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Clinical Review

Lassa fever: epidemiology, clinical features, and social consequences

BMJ 2003; 327 doi: (Published 27 November 2003) Cite this as: BMJ 2003;327:1271

This article has corrections. Please see:

  1. J Kay Richmond, freelance consultant (,
  2. Deborah J Baglole, health adviser2
  1. 124 Llantrisant Rise, Llandaff, Cardiff CF5 2PG
  2. 2Merlin, Borough, London SE1 1DB
  1. Correspondence to: J K Richmond


    Lassa fever is a viral haemorrhagic fever transmitted by rats. It has been known since the 1950s, but the virus was not identified until 1969, when two missionary nurses died from it in the town of Lassa in Nigeria. Found predominantly in west Africa,1 it has the potential to cause tens of thousands of deaths. Even after recovery, the virus remains in body fluids, including semen.1 The years of civil unrest in Sierra Leone (1991-2002) halted the investigation (through international collaboration) of Lassa fever at a specialist unit in Kenema. Increasing international travel and the possibility of use of the Lassa virus as a biological weapon escalate the potential for harm beyond the local level. Access to the country is improving, so renewed efforts to understand it are feasible.

    Method of review

    The information presented comes from a strategic document produced in 2002 for Merlin (Medical Emergency Relief International, a London based nongovernmental aid organisation which manages the Lassa unit in Kenema ( This document, ‘Licking’ Lassa fever,2 was created through collaboration with experts in infectious disease, community development, clinical management of viral haemorrhagic diseases, and qualitative research. The sources of information were a literature review using Ovid and PubMed (search term “Lassa fever”), case analysis and surveys undertaken in the field, and relevant websites (such as those of the World Health Organization, Centers for Disease Control and Prevention).


    Lassa fever is caused by a single stranded RNA virus and is a disseminated systemic primary viral infection.3 4 The main feature of fatal illness is impaired or delayed cellular immunity leading to fulminant viraemia.5 The prevalence of antibodies to the virus in the population is 8-52% in Sierra Leone,6 4-55% in Guinea,7 and 21% in Nigeria.8 Seropositivity has also been found in the Central …

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