What symptoms might I have from Lassa fever?

About 80% of people exposed to the Lassa virus do not have any symptoms. If there are symptoms, they often start with fever and generally feeling ill. More symptoms may develop a few days later, such as:

• headache
• sore throat
• muscle pain
• coughing
• reddened eyes
• chest pain
• nausea
• vomiting
• diarrhoea
• stomach pain

Some people also suffer from other symptoms as well, such as:

• mouth ulcers on the inside of the cheek
• throat infection
• swollen lymph nodes: lumps in the throat, armpit or groin
• hearing loss, sometimes in combination with balance problems

Hearing loss caused by Lassa fever is permanent in about 50% of cases.

About 10% of patients with Lassa fever will develop severe symptoms. Examples include facial swelling, fluid in the longs and difficulty breathing. These patients could also suffer from haemorrhaging or organ failure, or could go into shock or fall into a coma. The symptoms can sometimes be so severe that the patient dies as a result. This happens in about 2% of cases.

Who has a higher risk of contracting Lassa fever?

Care workers (such as tropical medicine doctors or nurses) who treat patients that are seriously ill as a result of Lassa fever also have a higher risk of contracting the disease. They are more likely to have contact with the patient’s bodily fluids.

Who is in great danger from Lassa fever?

Lassa fever is very dangerous to newborn babies. The disease is almost always fatal in newborns. Young children also have a high risk of death from the disease. The risks are also higher during pregnancy. Lassa fever can cause a higher risk of mortality or miscarriage.

How does Lassa fever spread?

The Lassa virus is spread by certain types of mice (multimammate mice) that are found in Africa. These mice are not found in the Netherlands. Travellers can be exposed to the virus if they have contact with urine or droppings from these mice.

Human-to-human transmission is also possible. People can only infect others with the Lassa virus if they are ill themselves. People are exposed through contact with bodily fluids. If a person has contact with blood, vomit, stool (poop) or urine from an infected person, they could also contract the virus and become ill. The risk of infecting others is highest if patients are seriously ill and suffer from diarrhoea and haemorrhaging.

The Lassa virus can also be found in the sperm or vaginal discharge of an infected person, and can survive for a long time in those fluids. Even after recovery, it is therefore advisable to continue using a condom during sex for a while longer. 
The time between exposure and illness is between 5 days and 3 weeks.

How can I prevent Lassa fever?

If you are visiting a country where Lassa fever is found, avoid contact with mice and their urine and droppings whenever possible. Store food in well-closed, mice-proof containers and keep your accommodations clean. If you find a dead mouse, dispose of it safely: wear gloves and a face mask that covers the mouth and nose, and use a cleaning agent or disinfectant afterwards. Wash your hands thoroughly when you are done.

These measures are also important when you are doing work that may include contact with mice-contaminated material.

Is there any treatment for Lassa fever?

There is no official treatment for Lassa fever. Patients mainly receive supporting treatment, such as supplementary fluids, blood transfusions and symptom-based treatment.

Antiviral medicines are sometimes used, but experts are not sure whether they actually work well or are safe. That is why patients mainly receive care aimed at supporting their body during their illness.

How common is Lassa fever in the Netherlands?

Lassa fever is very rare in the Netherlands. The disease mainly occurs in parts of West Africa. In the past 40 years, there have been three confirmed cases of Lassa fever in the Netherlands. All three of these people contracted the disease in another country.

What does the Netherlands do to prevent Lassa fever from spreading?

To prevent Lassa fever from spreading in the Netherlands, patients receive care and treatment in isolation. They are admitted to a special isolation ward set up in the hospital, with strict protective measures in place.

The Municipal Public Health Service (GGD) also does source and contact tracing. This means that the GGD checks who the patient has encountered and reaches out to these people. The patient’s contacts need to monitor their own health carefully. If they develop symptoms that could indicate Lassa fever, they will also need to go to an isolation ward to be tested, and receive care and treatment if necessary.