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Lassa fever (lăsˈə), an acute viral disease occurring mostly in W Africa, characterized by high fever, muscle aches, mouth ulcers, and bleeding in the skin in more severe cases. The disease was first recognized in Lassa, Nigeria, in 1969. The causative virus is an arenavirus and is harbored by a rat, Mastomys natalensis. The virus is spread to humans via the rat's urine in airborne droplets or contaminated food. The disease can also be caught by medical personnel treating patients in hospitals.
The incubation period of Lassa fever is 3 to 17 days. In some 80% of the cases the symptoms are mild and typically undiagnosed. In more serious cases, following fever and general malaise, later stages of the disease may include abdominal pain, diarrhea, vomiting, and petechiae, tiny purplish spots in the skin caused by leakage of blood from the capillaries. Heart and kidney failure may also occur in severe cases. Although only an estimated 1% die from the disease, mortality is high among those hospitalized with Lassa fever, ranging from about 15% to, among pregnant women, as much as 60%. In epidemics, however, about half of all hospitalized patients may die, and spontaneous abortion occurs in 95% of infected pregnant women. Treatment by injection of the antiviral drug ribavirin is often successful if begun early.
See also hemorrhagic fever.