Lassa Fever Symptoms In Adults

  • Batoul SalamahBachelor’s degree in Pharmacy from Damascus University\Syria

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We are always exposed to numerous types of diseases and disorders; some of them might be simple and easily curable, and some are severe and dangerous. On the other hand, some of these illnesses can be simple and severe at the same time, and that can’t be determined because each case has its own situation.

What is Lassa fever?

  • Lassa fever (LF) is an acute viral hemorrhagic disease that is caused by the Lassa virus. LF is endemic in parts of West Africa, including Guinea, Nigeria, Sierra Leone, and Liberia. Lassa fever is a seasonal illness, and it’s estimated to cause 100.000--300.000 new cases and 5.000 deaths every year.1
  • This disease was first described in the 1950s, and the virus was identified in 1969 after the deaths of two nurses in the Nigerian town of Lassa, and Lassa virus is one of the arenavirus family.

Lassa fever causes

  • Human beings get infected with the Lassa virus through transmission from contacting the excreta of infected rodents (mostly the Mastomys rat), handling or consumption of contaminated food or household items (mostly how children and people who stay or work at home get infected), or through direct contact with the bodily fluids of an infected person (like health care workers).1
  • Usually, transmission to close contacts (from one person to another) happens only when the patient has symptoms. The patient can, however, excrete the virus in the urine for 3--9 weeks after the onset of the disease and via semen for up to 3 months.

Lassa fever symptoms in adults

Several studies were conducted to examine the signs and symptoms of Lassa fever.

  • One study was conducted to examine all the characteristics of Lassa fever; it included several studies and research reports with high numbers of patients. At baseline clinical assessment, fever was the most reported symptom in 88% of patients (1527/1730 individuals), followed by headache in 50% of patients (809/1622 individuals), vomiting in 49% of patients (806/1613 individuals), abdominal pain in 42% of patients (660/1581 individuals), and cough in 35% of patients (556/1581 individuals). Another smaller group of patients had more serious or life-threatening symptoms, such as breathing difficulty in 7% of patients (21/310 individuals), shock in 6% of patients (12/187 individuals), and seizures in 3% of patients (13/517 individuals). Labour complications were reported in 29% of pregnant women (2/7 individuals).1
  • In the assessment of post-baseline clinical characteristics, fever was again the most prevalent symptom in 93% of patients (3067/3300 individuals), followed by headache in 64% of patients (2033/3200 individuals), vomiting in 55% of patients (1695/3077 individuals), and abdominal pain in 52% of patients (1594/3039 individuals). Severe and life-threatening signs increased as well; shock increased the most among the others, followed by breathing difficulty and seizures, and among the 6373 individuals, 1896 died (30%). Bleeding was a significant symptom that was present in both baseline (14%) and post-baseline (12%) characteristics and the most reported type of bleeding was haematuria (blood in the urine).1
  • Another study was applied to monitor the symptoms of 34 patients. Of them, fever was present in 32 patients (94.1%), 14 patients (60.9%) suffered from pharyngitis, and 12 patients (50%) had central nervous system (CNS) involvement. Out of 18 cases, abdominal pain was found in 11 patients (61.1%) and chest pain in 8 patients (44.4%). Rash and cervical lymphadenitis were reported in 5 out of 19 cases (26.3%). Haemorrhage was present in five out of 23 patients (21.7%), and proteinuria was reported in 7 out of 9 cases (77.8%). Another significant symptom well described, which is hypoacusis, was reported in 6 out of 16 patients (37.5%).2
  • One of the most serious and dangerous manifestations of Lassa fever is hearing loss. Many studies have been conducted to understand this symptom and why it occurs. It has been estimated that approximately a third of Lassa fever survivors develop unilateral or bilateral sudden-onset sensorineural hearing loss (SNHL), and only some of those fully recover. SNHL is defined as damage to the inner ear nerve or the cochlear hair cells. There have been several theories about the pathophysiology of SNHL and how it develops in Lassa fever patients, and they ended with two suggestions: the development of SNHL during the acute phase of the illness (when the virus is actively replicating) suggests that direct viral damage is the mechanism; on the other hand, the convalescent-stage onset of symptoms is likely to be associated with an immune-mediated complication.3
  • There have been other neurological complications associated with Lassa fever, such as ataxia and acute or chronic neuropsychiatric syndromes, but at a much lower rate. Understanding the pathophysiology of these neurological signs would probably aid in understanding the mechanism of SNHL associated with Lassa fever.3
  • Lassa fever outcomes in pregnant women: In one of the studies conducted to observe Lassa fever complications in pregnant women, 30 pregnant women with Lassa fever have been completely monitored. Of these thirty, 16 patients had complications that included convulsions, irrational behaviours, coma, extravaginal bleeding, and oliguria. All these sixteen women were found to have had an intrauterine fatal death or an abortive process as well. Ten of these 16 cases (58.8%) died within 24-48 hours before the completion of the uterine evacuation. The other 14 women suffered from mild symptoms like fever, malaise, sore throat, and cough, and only one foetus of these fourteen died. Overall, 11 women of these 30 died and 19 survived (the mortality rate is 36.7%). If we divide the mortality rate according to the trimesters, it would be 50% (5/10 patients) in the first, 75% (3/4 patients) in the second, and 18.7% (3/16 patients) in the third. Regarding the foetuses, 17/31 (56.7%) of them died (one woman was pregnant with twins, one of them died, and the other one survived). The mortality rate of the foetuses was significantly higher when the mother was admitted to the hospital in the first and second trimesters, with a rate of 92.9% (13/14 patients) compared with 31.2% (6/17 patients) for the third trimester.4
  • Generally, Lassa fever is asymptomatic or mild in 80% of cases. The incubation period is usually between seven and ten days, with a maximum of twenty-one days. Regarding the children, their symptoms are similar to those of adults. Infant infections, however, can result in swollen baby syndrome, which causes abdominal distension, oedema, bleeding, and often death.

Lassa fever complications

Patients with Lassa fever can develop other severe complications, such as:

  • Pericarditis (when the lining around your heart gets inflamed)
  • Hepatitis
  • Sudden kidney failure
  • Acute respiratory distress syndrome (ARDS), can prevent your body from getting enough oxygen
  • Pleural effusion (fluid around your lungs)
  • Disseminated intravascular coagulation (severe blood clotting disorder)
  • Sepsis, which is a severe reaction to an infection

Lassa fever diagnosis

The problem in diagnosing Lassa fever is the need for high containment facilities for diagnostics and assay development validation. Moreover, diagnostic testing is probably limited in endemic areas due to shortages in resources, in addition to the co-infection of other diseases like malaria, which can interfere with the diagnosing process. Anyway, virus culture is historically considered the ‘gold standard’ for diagnosing Lassa fever. There are, however, other diagnostic laboratory methods to diagnose Lassa fever.5

Lassa fever treatment

  • Treating Lassa fever depends mainly on antiviral therapy, especially ribavirin, along with supportive care therapy. Recently, there has been a new antiviral drug, which is favipiravir, that has been used with ribavirin and has proven to be more effective this way.5
  • There has been no vaccination until now, but there have been significant improvements in developing it.5

Lassa fever prevention

You can protect yourself and lower the risk of Lassa fever by following these steps:

  • Avoid any contact with rodents, especially in endemic areas
  • Wear protective clothes when taking care of Lassa fever patients
  • Stay away from people if you’re infected with Lassa fever


Lassa fever is a serious disease that causes severe symptoms and complications. Although most of the cases are asymptomatic and don’t cause any permanent harm, some of the cases can develop to be severe and cause death sometimes. Unfortunately, there has been no vaccination for this disease until now, but there are promising results about a potential one; therefore, the best prevention is to protect yourself from getting infected as much as possible by staying away from rodents and ill people.


  1. Merson L, Bourner J, Jalloh S, Erber A, Salam AP, Flahault A, et al. Clinical characterization of Lassa fever: A systematic review of clinical reports and research to inform clinical trial design. Schibler M, editor. PLoS Negl Trop Dis [Internet]. 2021 Sep 21 [cited 2024 Feb 17];15(9):e0009788. Available from:
  2. Wolf T, Ellwanger R, Goetsch U, Wetzstein N, Gottschalk R. Fifty years of imported Lassa fever: a systematic review of primary and secondary cases. Journal of Travel Medicine [Internet]. 2020 Jul 14 [cited 2024 Feb 17];27(4):taaa035. Available from:
  3. Mateer EJ, Huang C, Shehu NY, Paessler S. Lassa fever–induced sensorineural hearing loss: A neglected public health and social burden. Rabaa MA, editor. PLoS Negl Trop Dis [Internet]. 2018 Feb 22 [cited 2024 Feb 17];12(2):e0006187. Available from:
  4. Okogbenin S, Okoeguale J, Akpede G, Colubri A, Barnes KG, Mehta S, et al. Retrospective cohort study of lassa fever in pregnancy, southern nigeria. Emerg Infect Dis [Internet]. 2019 Aug [cited 2024 Feb 17];25(8):1494–500. Available from:
  5. Garnett LE, Strong JE. Lassa fever: With 50 years of study, hundreds of thousands of patients and an extremely high disease burden, what have we learned? Current Opinion in Virology [Internet]. 2019 Aug [cited 2024 Feb 17];37:123–31. Available from:

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This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Batoul Salamah

Bachelor’s degree in Pharmacy from Damascus University\Syria
Associate’s degree in Health Sciences from the University Of the People\United States

Batoul has significant expertise in various domains of pharmacy. For instance, she worked in several community pharmacies, where she worked directly with patients. She worked as a senior pharmaceutical representative as well, where she worked directly with doctors and physicians. And currently, she’s working as a freelance medical writer, where she puts her humble expertise into helping people get the correct information about their health and how to take care of it.

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