Lassa Fever: Causes, Symptoms, and Management
Updated: 2 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026
Lassa fever is a viral hemorrhagic illness common in West Africa, primarily spread through contact with infected multimammate rats or their waste. While 80% of cases are mild, it can lead to severe complications like hearing loss, organ failure, and high fetal loss in pregnant women. Management involves antiviral medication and strict isolation to prevent further transmission.
Quick Answer: What is Lassa fever?
Lassa fever is a viral hemorrhagic fever caused by the Lassa virus, endemic to several West African nations and spread mainly through contact with infected Mastomys rats' urine or feces or infected people's body fluids. Most cases are mild, but approximately 20% become severe, and hearing loss affects one-third of patients. Treatment involves ribavirin and supportive care. [1]
What the research says
Lassa fever carries about a threefold higher risk of death in pregnancy. A systematic review and meta-analysis of 13 studies estimated the absolute risk of maternal death at 33.73% (95% CI 22.05 to 46.42%) and the relative risk of death in pregnant compared with non-pregnant women at 2.86 (95% CI 1.77 to 4.63) (Kayem et al., Trans R Soc Trop Med Hyg, 2020 [2]).
The evidence for ribavirin is limited. A systematic review that included 6 studies found that the evidence mostly relies on a single prospective trial with critical risk of bias; in that trial, mortality was lower with ribavirin in patients with elevated aspartate aminotransferase (OR 0.41, 95% CI 0.23 to 0.73) but higher in patients without elevated levels (OR 2.37, 95% CI 1.07 to 5.25) (Eberhardt et al., Int J Infect Dis, 2019 [3]).
Hearing loss is the most common long-term problem in survivors. A scoping review of 9 studies found that hearing loss was the most prevalent sequela, affecting 16 to 35% of survivors, and was often bilateral and sensorineural (Saka et al., BMC Infect Dis, 2025 [4]).
What is Lassa Fever?
Lassa fever is a significant viral hemorrhagic fever (VHF) prevalent in several West African countries, including Nigeria, Liberia, and Sierra Leone [1]. It is caused by the Lassa virus, which belongs to a group of viruses capable of damaging blood vessels and interfering with the body's natural clotting mechanisms. Annually, between 100,000 and 300,000 infections occur in the region, though it remains extremely rare outside of these endemic areas.
The virus is primarily carried by the Mastomys rat, also known as the multimammate rat. Humans typically become infected through direct or indirect contact with rodent waste that contaminates food, water, or household surfaces. Once a human is infected, the virus can also spread through direct contact with their blood, urine, or other body fluids, making strict clinical isolation essential in healthcare settings.
How Lassa virus reaches people: infected Mastomys rats contaminate food and household items, and infected people can then pass the virus on through body fluids.
What are the symptoms of Lassa fever, and how severe can it be?
The majority of Lassa fever cases—approximately 80%—present with mild symptoms that can be easily mistaken for other common tropical illnesses [1]. However, the remaining 20% of patients develop severe, life-threatening symptoms that require immediate medical attention.
Severity Level | Common Symptoms |
|---|---|
Mild (80%) | Fever, general fatigue, dry cough, sore throat, and headache. |
Severe (20%) | Chest and abdominal pain, respiratory distress, severe vomiting, and seizures. |
Critical Signs | Hemorrhaging from the eyes, nose, or mouth, and profound confusion. |
A unique and frequent complication of Lassa fever is hearing loss. Roughly one in three patients will experience partial or complete deafness, regardless of the initial severity of their infection. While about half of these individuals may regain their hearing within a few weeks, for many, the loss is permanent.
Hearing loss affects roughly one in three people with Lassa fever, whether the illness was mild or severe.
What are the risks of Lassa fever during pregnancy?
Pregnant women are at an exceptionally high risk when infected with the Lassa virus [1]. The mortality rate for pregnant women is approximately 33%, significantly higher than the 1% mortality rate seen in the general population. Furthermore, fetal loss occurs in more than 75% of pregnancies where the mother is infected.
Clinical management for pregnant patients requires immediate antiviral treatment and intensive monitoring. In cases of miscarriage, medical providers must prioritize the removal of fetal tissue to improve the mother's chances of recovery. In later stages of pregnancy, early delivery may be recommended to safeguard the health of both the mother and the infant.
How is Lassa fever diagnosed and treated?
Diagnosing Lassa fever is challenging because its early symptoms closely resemble those of malaria, dengue fever, and Ebola. Healthcare providers rely on specialized laboratory tests, including blood work, throat swabs, and urinalysis, to detect the presence of the Lassa virus. Providing a detailed travel history is crucial for an accurate and timely diagnosis.
The primary medical treatment for Lassa fever is the antiviral medication ribavirin [1]. Supportive care is also vital for managing severe complications and may include:
Supplemental Oxygen: To assist patients experiencing acute respiratory distress.
Intravenous Fluids: To maintain hydration and correct electrolyte imbalances.
Dialysis: Required for patients who develop sudden kidney failure.
How can Lassa fever be prevented, and what is the outlook?
Preventing Lassa fever focuses on reducing human contact with infected rodents. This includes maintaining clean living environments, storing food in rodent-proof containers, and discouraging rats from entering homes. In healthcare settings, the use of personal protective equipment (PPE)—such as masks, gloves, and gowns—is mandatory to prevent human-to-human transmission.
Healthcare workers use protective equipment such as masks, gloves, and gowns to prevent human-to-human spread of Lassa virus.
While the overall survival rate is high due to the prevalence of mild cases, the mortality rate increases to 15% for those who require hospitalization. Early detection and the prompt administration of antiviral therapy remain the most effective strategies for improving patient outcomes and reducing the long-term impact of the disease.
Conclusion
Lassa fever remains a serious public health challenge in West Africa, characterized by its complex transmission and potential for severe complications. Understanding the risks, particularly for pregnant women and the high incidence of hearing loss, is essential for both residents and travelers. Through improved sanitation, rodent control, and early medical intervention, the impact of this viral illness can be significantly mitigated.
Professional Consultation and Support
If you have recently traveled to West Africa and are experiencing symptoms like fever, fatigue, or unexplained bleeding, seek medical care immediately at a facility equipped to handle viral hemorrhagic fevers. Early intervention is critical for managing the disease and preventing its spread to others.
Frequently Asked Questions
How do people get Lassa fever?
Most people are infected through contact with the waste of infected Mastomys rats, which can contaminate food or household items. It can also spread through contact with the body fluids of an infected person. [1]
Is Lassa fever common in the United States?
No, there have been no reports of individuals becoming infected with Lassa fever within the United States. It is primarily found in West African countries.
What are the mild symptoms of Lassa fever?
About 80% of cases involve mild symptoms such as fever, tiredness, cough, sore throat, and headache.
Can Lassa fever cause permanent hearing loss?
Yes. Approximately one-third of all patients experience some degree of hearing loss, which can be permanent in about half of those affected.
Why is Lassa fever dangerous during pregnancy?
Lassa fever carries a high mortality rate for the mother (33%) and results in fetal loss in over 75% of cases.
What is the mortality rate of Lassa fever?
The overall mortality rate is about 1%, but it rises to 15% for hospitalized patients and 33% for pregnant women.
How is Lassa fever treated?
The primary treatment is the antiviral drug ribavirin, along with supportive care like IV fluids and supplemental oxygen.
Can Lassa fever be prevented?
Yes, by keeping living areas free of rodents, storing food in closed containers, and using proper PPE when caring for infected individuals.
Is Lassa fever contagious between humans?
Yes, it can spread through direct contact with an infected person's blood, urine, feces, or other body fluids. The virus can stay in semen for months after recovery, so survivors should use condoms or avoid sex as advised by their doctor.
How long does it take to recover from Lassa fever?
Mild cases typically take a week or longer to resolve. Recovery from severe complications like hearing loss may take several weeks.
Related Reading
Hantavirus Pulmonary Syndrome: What It Is, Why It Happens, and How It's Treated explains another serious viral illness spread by rodents.
What is Yellow Fever? covers a viral fever found in Africa and South America.
Hearing Loss: Symptoms, Causes, and Treatment Options explains hearing loss, a known complication of Lassa fever, and its treatment.
What Is Malaria? The Mosquito-Borne Disease That Still Infects Hundreds of Millions covers a common cause of fever in travelers to West Africa.
References
Cleveland Clinic. Lassa Fever. Cleveland Clinic. June 20, 2023. https://my.clevelandclinic.org/health/diseases/25095-lassa-fever
Kayem ND, Benson C, Aye CYL, et al. Lassa fever in pregnancy: a systematic review and meta-analysis. Trans R Soc Trop Med Hyg. 2020;114(5):385-396. PMID: 32125412. DOI: https://doi.org/10.1093/trstmh/traa011
Eberhardt KA, Mischlinger J, Jordan S, et al. Ribavirin for the treatment of Lassa fever: a systematic review and meta-analysis. Int J Infect Dis. 2019;87:15-20. PMID: 31357056. DOI: https://doi.org/10.1016/j.ijid.2019.07.015
Saka SA, Lawal QO, Otaigbe O, et al. Lassa fever survivors: long-term health effects and chronic sequelae - a scoping review. BMC Infect Dis. 2025;25(1):823. PMID: 40597771. DOI: https://doi.org/10.1186/s12879-025-11262-1
Medical disclaimer
This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. The clinical information in this guide reflects source material last reviewed in June 2023.
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