Lassa fever is an acute viral illness, transmitted to humans by rodents. It occurs in West Africa. Primary transmission can be prevented by avoiding contact with rodents and their excrements, especially in regions in which outbreaks occur.
While about 80% of the infections go with no symptoms, the remaining patients develop severe multi-system disease and up to 15% of the hospitalized cases may die. Early treatment with the antiviral drug ribavirin is effective, and infection is prevented through good hygiene conditions.