Lassa Fever

About Lassa Fever

Lassa fever is a viral hemorrhagic fever caused by the Lassa arenavirus, first identified in 1969 in Lassa, Nigeria. The virus is transmitted to humans through contact with food or household items contaminated by urine or feces of the multimammate rat Mastomys natalensis. An estimated 100,000 to 300,000 Lassa fever infections occur annually in West Africa, with approximately 5,000 deaths. The case fatality rate is approximately 1 percent overall but can reach 15 percent or more among hospitalized patients. Pregnant women have particularly severe outcomes, with maternal death or fetal loss reported in a large majority of cases in late pregnancy. The antiviral ribavirin has been used in treatment, though the evidence for its effectiveness is debated. Lassa fever is endemic in Nigeria, Sierra Leone, Guinea, and Liberia. Several Lassa vaccine candidates, including one developed by IAVI, have entered clinical trials. Lassa fever is on the WHO list of priority diseases for research and development.