Lassa Fever
Lassa fever is a viral illness spread mainly by rodents in parts of West Africa, and it can also pass between people in hospitals without proper precautions.
Snapshot: 9/21/2026, 3:30:49 PM · 1 tracked locations · 4,918 active cases (dataset)
At a glance
Quick facts
- How it spreads
- Rodentborne exposure dominates; secondary transmission occurs through bodily fluids in healthcare and household settings without barrier precautions.
- How serious
- About 5.2 of every 100 confirmed cases died
- Where it's active
- Highest current burden: Nigeria (NG).
- Vaccine / treatment
- Rodent control, food storage hygiene, safe burial practices, and rigorous healthcare PPE and triage reduce risk.
Important
Virus Tracker provides aggregated outbreak monitoring for education and situational awareness. It is not medical advice, a diagnostic service, or a substitute for guidance from qualified health professionals or official public health agencies. Always consult licensed clinicians and authoritative sources for personal health decisions.
Overview
Mastomys rodents shed virus in urine and feces; humans become infected through contact with contaminated food or surfaces. Seasonal peaks align with agricultural and dry-season rodent-human interface patterns. Virus Tracker helps visualize regional case pressure alongside broader viral hemorrhagic fever differential diagnoses in surveillance briefings.
Transmission
Rodentborne exposure dominates; secondary transmission occurs through bodily fluids in healthcare and household settings without barrier precautions.
Symptoms & clinical notes
Fever, weakness, headache, sore throat, and in severe cases bleeding, shock, and organ dysfunction. Early supportive care improves outcomes; ribavirin may be used per protocol.
Prevention & control
Rodent control, food storage hygiene, safe burial practices, and rigorous healthcare PPE and triage reduce risk. Community trust accelerates reporting.
Surveillance context
Integrated human and environmental surveillance with rapid diagnostics strengthens containment. Cross-border coordination limits silent spread along trade routes.
Live dataset
Key metrics
Active cases
4.9K
Deaths
1.3K
How fast it's spreading
25.2%
RisingLassa Fever — global infection heat map
Country shading reflects relative active-case intensity from the current Virus Tracker dataset for this pathogen. Hover countries on desktop for counts.
Darker red = more people currently sick.
Live dataset
Trajectory outlook
Projected case trend with a modeled confidence range.
Projected case trajectory for Lassa Fever, with a shaded confidence range, based on the current Virus Tracker dataset.
Illustrative estimateLive dataset
Top regions by active cases
The 1 tracked location with the most active Lassa Fever cases in the current dataset.
Top 1 tracked location for Lassa Fever by active cases, ranked highest to lowest.
Live dataset
Threat intelligence visuals
Threat matrix
How fast vs. how deadly
Each bubble is a threat. Bigger bubbles mean more people are currently sick.
Where this data comes from
11 of 15 sources are reporting normally.
- 11 healthy sourcesHealthy
- 4 sources downDown
- Data reliability
- 42%
- Confidence-adjusted exposure
- 2.1K
Overall threat level
Where it's hitting hardest
- Nigeria4.9K active · score 22.0
Dataset
Top affected regions
| Location | Active | Deaths | Trend |
|---|---|---|---|
| Nigeria (NG) | 4,918 | 1,340 | Stable |
Frequently asked questions
How do people catch Lassa fever?
Mostly by eating food or touching surfaces contaminated with urine or droppings from infected Mastomys rats. It can also spread between people through contact with infected blood or body fluids.
Is there a vaccine or treatment?
No approved vaccine exists yet. The antiviral drug ribavirin may help if given early, alongside supportive medical care.
How dangerous is Lassa fever?
Most infections are mild or without symptoms, but a minority of cases become severe and can be fatal, particularly late in pregnancy.
Is this page medical advice?
Virus Tracker provides aggregated outbreak monitoring for education and situational awareness. It is not medical advice, a diagnostic service, or a substitute for guidance from qualified health professionals or official public health agencies. Always consult licensed clinicians and authoritative sources for personal health decisions.
What does "outbreak activity" mean on Virus Tracker?
Outbreak activity reflects active-case burden relative to recoveries in our models. It helps compare stressed outbreak zones within the dataset—it is not a clinical score.
How often is this wiki updated?
Figures refresh on the site’s ingestion and revalidation schedule (typically about every 30 minutes in production). Timestamps on the dashboard snapshot indicate the last build of the underlying dataset.
Why might the heat map not match official government totals?
We merge multiple open sources and fallbacks; reporting lag, testing policy, and geographic coverage differ by country. Use national health ministries for authoritative case definitions.
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