Abstract Marburg and Ebola viruses cause severe and often fatal haemorrhagic disease in humans and non-human primates. They are the two established members of the family Filoviridae and have a distinctive filamentous and irregular morphology with a genome consisting of a very large (about 19 kb) single-stranded RNA of negative polarity. Features of their organization and structure at the molecular level have led to their inclusion in the taxonomic order Mononegavirales, together with the paramyxoviruses and the rhabdoviruses.