A hemorrhagic fever that kills approximately one in four hospitalized patients is surging in Nigeria in 2026, and American travelers who have recently returned from West Africa may be carrying it without knowing it. As of the end of March 2026, the Nigeria Centre for Disease Control and Prevention (NCDC) confirmed 663 Lassa fever cases and 167 deaths across 22 states and 93 local government areas — with a case fatality rate of 25.2 percent, a sharply elevated figure compared to 18.5 percent during the same period in 2025 and significantly higher than Nigeria's typical baseline.
The outbreak has infected 39 healthcare workers, including physicians, with reported deaths among clinical staff — a signal that infection prevention and control (IPC) measures in healthcare settings are being overwhelmed or inconsistently applied. Eighty-five percent of confirmed cases are concentrated in five states: Bauchi, Ondo, Taraba, Benue, and Edo, but the geographic spread — 22 states — confirms the outbreak has moved well beyond Nigeria's traditional Lassa-endemic core.
The National Emerging Special Pathogens Training and Education Center (NETEC) issued an explicit warning in April 2026 directed at U.S. healthcare facilities: "With increasing international travel, including major global events like the upcoming World Cup, there is a greater likelihood of travelers arriving from endemic regions. While imported cases may be rare, the potential for isolated cases in the U.S. increases with global movement." Recent cases in travelers from the U.S. and South Africa, documented in a Lancet study on underdiagnosis published March 2026, underscore that the disease is not contained within Nigeria's borders.
What Lassa Fever Is and Why It Is So Dangerous
Lassa fever is an acute viral hemorrhagic illness caused by the Lassa virus (LASV), an arenavirus that is endemic in West Africa — particularly Nigeria, Sierra Leone, Liberia, and Guinea — where the Mastomys (multimammate) rat is the primary animal reservoir. Humans are infected primarily through contact with rat urine or feces contaminating food, water, or household surfaces, or through inhalation of dust contaminated with infected rat excretions. Person-to-person transmission can occur through direct contact with blood or bodily fluids of infected individuals — the primary reason healthcare workers face elevated risk.
Approximately 80 percent of Lassa virus infections are mild or asymptomatic. The other 20 percent cause serious illness — fever, severe headache, sore throat, chest pain, nausea, vomiting, diarrhea, cough, abdominal pain, and in severe cases, bleeding from the gums, eyes, nose, or other sites, swelling of the face, fluid in the lungs, and multi-organ failure. The overall case fatality rate among all infected individuals is approximately 1 percent — but among hospitalized patients with symptomatic severe disease, that figure climbs to 15 to 25 percent, consistent with the 25.2 percent rate Nigeria is reporting in 2026.
One particularly devastating complication affects survivors: hearing loss occurs in approximately 25 to 30 percent of patients who recover from Lassa fever, and this loss may be permanent. It represents the disease's highest-burden long-term complication, affecting hundreds of people in endemic communities each year.
Why U.S. Healthcare Providers Must Stay Vigilant
The key message from NETEC for U.S. clinicians is diagnostic awareness. Lassa fever presents in early stages with a non-specific febrile illness that resembles malaria, typhoid, influenza, or other common infections. In a patient who has recently traveled to West Africa — particularly to Nigeria, Sierra Leone, Guinea, or Liberia — and who presents with fever, sore throat, retrosternal chest pain, facial edema, or hemorrhagic manifestations that do not respond to antimalarial treatment, Lassa fever should be on the differential.
There is one FDA-approved treatment: ribavirin, an antiviral medication that significantly improves outcomes when administered early in the course of illness. Its effectiveness is highly time-dependent, making early diagnosis and prompt treatment the most critical factors in reducing mortality.
Any clinician who suspects Lassa fever in a returning traveler should immediately contact their state or local health department and the CDC Emergency Operations Center at (770) 488-7100, isolate the patient with strict infection control precautions, and test only through specialized laboratories designated for viral hemorrhagic fever diagnosis.
Frequently Asked Questions
Q: How deadly is Lassa fever?
A: Among all infected individuals, approximately 1% die. Among hospitalized patients with symptomatic severe disease, the fatality rate is 15–25%. Nigeria's 2026 outbreak has a reported case fatality rate of 25.2%.
Q: How is Lassa fever transmitted?
A: Primarily through contact with food, water, or household surfaces contaminated with urine or feces from infected Mastomys rats. Person-to-person transmission can occur through direct contact with blood or bodily fluids of symptomatic patients.
Q: Is Lassa fever circulating outside of Nigeria?
A: Lassa fever is endemic in Nigeria, Sierra Leone, Liberia, and Guinea. Imported cases have been documented in travelers from the U.S. and South Africa. Cases have been reported in Europe. Imported cases to the U.S. are rare but documented.
Q: Is there treatment for Lassa fever?
A: Yes. Ribavirin is an FDA-approved antiviral treatment that significantly improves outcomes when administered early. Early diagnosis and prompt treatment are critical.
Q: What should travelers who visited West Africa recently do if they feel ill?
A: Seek immediate medical care and tell your healthcare provider about your travel history. Do not wait for a specific symptom — any fever within 21 days of returning from West Africa warrants evaluation and disclosure of travel history.
