🌍 Endemic West Africa

Lassa Fever — Clinical Guide

Complete clinical guide — patients & healthcare workers
Treatment available · Ribavirin IV effective if < 6 days

100–300K
estimated cases/year
15–25%
CFR in hospitalised
Available
treatment available
5
identified strains
⚠️ Public information — Not a medical device. This page is an information tool based on official WHO, CDC, ECDC and national health agency data. It does not replace medical consultation. If in doubt, call 112 / emergency services.
🚨 If fever + return from West Africa (< 21 days)
Call immediately
112
Emergency services — 24/7
  • 1 Stay home — do NOT go to the emergency room without calling first
  • 2 Call 112 and report your return from West Africa
  • 3 Isolate in a separate room, avoid any physical contact
  • 4 Wait for instructions from the emergency operator

🌡️ When should I be concerned?

⚠️ Call 112 if you meet both criteria:
  1. Fever + return from Sierra Leone / Guinea / Liberia / Nigeria / Mali within the last 21 days
  2. + painful sore throat OR sudden hearing loss OR unexplained bleeding
✅ Lassa does NOT spread through:
  • Air or coughing
  • Bottled water or cooked food
  • Contact with an asymptomatic person
  • Insects or mosquitoes

📅 Day-by-day disease progression

Lassa Fever — incubation 6 to 21 days (median: 10 days)

Prodromal phase — gradual onset (not sudden)

  • Gradual fever (not sudden, unlike Ebola)
  • General malaise, fatigue
  • Headaches
  • Chest pain
  • Asymmetric painful sore throat

⚠️ 80% of cases are mild or asymptomatic. Only 20% progress to severe disease.

Systemic phase (20% of severe cases)

  • Vomiting and diarrhoea
  • Facial oedema
  • 🔔 SENSORINEURAL HEARING LOSS — characteristic sign (25–30% of cases)
  • Proteinuria
  • Bleeding in severe forms

⚠️ Hearing loss can be PERMANENT — major neurological sequela. Key distinguishing sign from other haemorrhagic fevers.

After recovery — risks to know

  • Permanent hearing loss in 25% of recovered patients
  • Persistent fatigue for 2–3 months
  • Virus shed in urine up to 3–4 weeks after recovery

Hygiene precautions maintained for several weeks after clinical recovery.

💊 Key difference from Ebola: A TREATMENT EXISTS

✅ Ribavirin IV — Effective treatment available

Unlike Ebola, Lassa fever has a specific treatment.

  • CFR without treatment: 55% in severe forms
  • CFR with Ribavirin IV started within 6 days: < 5%

→ Every hour counts — call emergency services immediately.

❓ Frequently asked questions

Transmission occurs primarily via the rodent Mastomys natalensis (African rat). Food and water contaminated by its urine or faeces are the main source. Human-to-human transmission is possible through direct contact with blood or body fluids of a sick patient, but Lassa does NOT spread by air, unlike influenza.
YES — this is the main difference from Ebola. Ribavirin IV is effective if started within the first 6 days of symptoms. The mortality rate drops from 55% to less than 5% with early treatment. This is why calling emergency services immediately at the first suspicious signs is crucial.
The two most discriminating signs:
  • Sudden hearing loss → suggests Lassa (25–30% of cases)
  • Massive bleeding → suggests Ebola or Marburg
Geographic area is also key: Lassa = West Africa (Sierra Leone, Guinea, Liberia, Nigeria); Ebola = Central Africa (DRC, Uganda).
The risk is exclusively linked to travellers returning from West Africa. There is no endemic circulation in Europe. Imported cases are very rare but occur each year. Healthcare workers who have cared for a case without adequate PPE may be at risk.

📚 Official sources

Last updated: 19 June 2026 · By Dr Clément MÉDEAU, physician (La Rochelle, France)