Lassa fever

Last update: 2025-03-18

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Key facts

Lassa fever is an acute viral haemorrhagic illness caused by the Lassa virus, a member of the arenavirus family of viruses.
Lassa fever is known to be endemic in Benin, Ghana, Guinea, Liberia, Mali, Sierra Leone, Togo and Nigeria, and may exists in other West African countries.
The overall case-fatality rate for Lassa fever is 1%. However, patients who are hospitalized with severe clinical presentation of Lassa fever may have a case-fatality as high as 15%.

Transmission: Animal-borne, direct or indirect contact (reservoir is rats)

Contact with food or household items contaminated with rodent urine or faeces
Contact with the blood, faeces, vomit, spit, sweat, tears, breastmilk or semen from a person sick with Lassa
Contact can be with objects that have been contaminated with the body fluids from a person who is sick with Lassa (for example, bedding, clothes or needles)
Coming into contact with semen (for example, through sex) from someone who has recovered from Lassa (Lassa can be spread through semen for up to three months after recovery)

Most vulnerable to severe consequences

Pregnant women and their unborn babies are at high risk of serious disease and bad outcomes

Most vulnerable to contracting the disease

People living in places where they come into contact with rodents and their urine or faeces, especially in crowded homes with poor sanitation.
Family and relatives of people who are sick (or who have died) from Lassa
Health workers and laboratory personnel who work with people sick with Lassa (especially if the proper precautions are not in place)

General symptoms ( most people infected with Lassa fever show no symptoms )

Fever (sometimes)
Weakness and fatigue (sometimes)
Headache (sometimes)
Sore throat (sometimes)
Muscle pain (sometimes)
Chest pain (sometimes)
Nausea, vomiting (sometimes)
Diarrhoea (sometimes)
Cough (sometimes)
Abdominal pain (sometimes)

Symptoms of severe Lassa

Facial swelling
Bleeding from the mouth, nose, vagina or anus
Seizures
Shaking
Confusion
Unconsciousness
Deafness

What can you do to prevent and control an epidemic?

Reservoir control and prevention

Promote the use of rodent traps inside and outside homes
Promote the use of other rodent control measures such as keeping cats
In some communities, rats are abundant, and it may be difficult to eliminate them from the environment, therefore, in addition to rodent control measures, it is advisable to continue to store foodstuffs in rodent-proof containers, disposing household waste far from the home, and maintain clean households

Monitoring the community and identifying sick people

Identify and immediately isolate sick people

Treatment and management

Immediately refer suspected cases to treatment centres
Support contact tracing and follow-up of contacts
Provide psychosocial support to the sick person, their families and communities
Support safe and dignified funeral and burial practices for Lassa fever

Safe shelters and spaces

Promote secured spaces and prevent rodents from entering houses or accessing stored food and water (including pet or animal food)
Follow recommended environmental hygiene practices
- Dispose of rubbish in rodent-proof containers to minimize possible nesting sites
- Clean and disinfect areas where there is evidence of rodents
- Follow kitchen hygiene practices (for example, clean floors and wash dishes and utensils immediately)

Sanitation and waste management

Encourage disinfection of homes and other spaces with evidence of rodents
Encourage disinfection of homes and other spaces where people have been sick or died from Lassa
Promote disinfection of reusable supplies
Solid waste management
- Encourage the community to clear away rubbish and garbage
- Encourage safe disposal of contaminated waste (by burning or burying)
- Promote proper and safe disposal of dead rodents

Personal protection and hygiene

Promote handwashing in communities and in health centres with soap, chlorine solution or hand sanitizer
Practise and promote social distancing
Promote the use of personal protective equipment (PPE) and disinfectants when cleaning up rodent droppings and nesting materials
Healthcare professionals caring for patients with suspected or confirmed Lassa fever should apply extra personal protection to prevent contact with the patient’s blood and body fluids and contaminated surfaces or materials such as clothing and bedding
Samples taken from humans and animals to investigate Lassa fever should be handled by trained laboratory staff and processed in well-equipped and protected laboratories.

Food hygiene and safety

Discourage rodents as a food source

Social mobilization and behaviour change

Find out the specific advice being given by health and other relevant authorities
- Involve the community in managing rumours and misinformation
- Promote the use of condoms for at least three months after a diagnosis of Lassa
- Promote the safe disposal (burning or burying) of contaminated materials
- Promote safe and dignified burials (discuss with your manager to follow national protocols and guidance)
Model following this advice and inform community members of current health practice advice
Offer support and encouragement to follow the advice
- Try to gain understanding about if and why health practice advice is not being followed
- With the guidance of your supervisor and health authorities, work with communities to overcome barriers to following health advice and recommended practices

Mapping and community assessment

Make a map of the community.
Mark the following information on the map:
- How many people have fallen sick with Lassa? Where?
- How many people have died? Where? When?
- Where are the local health facilities and services? (include traditional healers)
- Where do people obtain their drinking water?
Record the following information on the back of the map:
- When did people start to fall sick with Lassa?
- How many people live in the affected community?
  - How many pregnant women live in the affected areas?
- Are there rats observed in the community households? How common is this?
- How do people in the community store their food?
  - Are rats or other rodents able to eat it or contaminate it?
- How do people in the community dispose of rubbish and solid waste? (put communal rubbish disposal sites on the map)
  - Have the authorities established a reservoir control programme?
  - Do community members have any risky habits or practices when they come into contact with live or dead rodents?
- How do people dispose of dead rodents? (for example, are they buried, thrown in the river, burned?)
- What handwashing facilities are available? (put communal handwashing stations on map)
  - Do they have soap?
- What are the community’s habits, practices and beliefs about caring for sick people? Consider any differences in roles and responsibilities between men and women.
- What are the community’s burial traditions, funeral procedures and practices?
- Do people in the community know about Lassa?
  - Do people know the main signs of Lassa fever?
  - Do they know what to do if someone becomes sick (for example phone number to call, actions to take)?
  - Do people know how to protect themselves from Lassa?
- Is a social mobilization or health promotion programme in place?
- Are people in the community socially distancing? Why? Why not?
- Which sources do people use/trust the most for information?
  - Are there rumours or misinformation about Lassa fever? What are the rumours?
- Are health workers, volunteers or people who have survived Lassa fever stigmatized, left out, threatened or harassed?

Volunteer actions

01. Community-based surveillance 02. Community mapping 03. Communicating with the community 04. Community referral to health facilities 05. Volunteer protection and safety 06. Personal protection equipment (PPE) for highly infectious diseases 09. Preparing oral rehydration solution (ORS) 19. Psychosocial support 20. Isolating sick people 28. Physical distancing 29. Hygiene promotion 31. Good food hygiene 34. Handwashing with soap 35. Handwashing in a highly infectious epidemic 36. Vector and reservoir control 38. Waste disposal and clean-up campaigns 41. Handling and slaughtering animals 42. Promoting safe sex 43. Social mobilization and behaviour change

Other resources

WHO – World Health Organization; Lassa fever; 2017