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Lassa fever is a viral haemorrhagic fever caused by an arenavirus, excreted in the urine of rats in West Africa. Contaminated dust and food, as well as person-to-person spread results in the development of the disease after an incubation period of one to three weeks.
The disease has an insidious onset, starting with a sore throat. Other features include:
The virus can be isolated from the urine, blood or throat washings of an infected person.
Treatment with ribavirin in the first week of disease reduces mortality by half. Serum from convalescent patients, which contain a high level of neutralising antibody, as used in treating Argentine haemorrhagic fever is controversial.
Mortality in epidemics may approach 50% but subclinical infection is common in endemic areas.