A severe, Ebola-like illness native to West Afria is an unrecognized threat with global implications—and imported cases have already been detected in the U.S.—experts have warned.
The researchers have said that there is an urgent need for improved detection and treatment of Lassa fever, which causes thousands of deaths worldwide each year, most commonly in Nigeria, Liberia and Sierra Leone.
The disease is spread primarily by rodents, but can also be transmitted person-to-person through direct contact with the blood, body fluids, or secretions of those infected.
The World Health Organization has designated Lassa fever as being among the world’s top pandemic threats: more than 32 imported cases have been reported globally, including in the US. Of those, one-third proved fatal.
According to researchers, testing for the disease is limited even in areas where it is endemic, and many cases go undiagnosed.
The UNC Project-Liberia team has established real-time PCR testing for Lassa virus in rural Liberia, however doctors must have a clinical suspicion that Lassa fever is behind a patient’s illness before ordering a test, and the spectrum of symptoms is still not fully understood.
A medically-reviewed report from the Cleveland Clinic reports that while many people get mild symptoms of the virus, such as fever and headaches, around one in five people become seriously ill, with pregnant women in particular at high risk for dangerous complications and miscarriage.
Symptoms include fever, fatigue, cough, sore throat and headache, while severe symptoms can include pain, difficulty breathing, severe vomiting or diarrhea, seizures, confusion, and bleeding from the mouth, nose, and eyes.
The PREPARE study, led by researchers at the Institute for Global Health and Infectious Diseases at the University of North Carolina School of Medicine in Chapel Hill and published in The Lancet Infectious Diseases, warns that early detection is vital for preventing deaths from the disease.
“Many of these deaths can be prevented with early and increased access to diagnostics, supportive care and potentially initiation of effective therapeutics,” said Dr. William A Fischer II, who co-led the study with Dr. David Wohl. Both are co-directors of UNC Project-Liberia.
“Furthermore, with over 30 reported cases of Lassa fever imported into non-endemic countries, one third of which were fatal, the importance of early detection and care extends beyond West Africa.”
The PREPARE study, conducted between July 2018 and August 2024 at two hospitals in central Liberia, involved 435 patients aged five and older who were admitted with either clinical suspicion of Lassa fever, or with an illness involving a fever. All participants underwent PCR testing for Lassa fever, and those with confirmed infection were studied during their hospitalizations and up to a year after being discharged.
It found that 11 percent of patients admitted with a fever, though not suspected to have Lassa fever, were in fact diagnosed with the disease. Children between the ages of 5 to 17 were disproportionately affected, with 43 percent of confirmed cases.
Limited access to PCR testing, and overlapping symptoms with other common infectious diseases, contributed to underdiagnosis, and the patients who died had higher viral loads and weaker antibody responses.
“These findings reveal how easily cases slip through routine clinical screening,” professor of medicine Dr. Wohl said. “Our data make it clear that without widening our diagnostic aperture to look beyond routine diagnostic assumptions, a substantial number of Lassa virus infections will be missed.”
Missed diagnoses worsen patient outcomes, as well as exposing health care workers to infection and increasing the risk of human-to-human transmission, showing the importance of early detection and treatment for the disease, as the window for effective intervention is narrow.
“By detecting Lassa fever early, we can help those infected and also keep this dangerous pathogen from becoming a threat for those near and far,” Dr. Fischer said.
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References
Ochu, C. L., & Evans, W. D. (2026). Lassa viral dynamics: Implications for missed diagnosis. The Lancet Infectious Diseases. https://doi.org/10.1016/S1473-3099(25)00731-5
Wohl, D. A., Pewu, C., Lee, C., Kerkula, E., Gayflowu, M., Doetein, N., Mollan, K. R., Krajewski, T. J., Straub, B., Flomo, A., Fofana, A., Kerkula, S., Sumo, T., Sampson, A., Vouh, S., Flomo, F., Colt, M. A., Remont, T., Watts, E. R., … Fischer, W. A. (2026). Lassa fever symptomatology, viral dynamics, and host immune response (PREPARE): A prospective, observational cohort study in Liberia. The Lancet Infectious Diseases. https://doi.org/10.1016/S1473-3099(25)00725-X
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