Viral hemorrhagic fevers (VHFs) are a diverse group of animal and human illnesses in which fever and hemorrhage are caused by a viral infection. VHFs may be caused by five distinct families of RNA viruses: the families Filoviridae, Flaviviridae, Rhabdoviridae, and several member families of the Bunyavirales order such as Arenaviridae, and Hantaviridae. All types of VHF are characterized by fever and bleeding disorders and all can progress to high fever, shock and death in many cases. Some of the VHF agents cause relatively mild illnesses, such as the Scandinavian nephropathia epidemica (a hantavirus), while others, such as Ebola virus, can cause severe, life-threatening disease. Signs and symptoms Signs and symptoms of VHFs include (by definition) fever and bleeding: Flushing of the face and chest, small red or purple spots (petechiae), bleeding, swelling caused by edema, low blood pressure (hypotension), and circulatory shock. Malaise, muscle pain, headache, vomiting, and diarrhea occur frequently. The severity of symptoms varies with the type of virus. The "VHF syndrome" (capillary leak, bleeding diathesis, and circulatory compromise leading to shock) appears in a majority of people with filoviral hemorrhagic fevers (e.g., Ebola and Marburg virus), Crimean–Congo hemorrhagic fever (CCHF), and the South American hemorrhagic fevers caused by arenaviruses, but only in a small minority of patients with dengue or Rift Valley fever. Causes Five families of RNA viruses have been recognised as being able to cause hemorrhagic fevers. The order Bunyavirales includes the families Arenaviridae, Fimoviridae, and all members of the former family Bunyaviridae, especially Peribunyaviridae. The family Arenaviridae include the viruses responsible for Lassa fever (Lassa virus), Lujo virus, Argentine (Junin virus), Bolivian (Machupo virus), Brazilian (Sabiá virus), Chapare hemorrhagic fever (Chapare virus), Venezuelan (Guanarito virus) and Whitewater Arroyo virus hemorrhagic fevers. The former family Bunyaviridae includes the causative agents of Hantavirus hemorrhagic fever with renal syndrome (HV-HFRS) (Hantaviridae), the Crimean-Congo hemorrhagic fever (CCHF) virus from the genus Orthonairovirus (Nairoviridae), Garissa virus and Ilesha virus from the genus Orthobunyavirus (Peribunyaviridae), and the Rift Valley fever (RVF) virus from the genus Phlebovirus (Phenuiviridae). The family Filoviridae (order Mononegavirales) includes Ebola virus and Marburg virus. The family Flaviviridae (order Amarillovirales) includes dengue, yellow fever, and two viruses in the tick-borne encephalitis group that cause VHF: Omsk hemorrhagic fever virus and Kyasanur Forest disease virus. The family Togaviridae (order Martellivirales) includes Chikungunya virus which causes Chikungunya fever. Family Rhabdoviridae (order Mononegavirales): In September 2012 scientists writing in