Lassa virus is an Old World Mammarenavirus that causes a viral hemorrhagic fever disease and is classified as biosafety-level 4 pathogen. It occurs in several countries in West Africa like Guinea, Sierra Leone, Liberia and Nigeria. Due to the lack in medical infrastructure in some of the regions where the virus occurs, no clear epidemiological data are available. However scientists estimate up to 300,000 infections occurring annually. Recent estimates report a case fatality rate of 30% in hospitalised patients. The virus is transmitted via rodents but also from human-to-human. Seroprevalence studies suggest that many people come in contact with the virus but only some fall seriously ill.