Lassa fever is a viral haemorrhagic illness that was first discovered in 1969 when two missionary nurses died from the illness in the Nigerian town of Lassa. The Lassa virus is a zoonotic or animal-borne virus and the animal vector is the “multimammate rat” (Mastomys natalensis). The virus is a single-stranded RNA virus and is a member of the arena virus family. Lassa fever occurs naturally in the West African countries of Sierra Leone, Liberia, Guinea and Nigeria. Sporadic cases have also been reported from Central African Republic, Burkina Faso, Côte d’Ivoire, Mali, Togo, Benin, Senegal, Ghana and Democratic Republic of Congo.