Lassa fever

Last reviewed: 6 Jan 2023
Last updated: 28 Oct 2022



History and exam

Key diagnostic factors

  • presence of risk factors
  • fever ≥37.5°C
  • elevated respiratory rate
  • low systolic blood pressure
  • malaise
  • nausea/vomiting
  • headache
  • sore throat/pharyngitis
  • conjunctivitis
  • chest pain/cough
  • myalgia
  • deafness (sensorineural)
  • facial oedema
  • bleeding
More key diagnostic factors

Other diagnostic factors

  • abdominal pain
  • diarrhoea
  • confusion and altered Glasgow Coma Scale or seizures
  • effusions
Other diagnostic factors

Risk factors

  • occupational exposure
  • living/working in, or arrival from, endemic area
  • contact with infected body fluids
  • butchering and/or eating rodent meat
  • bioterrorism
More risk factors

Diagnostic investigations

1st investigations to order

  • reverse transcription-polymerase chain reaction (RT-PCR)
  • serology
  • rapid diagnostic lateral flow assay
  • rapid diagnostic test for malaria
  • blood culture for typhoid
More 1st investigations to order

Investigations to consider

  • renal function
  • serum electrolytes
  • blood lactate/ABG
  • FBC
  • coagulation studies
  • liver function tests
  • chest x-ray
  • urinalysis
  • blood cultures
  • lumbar puncture
  • abdominal ultrasound
More investigations to consider

Treatment algorithm


potential exposure


suspected infection or symptomatic



Catherine Houlihan, MBChB, PhD

Clinical Lecturer in Infectious Diseases/Virology

University College London




CH declares that she has no competing interests.


Dr Catherine Houlihan would like to gratefully acknowledge Dr Ron Behrens, a previous contributor to this topic.


RB has provided expert testimony to the courts, on behalf of the Crown, regarding Q fever. RB has been a paid member of the Advisory Board for Takeda regarding Dengue vaccine. He has been a paid member of the Advisory Board for Valneva UK regarding Ixiaro, a vaccine for Japanese encephalitis.

Peer reviewers

John S. Schieffelin, MD, MSPH

Assistant Professor of Medicine & Pediatrics

Tulane University School of Medicine

New Orleans



JSS is a paid reviewer and author of articles on UpToDate.

Michael Brown, BA, BM, BCh, FRCP, PhD, DTM&H

Consultant Physician

Hospital for Tropical Diseases

University College London Hospitals




MB is Clinical Lead of the Hospital for Tropical Diseases, a contributing partner to the PHE Imported fever service that co-ordinates testing of samples from UK patients for viral haemorrhagic fevers.

Stephen Gluckman, MD

Professor of Medicine

Perelman School of Medicine at the University of Pennsylvania




SG declares that he has no competing interests.

  • Differentials

    • Malaria infection
    • Typhoid infection
    • Ebola virus infection
    More Differentials
  • Guidelines

    • Lassa fever: origins, reservoirs, transmission and guidelines
    • CDC Yellow Book 2020: health information for international travel - Viral hemorrhagic fevers
    More Guidelines
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