Current drug treatment of Lassa fever and certain New World hemorrhagic fevers is limited to the guanosine analogue ribavirin [7, 8, 9] . Although ribavirin therapy can reduce the mortality rates of severe clinical cases, its unavailability to most patients in West Africa and South America as well as its association with severe adverse effects including anaemia [11, 13] , teratogenicity and embryo lethality [12] , argues for the development of new alternative treatment options.