat that lives in large numbers 

in west, central, and east Africa. They carry the virus in their urine and droppings and live in homes and areas 

where food is stored.

People can get Lassa fever through

Contact with the urine or 

droppings of an infected rat

Catching and preparing

infected rats as food

Inhaling tiny particles in the air 

contaminated with infected rat 

urine or droppings

RARELY, direct contact with a sick person’s 

blood or body fluids, through mucous 

membranes, like eyes, nose, or mouth

People with Lassa fever are not believed to be contagious before they 

have symptoms. Lassa fever is not spread through casual contact (like 

hugging, shaking hands, or sitting near someone).
Number of cases in 

U.S., to date

The risk of getting Lassa fever in the United States is extremely low

There have only been six cases of Lassa fever in the United States and all have been 

associated with travel to countries known to have the virus. The risk of getting 

Lassa fever in the United States from someone who has traveled to West Africa is 

extremely low. People at greatest risk of getting Lassa fever are those who live in or 

visit Sierra Leone, Liberia, Guinea, and Nigeria and have been exposed to rats.

Signs and symptoms of Lassa fever are usually mild

Signs and symptoms

of Lassa fever

typically occur

1 to 3 weeks

after a person

is infected.

 Most people who are infected have mild symptoms and 

so go undiagnosed. Mild symptoms include slight fever, 

feeling tired and weak, and headache.

 In some people, the disease may cause more serious 

symptoms like bleeding; difficulty breathing; vomiting; 

facial swelling; pain in the chest, back, and abdomen;

and shock.

Only an estimated 1% of all Lassa fever cases result in death.

Lassa fever can be treated

If a healthcare worker suspects Lassa fever in a patient, a laboratory test can diagnose the disease. Ribavirin, 

an antiviral drug, has been used to successfully treat patients with Lassa fever. It is most effective when 

given soon after a patient becomes sick. Patients should also receive supportive care, including maintaining 

their hydration, oxygen levels, and blood pressure, and treatment of any other complicating infections.

If you go to West Africa, prevent Lassa fever by 

keeping away from rats.

If you travel to West Africa, the best way to prevent Lassa fever is to

avoid rats.

You can also

 Put food away in rat-proof containers and keep the home clean to 

discourage rat from entering homes.

 Avoid using these rats as a food source.

 Trap rats in and around homes to reduce rat population.

Remember, the risk of getting Lassa fever in the 

United States from someone who traveled to West 

Africa is extremely low. You can’t get Lassa fever 

through casual contact.