Lassa fever epidemiology and demographics
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Epidemiology and Demographics
Lassa virus is zoonotic (transmitted from animals), and that it spreads to man from rodents, specifically multi-mammate rats (Mastomys natalensis). This is probably the most common rodent in equatorial Africa, ubiquitous in human households and eaten as a delicacy in some areas. In these rats infection is in a persistent asymptomatic state. The virus is shed in their excreta (urine and feces), which can be aerosolized. In fatal cases, Lassa fever is characterized by impaired or delayed cellular immunity leading to fulminant viremia.
The dissemination of the infection can be assessed by prevalence of antibodies to the virus in populations of:
- Sierra Leone 8–52%
- Guinea 4–55%
- Nigeria approx. 21%
Like other hemorrhagic fevers, Lassa fever can be transmitted directly from one human to another. It can be contracted by an airborne route or with direct contact with infected human blood, urine, or semen. Transmission through breast milk has also been observed.
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%. Also the mortality rate is higher, greater than 80%, when it occurs in pregnant women during their third trimester; fetal death also occurs in nearly all those cases. Abortion decreases the risk of death to the mother.