Official reprint from UpToDate®
www.uptodate.com ©2016 UpToDate®

Lassa fever

John S Schieffelin, MD, MSPH
Section Editor
Martin S Hirsch, MD
Deputy Editor
Elinor L Baron, MD, DTMH


Lassa fever is a hemorrhagic illness caused by Lassa virus [1-3]. Lassa fever was first recognized in Lassa, Nigeria, in 1969 and is endemic to West Africa; there are approximately 300,000 cases and 5000 deaths annually [4-12]. The animal reservoir is the rodent "multimammate rat" (Mastomys natalensis); transmission to humans occurs via contact with infected rodent urine and feces and via person-to-person contact [4,13]. Lassa virus is a single-stranded RNA virus belonging to the Arenaviridae family and has been classified as a category A bioterrorism agent [14].

Issues specific to Lassa fever will be reviewed here. Issues related to other causes of viral hemorrhagic fever are discussed separately. (See related topics.)


Geography — Lassa fever is endemic in parts of West African including Guinea, Liberia, Sierra Leone, Nigeria, Benin, Ghana, and Mali [15,16]; other neighboring countries are also at risk as the animal vector is distributed throughout the region. Cases have been reported in Côte d’Ivoire and Burkina Faso, and there is serologic evidence of Lassa virus infection among individuals in Togo [17-26].

The prevalence of Lassa virus infections varies within endemic areas; the incidence is highest in the forested regions of West Africa where Guinea, Liberia, and Sierra Leone share a border [17,27]. Within Sierra Leone, seroprevalence rates vary from 8 percent in coastal regions to 52 percent in the Eastern Province [4]. In Guinea, the seroprevalence rate varies from 4 to 55 percent [27-30].

Cases of Lassa fever occur at all times of year; the peak incidence occurs in March, during the transition from dry to wet season [5,31]. In addition, there is a smaller increase in incidence in December, during the middle of the dry season [31].


Subscribers log in here

To continue reading this article, you must log in with your personal, hospital, or group practice subscription. For more information or to purchase a personal subscription, click below on the option that best describes you:
Literature review current through: Sep 2016. | This topic last updated: Sep 14, 2016.
The content on the UpToDate website is not intended nor recommended as a substitute for medical advice, diagnosis, or treatment. Always seek the advice of your own physician or other qualified health care professional regarding any medical questions or conditions. The use of this website is governed by the UpToDate Terms of Use ©2016 UpToDate, Inc.
  1. Bowen MD, Rollin PE, Ksiazek TG, et al. Genetic diversity among Lassa virus strains. J Virol 2000; 74:6992.
  2. Vieth S, Torda AE, Asper M, et al. Sequence analysis of L RNA of Lassa virus. Virology 2004; 318:153.
  3. Sevilla N, de la Torre JC. Arenavirus diversity and evolution: quasispecies in vivo. Curr Top Microbiol Immunol 2006; 299:315.
  4. McCormick JB, Webb PA, Krebs JW, et al. A prospective study of the epidemiology and ecology of Lassa fever. J Infect Dis 1987; 155:437.
  5. Richmond JK, Baglole DJ. Lassa fever: epidemiology, clinical features, and social consequences. BMJ 2003; 327:1271.
  6. Frame JD, Baldwin JM Jr, Gocke DJ, Troup JM. Lassa fever, a new virus disease of man from West Africa. I. Clinical description and pathological findings. Am J Trop Med Hyg 1970; 19:670.
  7. Troup JM, White HA, Fom AL, Carey DE. An outbreak of Lassa fever on the Jos plateau, Nigeria, in January-February 1970. A preliminary report. Am J Trop Med Hyg 1970; 19:695.
  8. Leifer E, Gocke DJ, Bourne H. Lassa fever, a new virus disease of man from West Africa. II. Report of a laboratory-acquired infection treated with plasma from a person recently recovered from the disease. Am J Trop Med Hyg 1970; 19:677.
  9. Buckley SM, Casals J, Downs WG. Isolation and antigenic characterization of Lassa virus. Nature 1970; 227:174.
  10. White HA. Lassa fever. A study of 23 hospital cases. Trans R Soc Trop Med Hyg 1972; 66:390.
  11. Carey DE, Kemp GE, White HA, et al. Lassa fever. Epidemiological aspects of the 1970 epidemic, Jos, Nigeria. Trans R Soc Trop Med Hyg 1972; 66:402.
  12. Bowen GS, Tomori O, Wulff H, et al. Lassa fever in Onitsha, East Central State, Nigeria in 1974. Bull World Health Organ 1975; 52:599.
  13. Monath TP, Newhouse VF, Kemp GE, et al. Lassa virus isolation from Mastomys natalensis rodents during an epidemic in Sierra Leone. Science 1974; 185:263.
  14. Darling RG, Catlett CL, Huebner KD, Jarrett DG. Threats in bioterrorism. I: CDC category A agents. Emerg Med Clin North Am 2002; 20:273.
  15. Monath TP, Casals J. Diagnosis of Lassa fever and the isolation and management of patients. Bull World Health Organ 1975; 52:707.
  16. Ogbu O, Ajuluchukwu E, Uneke CJ. Lassa fever in West African sub-region: an overview. J Vector Borne Dis 2007; 44:1.
  17. Fichet-Calvet E, Rogers DJ. Risk maps of Lassa fever in West Africa. PLoS Negl Trop Dis 2009; 3:e388.
  18. Günther S, Emmerich P, Laue T, et al. Imported lassa fever in Germany: molecular characterization of a new lassa virus strain. Emerg Infect Dis 2000; 6:466.
  19. Dzotsi EK, Ohene SA, Asiedu-Bekoe F, et al. The first cases of Lassa fever in Ghana. Ghana Med J 2012; 46:166.
  20. Atkin S, Anaraki S, Gothard P, et al. The first case of Lassa fever imported from Mali to the United Kingdom, February 2009. Euro Surveill 2009; 14.
  21. Safronetz D, Lopez JE, Sogoba N, et al. Detection of Lassa virus, Mali. Emerg Infect Dis 2010; 16:1123.
  22. Safronetz D, Sogoba N, Lopez JE, et al. Geographic distribution and genetic characterization of Lassa virus in sub-Saharan Mali. PLoS Negl Trop Dis 2013; 7:e2582.
  23. Sogoba N, Rosenke K, Adjemian J, et al. Lassa Virus Seroprevalence in Sibirilia Commune, Bougouni District, Southern Mali. Emerg Infect Dis 2016; 22:657.
  24. ProMED-mail. Lassa fever - West Africa (16): Germany (North Rhine-Westphalia) local transmission 2016. http://www.promedmail.org/ (Accessed on March 29, 2016).
  25. ProMED-mail. Lassa Fever, Imported - Germany Ex West Africa (05) 2000. http://www.promedmail.org/ (Accessed on March 29, 2016).
  26. World Health Organization. WHO Disease Outbreak News. http://www.who.int/csr/don/19-february-2016-lassa-fever-benin/en/ (Accessed on February 29, 2016).
  27. Bausch DG, Demby AH, Coulibaly M, et al. Lassa fever in Guinea: I. Epidemiology of human disease and clinical observations. Vector Borne Zoonotic Dis 2001; 1:269.
  28. Kernéis S, Koivogui L, Magassouba N, et al. Prevalence and risk factors of Lassa seropositivity in inhabitants of the forest region of Guinea: a cross-sectional study. PLoS Negl Trop Dis 2009; 3:e548.
  29. Klempa B, Koulemou K, Auste B, et al. Seroepidemiological study reveals regional co-occurrence of Lassa- and Hantavirus antibodies in Upper Guinea, West Africa. Trop Med Int Health 2013; 18:366.
  30. Lukashevich IS, Clegg JC, Sidibe K. Lassa virus activity in Guinea: distribution of human antiviral antibody defined using enzyme-linked immunosorbent assay with recombinant antigen. J Med Virol 1993; 40:210.
  31. Shaffer JG, Grant DS, Schieffelin JS, et al. Lassa fever in post-conflict sierra leone. PLoS Negl Trop Dis 2014; 8:e2748.
  32. McCormick JB, King IJ, Webb PA, et al. A case-control study of the clinical diagnosis and course of Lassa fever. J Infect Dis 1987; 155:445.
  33. Bonner PC, Schmidt WP, Belmain SR, et al. Poor housing quality increases risk of rodent infestation and Lassa fever in refugee camps of Sierra Leone. Am J Trop Med Hyg 2007; 77:169.
  34. Keenlyside RA, McCormick JB, Webb PA, et al. Case-control study of Mastomys natalensis and humans in Lassa virus-infected households in Sierra Leone. Am J Trop Med Hyg 1983; 32:829.
  35. Ter Meulen J, Lukashevich I, Sidibe K, et al. Hunting of peridomestic rodents and consumption of their meat as possible risk factors for rodent-to-human transmission of Lassa virus in the Republic of Guinea. Am J Trop Med Hyg 1996; 55:661.
  36. Johnson KM, McCormick JB, Webb PA, et al. Clinical virology of Lassa fever in hospitalized patients. J Infect Dis 1987; 155:456.
  37. World Health Organization. Clinical Management of Patients with Viral Haemorrhagic Fever: A Pocket Guide for the front-line health worker, 30 March 2014. WHO, Geneva 2014 http://apps.who.int/iris/bitstream/10665/130883/2/WHO_HSE_PED_AIP_14.05.pdf?ua=1 (Accessed on April 21, 2016).
  38. Lunkenheimer K, Hufert FT, Schmitz H. Detection of Lassa virus RNA in specimens from patients with Lassa fever by using the polymerase chain reaction. J Clin Microbiol 1990; 28:2689.
  39. Centers for Disease Control and Prevention. What you need to know about Lassa Fever. https://www.cdc.gov/vhf/lassa/pdf/what-you-need-to-know-about-lassa-factsheet.pdf (Accessed on August 03, 2016).
  40. Stephenson EH, Larson EW, Dominik JW. Effect of environmental factors on aerosol-induced Lassa virus infection. J Med Virol 1984; 14:295.
  41. Monath TP, Mertens PE, Patton R, et al. A hospital epidemic of Lassa fever in Zorzor, Liberia, March-April 1972. Am J Trop Med Hyg 1973; 22:773.
  42. Fisher-Hoch SP, Tomori O, Nasidi A, et al. Review of cases of nosocomial Lassa fever in Nigeria: the high price of poor medical practice. BMJ 1995; 311:857.
  43. Bausch DG, Rollin PE, Demby AH, et al. Diagnosis and clinical virology of Lassa fever as evaluated by enzyme-linked immunosorbent assay, indirect fluorescent-antibody test, and virus isolation. J Clin Microbiol 2000; 38:2670.
  44. Jahrling PB, Hesse RA, Eddy GA, et al. Lassa virus infection of rhesus monkeys: pathogenesis and treatment with ribavirin. J Infect Dis 1980; 141:580.
  45. Callis RT, Jahrling PB, DePaoli A. Pathology of Lassa virus infection in the rhesus monkey. Am J Trop Med Hyg 1982; 31:1038.
  46. Walker DH, McCormick JB, Johnson KM, et al. Pathologic and virologic study of fatal Lassa fever in man. Am J Pathol 1982; 107:349.
  47. McCormick JB, Walker DH, King IJ, et al. Lassa virus hepatitis: a study of fatal Lassa fever in humans. Am J Trop Med Hyg 1986; 35:401.
  48. Peters CJ, Jahrling PB, Liu CT, et al. Experimental studies of arenaviral hemorrhagic fevers. Curr Top Microbiol Immunol 1987; 134:5.
  49. Roberts PJ, Cummins D, Bainton AL, et al. Plasma from patients with severe Lassa fever profoundly modulates f-met-leu-phe induced superoxide generation in neutrophils. Br J Haematol 1989; 73:152.
  50. Fennewald SM, Aronson JF, Zhang L, Herzog NK. Alterations in NF-kappaB and RBP-Jkappa by arenavirus infection of macrophages in vitro and in vivo. J Virol 2002; 76:1154.
  51. Edington GM, White HA. The pathology of Lassa fever. Trans R Soc Trop Med Hyg 1972; 66:381.
  52. Fisher-Hoch S, McCormick JB, Sasso D, Craven RB. Hematologic dysfunction in Lassa fever. J Med Virol 1988; 26:127.
  53. Demby AH, Chamberlain J, Brown DW, Clegg CS. Early diagnosis of Lassa fever by reverse transcription-PCR. J Clin Microbiol 1994; 32:2898.
  54. Trappier SG, Conaty AL, Farrar BB, et al. Evaluation of the polymerase chain reaction for diagnosis of Lassa virus infection. Am J Trop Med Hyg 1993; 49:214.
  55. Jahrling PB, Frame JD, Rhoderick JB, Monson MH. Endemic Lassa fever in Liberia. IV. Selection of optimally effective plasma for treatment by passive immunization. Trans R Soc Trop Med Hyg 1985; 79:380.
  56. Baize S, Marianneau P, Loth P, et al. Early and strong immune responses are associated with control of viral replication and recovery in lassa virus-infected cynomolgus monkeys. J Virol 2009; 83:5890.
  57. Mahanty S, Bausch DG, Thomas RL, et al. Low levels of interleukin-8 and interferon-inducible protein-10 in serum are associated with fatal infections in acute Lassa fever. J Infect Dis 2001; 183:1713.
  58. Lukashevich IS, Maryankova R, Vladyko AS, et al. Lassa and Mopeia virus replication in human monocytes/macrophages and in endothelial cells: different effects on IL-8 and TNF-alpha gene expression. J Med Virol 1999; 59:552.
  59. Mertens PE, Patton R, Baum JJ, Monath TP. Clinical presentation of Lassa fever cases during the hospital epidemic at Zorzor, Liberia, March-April 1972. Am J Trop Med Hyg 1973; 22:780.
  60. Monath TP, Maher M, Casals J, et al. Lassa fever in the Eastern Province of Sierra Leone, 1970-1972. II. Clinical observations and virological studies on selected hospital cases. Am J Trop Med Hyg 1974; 23:1140.
  61. Monson MH, Frame JD, Jahrling PB, Alexander K. Endemic Lassa fever in Liberia. I. Clinical and epidemiological aspects at Curran Lutheran Hospital, Zorzor, Liberia. Trans R Soc Trop Med Hyg 1984; 78:549.
  62. World Health Organization. Lassa fever. http://www.who.int/mediacentre/factsheets/fs179/en/ (Accessed on August 03, 2016).
  63. Cummins D, McCormick JB, Bennett D, et al. Acute sensorineural deafness in Lassa fever. JAMA 1990; 264:2093.
  64. Khan SH, Goba A, Chu M, et al. New opportunities for field research on the pathogenesis and treatment of Lassa fever. Antiviral Res 2008; 78:103.
  65. Okokhere PO, Ibekwe TS, Akpede GO. Sensorineural hearing loss in Lassa fever: two case reports. J Med Case Rep 2009; 3:36.
  66. Liao BS, Byl FM, Adour KK. Audiometric comparison of Lassa fever hearing loss and idiopathic sudden hearing loss: evidence for viral cause. Otolaryngol Head Neck Surg 1992; 106:226.
  67. McCormick JB. Clinical, epidemiologic, and therapeutic aspects of Lassa fever. Med Microbiol Immunol 1986; 175:153.
  68. Branco LM, Grove JN, Boisen ML, et al. Emerging trends in Lassa fever: redefining the role of immunoglobulin M and inflammation in diagnosing acute infection. Virol J 2011; 8:478.
  69. Solbrig MV. Headache syndromes in Sierra Leone, West Africa. Headache 1991; 31:419.
  70. Hirabayashi Y, Oka S, Goto H, et al. An imported case of Lassa fever with late appearance of polyserositis. J Infect Dis 1988; 158:872.
  71. Yanase O, Motomiya T, Watanabe K, et al. [Lassa fever associated with effusive constrictive pericarditis and bilateral atrioventricular annular constriction: a case report]. J Cardiol 1989; 19:1147.
  72. Cummins D, Bennett D, Fisher-Hoch SP, et al. Electrocardiographic abnormalities in patients with Lassa fever. J Trop Med Hyg 1989; 92:350.
  73. Cummins D, Fisher-Hoch SP, Walshe KJ, et al. A plasma inhibitor of platelet aggregation in patients with Lassa fever. Br J Haematol 1989; 72:543.
  74. Lange JV, Mitchell SW, McCormick JB, et al. Kinetic study of platelets and fibrinogen in Lassa virus-infected monkeys and early pathologic events in Mopeia virus-infected monkeys. Am J Trop Med Hyg 1985; 34:999.
  75. Price ME, Fisher-Hoch SP, Craven RB, McCormick JB. A prospective study of maternal and fetal outcome in acute Lassa fever infection during pregnancy. BMJ 1988; 297:584.
  76. Monson MH, Cole AK, Frame JD, et al. Pediatric Lassa fever: a review of 33 Liberian cases. Am J Trop Med Hyg 1987; 36:408.
  77. Schmitz H, Köhler B, Laue T, et al. Monitoring of clinical and laboratory data in two cases of imported Lassa fever. Microbes Infect 2002; 4:43.
  78. Frame JD. Clinical features of Lassa fever in Liberia. Rev Infect Dis 1989; 11 Suppl 4:S783.
  79. McCormick JB, King IJ, Webb PA, et al. Lassa fever. Effective therapy with ribavirin. N Engl J Med 1986; 314:20.
  80. Asogun DA, Adomeh DI, Ehimuan J, et al. Molecular diagnostics for lassa fever at Irrua specialist teaching hospital, Nigeria: lessons learnt from two years of laboratory operation. PLoS Negl Trop Dis 2012; 6:e1839.
  81. Günther S, Weisner B, Roth A, et al. Lassa fever encephalopathy: Lassa virus in cerebrospinal fluid but not in serum. J Infect Dis 2001; 184:345.
  82. Centers for Disease Control and Prevention. Lassa Fever: Diagnosis. https://www.cdc.gov/vhf/lassa/diagnosis/index.html (Accessed on August 02, 2016).
  83. Wulff H, Johnson KM. Immunoglobulin M and G responses measured by immunofluorescence in patients with Lassa or Marburg virus infections. Bull World Health Organ 1979; 57:631.
  84. Emmerich P, Günther S, Schmitz H. Strain-specific antibody response to Lassa virus in the local population of west Africa. J Clin Virol 2008; 42:40.
  85. Vieth S, Drosten C, Lenz O, et al. RT-PCR assay for detection of Lassa virus and related Old World arenaviruses targeting the L gene. Trans R Soc Trop Med Hyg 2007; 101:1253.
  86. Olschläger S, Lelke M, Emmerich P, et al. Improved detection of Lassa virus by reverse transcription-PCR targeting the 5' region of S RNA. J Clin Microbiol 2010; 48:2009.
  87. Boggild AK, Esposito DH, Kozarsky PE, et al. Differential diagnosis of illness in travelers arriving from Sierra Leone, Liberia, or Guinea: a cross-sectional study from the GeoSentinel Surveillance Network. Ann Intern Med 2015; 162:757.
  88. Haas WH, Breuer T, Pfaff G, et al. Imported Lassa fever in Germany: surveillance and management of contact persons. Clin Infect Dis 2003; 36:1254.
  89. Connor JD, Hintz M, Van Dyke R, et al. Ribavirin Pharmacokinetics in Children and Adults During Therapeutic Trials, Academic Press, Orlando, FL 1984.
  90. Lukashevich IS. Advanced vaccine candidates for Lassa fever. Viruses 2012; 4:2514.
  91. Centers for Disease Control and Prevention. Viral Hemorrhagic Fevers (VHFs): Information for Healthcare Workers. http://www.cdc.gov/vhf/abroad/healthcare-workers.html (Accessed on August 04, 2016).
  92. Bausch DG, Hadi CM, Khan SH, Lertora JJ. Review of the literature and proposed guidelines for the use of oral ribavirin as postexposure prophylaxis for Lassa fever. Clin Infect Dis 2010; 51:1435.
  93. Huggins JW. Prospects for treatment of viral hemorrhagic fevers with ribavirin, a broad-spectrum antiviral drug. Rev Infect Dis 1989; 11 Suppl 4:S750.
  94. Bossi P, Tegnell A, Baka A, et al. Bichat guidelines for the clinical management of haemorrhagic fever viruses and bioterrorism-related haemorrhagic fever viruses. Euro Surveill 2004; 9:E11.
  95. Crowcroft NS. Management of Lassa fever in European countries. Euro Surveill 2002; 7:50.
  96. Holmes GP, McCormick JB, Trock SC, et al. Lassa fever in the United States. Investigation of a case and new guidelines for management. N Engl J Med 1990; 323:1120.