Lassa fever (lăsˈə) [key], a severe viral disease occurring mostly in W Africa, characterized by high fever, muscle aches, mouth ulcers, and bleeding in the skin. The disease was first recognized in Lassa, Nigeria, in 1969. The causative virus belongs to a group called arenaviruses 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. 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, and mortality is high, ranging from about 15% to, among pregnant women, as much as 60%. Treatment by injection of the antiviral drug ribavirin is often successful if begun early.
See also hemorrhagic fever.