Lassa fever

What is lassa fever?

Lassa fever is an acute viral illness caused by the lassa virus, which is known to be endemic in parts of West Africa including Benin, Ghana, Guinea, Liberia, Mali, Nigeria, and Sierra Leone, but likely exists in other West African countries as well.

In endemic countries, lassa fever cases typically peak during the dry season from November to May. About 100,000 to 300,000 cases occur per year in West Africa, with an estimated 5,000 deaths per year.

How is lassa fever transmitted?

Transmission can occur through direct contact with infected rodents or inhalation of aerosols from rodent excretions. Human-to-human transmission can occur through direct exposure to blood or other bodily fluids from an infected person, or through sexual transmission.

Infected individuals become infectious once they begin to develop symptoms.

What are the symptoms of lassa fever? 

Initial symptoms include:

• Gradual onset of fever

• General weakness

• Sore throat

• Headache

• Back/chest/joint pain

• Nausea

• Vomiting

• Diarrhoea

• Cough

Severe features include

• Severe abdominal pain and vomiting

• Conjunctivitis (Pink eye)

• Facial and neck swelling

• Pulmonary fluid build up

• Bleeding

• Shock

• Encephalitis (inflammation of the brain)

• Multi-organ failure

What are the risk factors?

Risk factors include:

• Exposure to rats, rodent droppings, or food contaminated by rodent droppings

• Unprotected exposure to blood and body fluids from infected cases or contaminated environment

How is lassa fever treated?

There are currently no licensed vaccines available for lassa fever.

Treatment for lassa fever involves supportive care, including fluid management and treatment of specific symptoms. While there is currently no antiviral drug approved for lassa fever, ribavirin has been given as treatment for lassa fever. Early use of this antiviral medication is recommended.

How to prevent lassa fever?

Lassa fever prevention primarily focuses on minimising exposure to rodents and their habitats. Travellers are advised to adopt the following measures when travelling to endemic regions (West Africa):

• Store grain and food in rodent-proof containers

• Maintain clean living areas including proper disposal of garbage

• Safe preparation of food (e.g. by thorough cooking)

Please refer to Health Advice for Travellers for the full list of precautions to take when travelling.