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Lassa fever is a type of viral hemorrhagic fever caused by the Lassa virus.[1] Many, but not all, of those infected by the virus do not develop symptoms.[1] The disease is usually first spread to people via contact with the urine or feces of an infected multimammate mouse;[1] there is currently no vaccine available.[2]

Signs and symptoms

Onset of symptoms is typically 7 to 21 days after exposure.[3][3][4] These symptoms may include fever, tiredness, weakness, and headache.[3] In 20 percent of people more severe symptoms such as bleeding gums, breathing problems, vomiting, chest pain, or very low blood pressure may occur.[3]


Lassa viruses are enveloped, single-stranded, bisegmented, ambisense RNA viruses.[5][6] Their genome is contained in two RNA segments that code for two proteins each, one in each sense, for a total of four viral proteins.[7][8]


Lassa virus commonly spreads to humans from other animals, specifically the natal multimammate mouse or African rat, also called the natal multimammate rat, Mastomys natalensis.[9] One of the most common mouse in equatorial Africa, common in human households and eaten as a delicacy in some areas.[9][10]


In terms of the mechanism of Lassa fever, currently the chain of events that occur during disease development is not known.[11] However, according to one review in 2012, a possible pathogenesis could be infection-triggered induction of uncontrolled cytokine expression. According to the same review the hypothesis would be supported by a case in which - proinflammatory cytokines, interferon (gamma) and tumor necrosis factor (alpha) all rose to very high levels before death of an infected individual with the virus.[11]


The evaluation of this infection is done by enzyme-linked immunosorbent serologic assays, which detect certain antibodies; RT-PCR can be used as well to detect the disease.[12] In cases with abdominal pain, in countries where Lassa is common, Lassa fever is often misdiagnosed as appendicitis and intussusception which delays treatment.[13]


Treatment is directed at addressing dehydration and improving symptoms,[1] all persons suspected of Lassa fever infection should be admitted to isolation facilities and their body fluids and excreta properly disposed of. The antiviral medication ribavirin has been recommended,[1] but evidence to support its use is weak.[14]


About 15 to 20 percent of hospitalized people with Lassa fever will die from the illness. The overall case fatality rate is estimated to be 1 percent, but during epidemics, mortality can climb as high as 50 percent.[15]

Epidemiology 1

Lassa high risk areas are near the western and eastern extremes of West Africa. As of 2018, the Lassa belt includes Guinea, Nigeria, Sierra Leone and Liberia.[16] As of 2003, 10 to 16 percent of people in Sierra Leone and Liberia admitted to the hospital had the virus.[9] The case fatality rate for those who are hospitalized for the disease is about 13 percent. [17]

Epidemiology 2

An outbreak of Lassa fever occurred in Nigeria during 2018 and spread to 18 of the country's states; it was the largest outbreak of Lassa fever recorded.[18][19][20] On 25 February 2018, there were 1081 suspected cases and 90 reported deaths; 317 of the cases and 72 deaths were confirmed as Lassa which increased to a total of 431 reported cases later in 2018.[21]


  1. 1.0 1.1 1.2 1.3 1.4 "Lassa fever". Retrieved 20 April 2022.
  2. Yun, N. E.; Walker, D. H. (2012). "Pathogenesis of Lassa Fever". Viruses. 4 (12): 2031–2048. doi:10.3390/v4102031. PMC 3497040. PMID 23202452.
  3. 3.0 3.1 3.2 3.3 "Signs and Symptoms | Lassa Fever | CDC". 6 March 2019. Archived from the original on 9 July 2017. Retrieved 18 June 2019.
  4. Greenky D, Knust B, Dziuban EJ (May 2018). "What Pediatricians Should Know About Lassa Virus". JAMA Pediatrics. 172 (5): 407–408. doi:10.1001/jamapediatrics.2017.5223. PMC 5970952. PMID 29507948.
  5. Jamie Dyal and Ben Fohner Lassa virus Archived 25 March 2013 at the Wayback Machine Stanford University Humans and Viruses Class of 2005, n.d. accessed 9 May 2018
  6. Lashley, Felissa R., and Jerry D. Durham. Emerging Infectious Diseases: Trends and Issues. New York: Springer Pub., 2002. Print.
  7. Ridley, Matt. Genome: The Autobiography of a Species in 23 Chapters. New York: HarperCollins, 1999. Print.
  8. "Lassa virus RefSeq Genome". Archived from the original on 17 July 2018. Retrieved 20 April 2022.
  9. 9.0 9.1 9.2 Richmond, J. K.; Baglole, D. J. (2003). "Lassa fever: Epidemiology, clinical features, and social consequences". BMJ. 327 (7426): 1271–1275. doi:10.1136/bmj.327.7426.1271. PMC 286250. PMID 14644972.
  10. Werner, Dietrich (2004). Biological Resources and Migration. Springer. pp. 363. ISBN 978-3-540-21470-0.
  11. 11.0 11.1 Yun, Nadezhda E.; Walker, David H. (9 October 2012). "Pathogenesis of Lassa Fever". Viruses. 4 (10): 2031–2048. doi:10.3390/v4102031. ISSN 1999-4915. Archived from the original on 15 March 2022. Retrieved 22 April 2022.
  12. "Diagnosis | Lassa Fever | CDC". 4 March 2019. Retrieved 25 April 2022.
  13. Dongo, A. E.; Kesieme, E. B.; Iyamu, C. E.; Okokhere, P. O.; Akhuemokhan, O. C.; Akpede, G. O. (2013). "Lassa fever presenting as acute abdomen: a case series". Virology Journal. 10: 124. doi:10.1186/1743-422X-10-123. PMC 3639802. PMID 23597024.
  14. Eberhardt, Kirsten Alexandra; Mischlinger, Johannes; Jordan, Sabine; Groger, Mirjam; Günther, Stephan; Ramharter, Michael (1 October 2019). "Ribavirin for the treatment of Lassa fever: A systematic review and meta-analysis". International Journal of Infectious Diseases. 87: 15–20. doi:10.1016/j.ijid.2019.07.015. ISSN 1201-9712. Retrieved 26 April 2022.
  15. Centers for Disease Control and Prevention, "Lassa Fever, Signs and Symptoms" Archived 9 July 2017 at the Wayback Machine
  16. David Greenky, Barbara Knust, Eric J. DziubanWhat Pediatricians Should Know About Lassa Virus. JAMA Pediatr. 2018;172(5):407-408. doi:10.1001/jamapediatrics.2017.5223
  17. "Acute and Delayed Deaths after West Nile Virus Infection, Texas, USA, 2002–2012". CDC. CDC. Archived from the original on 3 February 2022. Retrieved 23 April 2022.
  18. Maxmen, Amy (15 March 2018). "Deadly Lassa-fever outbreak tests Nigeria's revamped health agency". Nature. 555 (7697): 421–422. Bibcode:2018Natur.555..421M. doi:10.1038/d41586-018-03171-y. PMID 29565399.
  19. "On the frontlines of the fight against Lassa fever in Nigeria". World Health Organization. March 2018. Archived from the original on 20 March 2018. Retrieved 20 March 2018.
  20. Beaubien, Jason (19 March 2018). "Nigeria Faces Mystifying Spike in Deadly Lassa Fever". NPR. Archived from the original on 19 March 2018. Retrieved 20 March 2018.
  21. "Lassa Fever – Nigeria". World Health Organization. 1 March 2018. Archived from the original on 6 March 2018. Retrieved 12 March 2018.