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Lassa Fever Fact Sheet

Reviewed August 2017

What is Lassa fever?

Lassa fever is caused by a virus that normally occurs in West Africa (including Guinea, Liberia, Sierra Leone, etc.). There has only been one reported case of Lassa fever in Canada, in 1989. Lassa fever has never been reported in Toronto. Approximately 80% of people infected with the virus experience only mild symptoms or have no symptoms at all. The remaining 20% can have more severe illness and some individuals may die from their infection.

How do people get Lassa fever?

Lassa fever can spread from person-to-person through any bodily fluid, including blood and saliva, once a person becomes symptomatic. The virus cannot be spread through casual contact (including skin-to-skin contact) without exchange of bodily fluids.

What are the symptoms of Lassa fever?

Many different symptoms are associated with Lassa fever, making the diagnosis difficult. Signs and symptoms usually begin one to three weeks after infection with the virus, and include: fever (38oC (101oF), chest pain, sore throat, back pain, cough, stomach pain, vomiting, diarrhea, swollen and red eyes (conjunctivitis), facial swelling, kidney problems (protein in the urine) and bleeding from the mouth and gastrointestinal tract. Neurological effects include hearing loss, tremors, and swelling/infection of the brain (encephalitis).

How serious is Lassa fever? What are the complications?

Lassa fever can be very serious and have severe complications. About 1% of people who become infected with the Lassa fever virus will die. This increases to approximately one in five patients hospitalized with the illness. Pregnant women, particularly those in their third trimester, are at increased risk of death. Miscarriage is common in pregnant women who become infected with Lassa fever.

Hearing loss is the most common complication of Lassa fever. Some degree of deafness, in many cases permanent, occurs in up to one-third of cases. It does not appear that the severity of illness increases the risk of complications; deafness may develop in mild as well as in severe cases.

How is Lassa fever treated?

Ribavirin, an antiviral drug, has been used successfully in individuals with Lassa fever. It has been shown to be most effective when given early in the course of the illness. Patients should also receive supportive care in a hospital as needed.

How can Lassa fever be prevented?

Ill individuals should be kept in isolation in hospital and precautions instituted until they are well. As few staff as possible should attend to patients with Lassa fever, and these staff should wear protective clothing including masks, gloves, gowns, and goggles.

Is there any preventive treatment if I am in contact with a person with Lassa fever?

Yes. Ribavirin, a medication that prevents the development of symptoms of Lassa fever, can be given to people who have been exposed to the illness through close contact with the mucous membranes of an infected person, such as through kissing or sexual intercourse, or through a needle stick or other penetrating injury involving contact with the infected person's secretions, excretions, blood, tissues, or other bodily fluids.

How should the environment around a person with Lassa fever be cleaned and disinfected?

Thorough cleaning and disinfecting the physical environment (room, bed, washroom) of a person confirmed to have Lassa fever is recommended. After cleaning all surfaces, the area should be disinfected with a solution of water and sodium hypochlorite (5% household bleach). To obtain the required concentration, mix 5 ml bleach with 2½ litres water OR 1 tsp bleach with 10 cups water. Leave the disinfectant in place on the surface for at least 10 minute before rinsing. Other products that may be used for low-level disinfecting include quaternary ammonium based products, phenolic chlorine- based products and iodophor formulations.

Lassa fever is reportable in Ontario. If you suspect you have Lassa fever please call Toronto Public Health at 416 338-7600.

Adapted from the CDC - Special Pathogens Branch Lassa Fever Fact Sheet December 2004


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