Transmission electron micrograph (TEM) of the Marburg virus. Marburg virus (MARV) is a hemorrhagic fever virus of the Filoviridae family of viruses and a member of the species Marburg marburgvirus, genus Marburgvirus. MARV causes Marburg virus disease in humans and nonhuman primates, a form of viral hemorrhagic fever. The virus is considered to be extremely dangerous. The WHO rates it as a Risk Group 4 Pathogen (requiring biosafety level 4-equivalent containment). In the United States, the NIH/NIAID ranks it as a Category A Priority Pathogen and the CDC lists it as a Category A Bioterrorism Agent. It is also listed as a biological agent for export control by the Australia Group. Magnification unknown.