Key facts Lassa fever is an acute viral illness caused by the Lassa virus The disease is spread to humans primarily through contact with infected rodents or items contaminated with their urine and faeces Person-to-person transmission can occur, especially in hospitals or clinics where there is poor infection control Most people infected with Lassa virus experience mild symptoms, but the disease can be severe or fatal Lassa fever is endemic in parts of west Africa Overview Lassa fever is an acute viral haemorrhagic illness that comes on quickly after infection. The Lassa virus, which causes the fever, belongs to the Arenaviridae virus family. The disease was first identified in 1969 in Nigeria, but has also been found in Benin, Ghana, Guinea, Liberia, Mali and Sierra Leone. Lassa fever is a zoonotic disease, meaning that it spreads from animals to humans. The main animal reservoir for the virus is the multimammate rat ( Mastomys natalensis ), which is common throughout sub-Saharan Africa.…