Lassa Fever

Aka: Lassa Fever, Lassa Virus

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II. Epidemiology

  1. First recognized Outbreak: Lassa, Nigeria (1969)
  2. Endemic to West Africa
    1. Nigeria
    2. Liberia
    3. Sierra Leone
    4. Senegal
    5. Gambia
    6. Guinea
    7. Ghana
    8. Burkina Faso (Upper Volta)
    9. Mali
    10. Ivory Coast

III. Pathophysiology

  1. Lassa Virus is an Arenavirus that is classified as a Viral Hemorrhagic Fever
  2. Arenaviruses (Arenaviridae) are a family of viruses causing Viral Hemorrhagic Fever
    1. Arenaviridae primarily cause Viral Hemorrhagic Fever (except LCMV)
    2. Arenaviridae are Enveloped, helical, segmented, single stranded RNA Viruses
    3. Arenaviridae infect rodents as main reservoir, and transmit to humans via contact with urine
  3. Arenaviruses are Anti-Message Sense RNA Viruses (Negative Stranded, -ssRNA)
    1. Anti-Message sense RNA (-ssRNA) need to first be transcribed into +ssRNA
    2. RNA dependent RNA Polymerase (RNA replicase, RdRp)
      1. RdRp is an enzyme carried by the -ssRNA virus within its capsid
      2. RdRp transcribes -ssRNA into +ssRNA within the host cell
    3. Translation follows +ssRNA transcription from -ssRNA (by RdRp)
      1. As with mRNA, +ssRNA translated by host ribosomes into Protein
  4. Transmission
    1. Incubation: 1-24 days
    2. Multimammate Rats (Mastomys natalensis) are reservoir
      1. Contamination of food with rodent urine
    3. Person to person blood or body fluid contact
      1. Urine
      2. Feces
      3. Vomit
      4. Saliva

IV. Symptoms

  1. Early, Insidious symptoms
    1. Fever (100%)
    2. Chills
    3. Rigors
    4. Headache (50%)
    5. Malaise (100%)
    6. Myalgia (50%)
  2. Second week symptoms
    1. Lower Abdominal Pain
    2. Intractable Vomiting
  3. Other symptoms
    1. Tinnitus
    2. Epistaxis
    3. Bleeding Gums
    4. Maculopapular rash
    5. Cough
    6. Dizziness

V. Signs

  1. Early
    1. Fever
    2. Flushing of face and V-neck area
    3. Pharyngitis (progressive over first week)
      1. Raised patch of whitish exudate on Tonsillar Pillar
      2. Pseudomembranes may develop
      3. Oral Ulcerations (50%)
    4. Generalized non-tender Lymphadenopathy (50%)
  2. Later
    1. Facial and neck swelling
    2. Conjunctivitis
  3. Severe, Acute Phase
    1. Systolic Blood Pressure below 90 (60-80%)
    2. Pulse Pressure less than 20
    3. Relative Bradycardia

VI. Labs

  1. Complete Blood Count
    1. Hematocrit normal
    2. White Blood Cell Count low (Leukopenia)
      1. Relative Neutrophilia
  2. Erythrocyte Sedimentation Rate normal
  3. Liver Function Tests
    1. Aspartate Aminotransferase (AST, SGOT) elevated
    2. Creatinine phosphokinase (CPK) elevated
    3. Lactate Dehydrogenase (LDH) elevated
  4. Urinalysis
    1. Severe Proteinuria
  5. Lassa Virus Antibody titer
    1. Fourfold rise between acute and convalescent phase

VII. Radiology

  1. Chest XRay
    1. Basilar pneumonitis
    2. Pleural Effusions

VIII. Diagnostics

  1. Electrocardiogram
    1. May show diffuse Myocardial Disease

IX. Complications

  1. Oculogyric Crisis (rapid involuntary eye movement)
  2. Deafness
  3. Alopecia

X. Course

  1. Illness lasts 7 to 31 days (average 12-15 days)

XI. Prognosis

  1. Mortality: 8 to 52%
  2. Signs suggestive of poor prognosis or death
    1. Shock
    2. Altered Level of Consciousness
    3. Auscultated Rales
    4. Pleural Effusion
    5. Grand Mal Seizures

XII. Differential Diagnosis

  1. Hemorrhagic FeverViruses

XIII. Management

  1. Supportive care
  2. Ribavirin (Virazole)
    1. See Viral Hemorrhagic Fever for protocol
    2. Appears highly effective
  3. Infusion of immune plasma from convalescent patients
  4. Isolation Procedures
    1. Respiratory isolation
    2. Blood and Body fluid precautions

XIV. References

  1. Seeyave (2015) Crit Dec Emerg Med 29(5): 13-21
  2. Wilson (1991) Harrison's PIM, Mcgraw Hill, pp. 740-1

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