Lassa fever: information sheet for category 4 contacts
Advice for people who have come into contact with Lassa virus.
Get this information as a PDF
You have been given this information sheet because you have had contact with someone infected with Lassa virus, or material contaminated with Lassa virus. Lassa virus causes a disease called Lassa fever. You should follow the advice in this information sheet and check yourself for symptoms for 21 days after your last contact with Lassa virus. If you develop symptoms of Lassa fever within 21 days of your last exposure to Lassa virus, you should stay at home and call your designated contact immediately.
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 takes 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 reported that one or more of the following happened:
- you had direct contact with someone who had Lassa fever without appropriate PPE, or there was a breach in your PPE. This includes exposure to their body fluids, such as blood, vomit, faeces or saliva, or kissing and/or sexual contact
- your skin or mucous membranes were exposed to an environment potentially contaminated with the blood or body fluids of someone who had Lassa fever, including on clothing or bedding, without wearing appropriate PPE
- you had unprotected sexual contact with someone who previously had Lassa fever within 3 months of their illness
- you handled clinical or laboratory specimens from someone who had Lassa fever without adequate protection, for example without appropriate PPE or laboratory practices
We would like to monitor you for a period of 21 days from when you were last exposed to Lassa virus. This will mean that we can act quickly in case you do develop symptoms, reducing the risks to you and to others close to you.
What you need to do
Your family and household contacts are not at risk of catching Lassa virus from you if you do not have any symptoms.
You should take the following actions for the 21 days from when you were last exposed to Lassa virus:
- record your temperature and monitor yourself for other symptoms suggestive of Lassa fever twice per day at the same times each day
- report these temperatures to your designated contact by 12 noon each day. They will want to know whether your temperature is below, equal to, or above 37.5°C, and will arrange further evaluation as necessary. They will explain the local arrangements for accessing healthcare
- if you become ill with any of the symptoms listed above in between reporting to your designated contact, you should phone your designated contact immediately. See below for further information on what you should do if you become ill
- if you are a healthcare worker, you should not have any contact with patients for 21 days after your last exposure. You may need to speak to your line manager about options for redeployment to non-patient facing roles during this period. UKHSA will contact your occupational health department before you can return to a patient facing role
- it is important to avoid close contact with children aged under 18 (where possible; see information below), pregnant women, or those who have a weakened immune system for 21 days after your last exposure. You should avoid close contact with these people both within your household and others outside of your household. If your work involves direct contact with children, pregnant women, or individuals who have a weakened immune system, speak to your line manager about options for re-deployment to other roles
- if you have direct contact with other people as part of your work, speak to your manager about possible options to reduce the amount of contact you have with other people for 21 days from when you were last exposed to Lassa virus, for example remote working
In addition, for the 21 days from when you were last exposed to Lassa virus:
- avoid situations where it would be impossible for you to self-isolate if you became ill (such as crowded public places)
- do not share towels, bed linen, toothbrushes or razors
- avoid sexual contact with other people
- you should postpone any non-essential medical or dental treatment, including vaccination. If you need essential medical or dental treatment, inform your healthcare provider about your exposure to Lassa virus
If you do not have any symptoms during the 21 days from when you were last exposed to Lassa virus, you may undertake the following travel:
- any length of trip by private car within the UK
- local travel on local commuter/public transport, principally for work. However, you should avoid having to travel by public transport if possible, and keep any trips you make as short as possible
- you should not travel internationally, or via air within the UK
If there are children in the household
If you have a child or children in your household, or a child in your household is a close contact of someone with Lassa fever, you should take precautions to minimise direct contact with them as far as you can, while ensuring that you are meeting their care and wellbeing needs. For example, if feasible, another member of the household could take the lead in caring for them during the 21-day period. Children who are contacts should always be given the care and contact they need to ensure their wellbeing.
If you have a holiday planned
If you have a holiday planned within the 21 days since you were last exposed to Lassa virus, you should not travel abroad.
Use of medicines such as aspirin, paracetamol or ibuprofen
Certain medicines, such as paracetamol, ibuprofen and aspirin, can reduce your body temperature during a fever (antipyretic) for up to 8 hours. Thermometer measurements may therefore show a lower temperature than would be expected for up to 8 hours after taking an antipyretic.
You must call your designated contact for further advice if you need to take an antipyretic medicine.
Please take your temperature before you take paracetamol, ibuprofen or aspirin, and if your temperature is 37.5°C or higher, you must call your contact immediately.
A temperature of 37.5°C or higher is always significant, whether you are taking one of these medicines or not, and must be reported urgently.
What to do if you become ill
If you are feeling unwell or develop any of the symptoms of Lassa fever (including a temperature of 37.5°C or higher) in the 21 days from when you were last exposed to Lassa virus, please stay at home. Take your temperature if you have not done this already. Phone your designated contact immediately, who will arrange for you to be assessed by an appropriate clinician. If there is any delay in making contact, phone 111 reporting your recent contact with someone with Lassa fever. In an emergency, you should call 999 and tell them about your symptoms and your recent 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