Lassa virus

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Lassa virus


Human and animal

Transmission/Exposure Routes

The virus can be transmitted through direct contact with these materials, through touching objects or eating food contaminated with these materials, or through cuts or sores. Contact with the virus also may occur when a person inhales tiny particles in the air contaminated with rodent excretions. Infection may occur via direct contact when they are caught and prepared for food. Person-to-person transmission is common.[1]

Case Fatality Ratios

Case-fatality rates of patients with VHF vary from less than 10% (eg, in dengue HF) to approximately 90%, as has been reported in patients with Ebola-Zaire and the recent Angola Marburg outbreak. The most recent outbreak of Ebola-Sudan in Uganda had a 50% case-fatality rate.[2]
About 15%-20% of hospitalized Lassa fever patients will die from the illness. It is estimated that the overall mortality rate is 1%, however during epidemics mortality can climb as high as 50%. The mortality rate is greater than 80% when it occurs in pregnant women during their third trimester; fetal death also occurs in nearly all those cases.[3]

Incubation Times

1-3 weeks [1]

Burden of Disease

The number of Lassa virus infections per year in West Africa is estimated at 100,000 to 300,000, with approximately 5,000 deaths. [1]
In some areas of Sierra Leone and Liberia, it is known that 10%-16% of people admitted to hospitals have Lassa fever. [1]

Duration of infectiousness and disease



Asymptomatic Rates

Excretion Rates (see Exposure)



A member of the virus family Arenaviridae, is a single-stranded RNA virus and is zoonotic, or animal-borne [1]

Environmental Survival

Recommended Dose Response Model

Dose response models for Lassa virus
Exponential, k is 2.95
Exponential model.png


  1. 1.0 1.1 1.2 1.3 1.4
  2. emachine.medscape
  3. Wikipedia