Lassa fever
Lassa fever clinical and global spread profile: 13 countries, 30 WHO outbreak events since 1997.
Lassa fever · ICD-10 A962 · ICD-11 1D61 · 30 WHO events across 13 countries (1997–2023).
Top affected countries
| Country | Region | Events | % of global |
|---|---|---|---|
| Nigeria | AFR | 8 | 27% |
| United Kingdom of Great Britain and Northern Ireland | EUR | 3 | 10% |
| Germany | EUR | 3 | 10% |
| Togo | AFR | 3 | 10% |
| Liberia | AFR | 2 | 7% |
| Sierra Leone | AFR | 2 | 7% |
| Netherlands | EUR | 2 | 7% |
| Benin | AFR | 2 | 7% |
| Burkina Faso | AFR | 1 | 3% |
| United States of America | AMR | 1 | 3% |
| Guinea | AFR | 1 | 3% |
| Ghana | AFR | 1 | 3% |
| Sweden | EUR | 1 | 3% |
Distribution by WHO region
| Region | Events | Share |
|---|---|---|
| AFR | 20 | 67% |
| EUR | 9 | 30% |
| AMR | 1 | 3% |
Annual outbreak timeline
| Year | Events | Countries |
|---|---|---|
| 2023 | 1 | 1 |
| 2022 | 4 | 4 |
| 2020 | 1 | 1 |
| 2019 | 2 | 2 |
| 2018 | 2 | 2 |
| 2017 | 4 | 4 |
| 2016 | 6 | 6 |
| 2015 | 1 | 1 |
| 2012 | 1 | 1 |
| 2006 | 1 | 1 |
| 2004 | 1 | 1 |
| 2003 | 1 | 1 |
| 2000 | 3 | 3 |
| 1997 | 2 | 2 |
Peak year: 2016 (6 events).
Decade summary
| Decade | Events |
|---|---|
| 1990s | 2 |
| 2000s | 6 |
| 2010s | 16 |
| 2020s | 6 |
WHO case definition
A disease endemic in large parts of sub-Saharan Western Africa caused by infection with Lassa virus. Infection is mild or asymptomatic in most cases, but can cause severe illness or death. After a prodromal period of 7-10 days (sometimes longer), initial symptoms/signs include fever, malaise, headache, sore throat, vomiting, abdominal pain, and diarrhoea. Subsequently, patients develop high fever, extreme lethargy, oedema of head/neck, encephalopathy, pleural effusion, and ascites. Bleeding into the skin, mucosae and underlying tissues occurs in the severest cases. Deafness occurs in many patients, and the disease is often particularly severe in pregnancy. The overall lethality can reach 15% even among hospitalized patients receiving supportive care. Transmission occurs by inhalation, consumption, or direct contact with excretions and bodily fluids from infected rodents. Diagnosis occurs by identification of Lassa virus in blood samples by molecular or serologic methods.
Countries Affected
13
Outbreak Events
30
Year Range
1997–2023
ICD-10 A962
Lassa fever
Visualization
Global Prevalence Snapshot
Based on WHO Disease Outbreak News events (1997–2023).
Risk Level
