Lassa fever: information sheet for category 1 contacts
Information have been in possible contact with the Lassa virus.
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You have been given this information sheet because you have been in possible contact with with someone infected with Lassa virus, a virus that causes a disease called Lassa fever, or contact with materials contaminated with Lassa virus. As your exposure has been assessed as very low risk, it is very unlikely that you have caught Lassa virus, and you can continue your usual activities. However, as a precaution, if you feel unwell with a fever (temperature of 37.5°C or higher) or other symptoms suggestive of Lassa fever within 21 days of your last exposure to Lassa virus, call NHS 111 and tell them that you have been in possible contact with Lassa virus.
About Lassa fever
Lassa fever is a rare but serious disease caused by Lassa virus. Lassa virus is endemic in parts of West Africa, particularly Guinea, Liberia, Nigeria and Sierra Leone.
How Lassa virus spreads
Lassa virus can spread by:
- direct contact with the organs, blood, secretions, or other bodily fluids of an infected person for example their vomit, faeces, urine, saliva, or semen (including through sexual transmission)
- contact with objects, such as needles or soiled clothing, that have been contaminated with infected bodily fluids
- contact with infected rodents
Lassa virus is not spread through routine, social contact (such as shaking hands or sitting next to someone) with people who do not have symptoms. There is no evidence that Lassa virus can spread through the air.
It can take up to 21 days from when someone is exposed to the virus for symptoms to appear.
Symptoms of Lassa fever
Lassa virus infection causes only mild or no symptoms in approximately 80% of those infected. When symptoms occur, they range from mild fever with sore throat, to chest pain and later bleeding.
The illness begins with:
- fever (temperature above 37.5°C)
- headache
- sore throat
- generalised aches and feeling unwell
This can be accompanied by:
- cough
- nausea
- vomiting
- diarrhoea
- chest and abdominal pain
- sore, swollen or red eyes
Fever can occur constantly or in peaks. Inflammation of the throat and eyes is common. In some cases, the tonsils and throat become inflamed with white patches and small ulcers. Overall, only about 1% of infections result in death.
Preventing and treating Lassa fever
There is currently no licensed vaccine for Lassa virus. To avoid Lassa virus spreading between people, those caring for individuals with possible or suspected Lassa fever should avoid contact with the patient’s bodily fluids and should wear personal protective equipment (PPE).
Treatment for Lassa fever is with supportive care, including balancing fluids and electrolytes, maintaining the patient’s oxygen status and blood pressure, and treating any other infections they may have at the same time. There are antiviral drugs which, if used early on after the start of symptoms may make the illness less serious for anyone infected. They do not prevent the illness altogether.
Your risk of developing Lassa fever
You are not considered to be at risk of having caught Lassa fever. This is because although you have had contact with someone known to have Lassa fever, their bodily fluids, or potentially infectious materials, you have reported that you have not:
- been in close (less than 2 metres) or direct contact with someone known to have Lassa fever without appropriate PPE, while they had symptoms
- been in direct contact with the body fluids (or items contaminated with body fluids, such as bedding) from someone known to have Lassa fever while they had symptoms, without appropriate PPE
- been in direct contact with the body of someone who died who was known to have Lassa fever, without appropriate PPE
Your family and household contacts are not at risk of catching Lassa virus from you. There are no restrictions on your activities, and there are no monitoring or reporting requirements.
What to do if you become ill
It is extremely unlikely that you have caught Lassa virus. However, if you feel unwell with any of the symptoms of Lassa fever as listed above within 21 days of your possible contact with Lassa virus, stay at home. Take your temperature if you have a thermometer available. It is important to take your temperature before you take any medicines such as paracetamol, ibuprofen or aspirin, as these can reduce your temperature.
After taking your temperature, call NHS 111 and tell them that you have had possible contact with Lassa virus. Let them know if your temperature is 37.5°C or higher. They will arrange for you to be assessed by an appropriate clinician.
In an emergency, you should call 999 and tell them about your symptoms and that you have had possible contact with Lassa virus.
Further information
More information about Lassa fever can be found at:
- UK Health Security Agency: Lassa fever: origins, reservoirs, transmission and guidelines
- World Health Organization: Lassa fever