Lassa virus

Background

Microbiology

• Negative-sense, single-stranded RNA virus within the Arenaviridae family
• Genome in small (S) and large (L) segments
• Covered in glycoprotein spikes, and cell ribosomes are visible inside

Epidemiology

• West Africa, particulary in Guinea, Sierra Leone, Liberia, Mali, Côte d'Ivoire, Ghana, Togo, Benin, Burkina Faso, and Nigeria
  • Endemic in Guinea, Sierra Leone, Liberia, and Nigeria
  • In Sierra Leone and Liberia, up to 10-15% of hospital admission are due to Lassa fever
• Reservoir is Mastomys species multimammate mouse, as well as African wood mouse
• Associated with bush meat hunting
• 59 million people at risk with up to 3 million cases annually causing 67,000 deaths
• More common in dry season when the rats are more likely to search to food within human habitats

Clinical Manifestations

• Incubation period up to 21 days
• Wide range of severity
  • Likely 30 asymptomatic or very mild cases for every symptomatic case
  • Mild symptoms in 80% of cases
• Hearing loss in 30%, which can be permanent
• Unlike other viral hemorrhagic fevers, subcutaneous bleeding and rash is uncommon
• Facial edema has been described
• Seizures in encephalopathy
• Mortality about 1%, but up to 65% in hospitalized patients

Diagnosis

• National Microbiology Lab can do PCR, virus isolation, and serology
  • Peak viremia 4 to 9 days after symptom onset, so may need to retest
• Rapid antigen test Corgenix ReLASV, not licensed in Canada
• Co-endemic with malaria and typhoid so test for those as well

Management

• Supportive care with IV fluids and electrolytes as necessary
• Avoid NSAIDs due to bleeding risk
• Ribavirin may be helpful especially early in disease, per WHO
• Experimental medications include favipiravir

Prevention

Infection Prevention and Control

• Isolate patient
• Droplet and contact precautions, with gloves, gown, and eye protection