Lassa fever is a life-threatening acute viral hemorrhagic fever (VHF) caused by the Lassa virus (LASV), a member of the arenavirus family. Estimates reveal that Lassa fever affects 2.7 million people annually and has no effective treatment for severe symptoms [1].
The death rate for those who are hospitalized with Lassa fever is quite high. The deadly virus causes severe bleeding in some cases, similar to Ebola, but lacks an available vaccine [1,2].
Lassa fever is rated as having the highest risk of a zoonotic spillover- transforming from an animal-borne virus to one that could spread quickly between humans [3].
Lassa fever is still largely unknown, probably because it has mostly been confined to parts of West Africa—until recently. As the virus began appearing in other areas, it got on the World Health Organization’s (WHO) R&D Blueprint list of diseases that need urgent research [4].
Another reason for caution is that Lassa virus symptoms can take time to appear. Many infected people don’t show symptoms at all [1]. This makes it easier for the virus to spread silently through global travel.
In 2024, a resident of the United States died from Lassa fever after returning from West Africa, putting the virus back into the spotlight [5].
Here, we explore the history, epidemiology, transmission, symptoms, diagnosis, treatment, and prevention of Lassa fever.
Lassa fever spreads primarily through contact with rodent urine and droppings. People often get infected by handling or eating contaminated food. The risk goes up if the virus enters open cuts or sores. Lassa fever is also transmitted through the blood and body fluids of infected individuals [6].
Even sweeping an area where rodents have been can pose a danger since inhaling contaminated air particles may lead to infection [6].
Lassa fever was initially described in the 1950s, but Lassa virus was first detected in 1969 when nurses working in Lassa, Nigeria, died from the infection. The Lassa virus was first isolated and identified by Dr. Jordi Casals, a virologist and epidemiologist known for discovering the virus [7].
The doctor almost risked his life in the process. While working with the virus in his laboratory at Yale University, Dr. Casals fell severely ill and nearly died. Fortunately, he received blood transfusions from a nurse who had previously survived a Lassa virus infection [7].
Until recently, experts estimated that 100,000-300,000 people were infected with Lassa fever [8]. However, a 2024 study differs. The estimated number of Lassa virus infections is 2.7 million [1].
Lassa fever is endemic to West Africa. In particular, it is found in:
Neighboring countries are also at risk [2,3].
People living in rodent-infested areas of West Africa face the highest risk of Lassa fever. Travelers to the region should also be mindful. The virus can infect people of all ages, including children.
Since the viral infection can spread through direct contact with the blood and body fluids of a person infected with Lassa virus, healthcare workers are at risk if they do not adhere to safety protocols and wear protective gear.
GIDEON gives you comprehensive information about Lassa fever outbreaks, cross-border events, clinical references, and more.
Most people with Lassa fever experience mild or no symptoms. However, severe cases lack effective treatment or a cure, and there’s no licensed vaccine. While the overall case-fatality rate is around 1%, it rises to 15% for those with severe symptoms who are hospitalized. 4 in 10 people with Lassa fever experience bleeding from the nose, mouth, or other areas [9].
Originally, the virus spread mainly through a specific rodent species in West Africa called the multimammate rat (Mastomys), but it has been detected in new rodent species. This raises concerns about the spread to more regions and, potentially, other vectors [6].
Although Lassa fever rarely spreads from person to person, it is rated as one of the most likely viruses to jump from animals to humans (zoonotic spillover) [3].
Early symptoms of Lassa fever are similar to those of other viral febrile infections. They include:
In a few days, symptoms may include:
80% of people with Lassa fever are estimated to have mild symptoms or no symptoms at all. However, in 20% of cases, severe symptoms may develop after 4-7 days, including:
Complications of Lassa fever include hearing loss, which can range from mild to severe. People who are pregnant are at a high risk of miscarriage. Deaths usually occur within 10-14 days from when symptoms start [9, 10].
Lassa fever incubation period is 6-21 days, according to the World Health Organization (WHO) [10].
Diagnosing Lassa fever can be challenging since early symptoms often resemble those of other viral hemorrhagic fevers and other infections. A confirmed diagnosis usually requires specialized labs, and handling the virus specimen requires caution [11].
Laboratory testing includes reverse transcriptase polymerase chain reaction (RT-PCR), antibody enzyme-linked immunosorbent assay (ELISA), and antigen tests [11].
Lassa fever is often misdiagnosed at point-of-care facilities because its symptoms are similar to those of other diseases like:
GIDEON’s differential diagnosis tool helps you confirm your diagnosis faster and with more accuracy.
Ribavirin, the only approved treatment for Lassa fever, is an antiviral that can reduce deaths by 90% if taken within six days of symptom onset [12].
Apart from intravenous Ribavirin, supportive care is provided to help the infected individual manage their symptoms [12].
Lassa fever spreads through rodents that thrive in areas with exposed food. Storing food in airtight, rodent-proof containers is a key preventive measure. Additionally, safe and sanitary garbage disposal, away from residential areas, and maintaining clean homes and communities can help reduce the risk of a Lassa fever infection [13].
Endemic regions face significant challenges due to limited healthcare infrastructure and access to quality care. Poverty leaves many people below the poverty line without adequate primary care facilities[13].
Additionally, many healthcare facilities lack adequate infection control measures, including sufficient supplies of protective gear to protect healthcare workers from contracting Lassa fever [13].
Investing in medical infrastructure, training for more doctors, nurses, and healthcare workers, and personal protective equipment (PPE) can help Lassa fever patients get the timely treatment they need [13].
Global travel has boomed, and travelers can spread the Lassa virus to new shores. Raising awareness at entry points and point-of-care facilities can help facilitate early accurate diagnoses. Collecting a patient’s recent travel information can help improve the accuracy of differential diagnosis, allowing for early and effective intervention [6].
Increased surveillance and robust reporting of Lassa fever outbreaks from endemic countries can also help curb transmission [6, 13].
There is no effective treatment after severe symptoms of Lassa fever develop. Additionally, there is no vaccine to help prevent Lassa virus infections. Apart from effective vaccines, public health agencies also need to invest in building vaccine acceptance in endemic countries to contain outbreaks [1].
Lassa fever is a serious public health threat, especially in West Africa. However, it is becoming a global concern. With no effective treatment for severe cases and no available vaccine, awareness and improved surveillance and case reporting are the best defense. Additionally, simple measures, like storing food securely and disposing of waste properly, can lower the presence of rodent vector populations in endemic high-risk regions.
Improving healthcare infrastructure and protective measures for healthcare workers is the need of the hour. As global travel increases, so does the risk of spread, making early diagnosis and rapid response essential. Continued research and investment are urgently needed to tackle Lassa fever and reduce its impact worldwide.
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| [1] | D. R. M. Smith et al., “Health and economic impacts of Lassa vaccination campaigns in West Africa,” Nat. Med., 2024. |
| [2] | D. Simons, “Lassa fever cases suffer from severe underreporting based on reported fatalities,” Int. Health, vol. 15, no. 5, pp. 608–610, 2023. |
| [3] | Z. L. Grange et al., “Ranking the risk of animal-to-human spillover for newly discovered viruses,” Proc. Natl. Acad. Sci. U. S. A., vol. 118, no. 15, 2021. |
| [4] | “R&D blue print and Ebola/Marburg,” Who.int. [Online]. Available: https://www.who.int/teams/blueprint/lassa-fever. [Accessed: 07-Nov-2024]. |
| [5] | CDC, “Lassa fever suspected in death of U.s. traveler returning from West Africa,” CDC Newsroom, 01-Nov-2024. [Online]. Available: https://www.cdc.gov/media/releases/2024/s1028-lassa-fever.html. [Accessed: 07-Nov-2024]. |
| [6] | J. K. Richmond, “Lassa fever: epidemiology, clinical features, and social consequences,” BMJ, vol. 327, no. 7426, pp. 1271–1275, 2003. |
| [7] | “Lassa Fever,” Africa CDC, 03-Sep-2019. [Online]. Available: https://africacdc.org/disease/lassa-fever/. [Accessed: 07-Nov-2024]. |
| [8] | “Global Infectious Diseases and epidemiology network,” GIDEON, 28-Jun-2021. [Online]. Available: http://www.gideononline.com. [Accessed: 07-Nov-2024]. |
| [9] | E. Dwalu et al., “Trend of Lassa fever cases and factors associated with mortality in Liberia, 2016 – 2021: a secondary data analysis,” Pan Afr. Med. J., vol. 47, 2024. |
| [10] | “Lassa fever,” Who.int. [Online]. Available: https://www.who.int/news-room/fact-sheets/detail/lassa-fever. [Accessed: 07-Nov-2024]. |
| [11] | A. N. Happi, C. T. Happi, and R. J. Schoepp, “Lassa fever diagnostics: past, present, and future,” Curr. Opin. Virol., vol. 37, pp. 132–138, 2019. |
| [12] | Q. O. Lawal, J. Okoeguale, S. O. Oiwoh, T. Akhigbe, R. A. Eifediyi, and S. A. Okogbenin, “Addressing bottlenecks in Lassa fever treatment: overcoming the ribavirin parenteral formulation challenge,” Trop. Med. Health, vol. 52, no. 1, 2024. |
| [13] | R. F. Garry, “Lassa fever — the road ahead,” Nat. Rev. Microbiol., vol. 21, no. 2, pp. 87–96, 2023. |