Ravn virus  Ravn virus (; RAVV) is a close relative of the much more commonly known Marburg virus (MARV). RAVV causes Marburg virus disease in humans and nonhuman primates, a form of viral hemorrhagic fever. RAVV is a Select agent, World Health Organization Risk Group 4 Pathogen (requiring Biosafety Level 4-equivalent containment), National Institutes of Health/National Institute of Allergy and Infectious Diseases Category A Priority Pathogen, Centers for Disease Control and Prevention Category A Bioterrorism Agent, and listed as a Biological Agent for Export Control by the Australia Group. Ravn virus (today abbreviated RAVV, but then considered identical to Marburg virus) was first described in 1987 and is named after a 15-year old Danish boy that got sick and died by it. Today, the virus is classified as one of two members of the species "Marburg marburgvirus", which is included into the genus "Marburgvirus", family "Filoviridae", order "Mononegavirales". The name Ravn virus is derived from "Ravn" (the name of the Danish patient from whom this virus was first isolated) and the taxonomic suffix "virus". According to the rules for taxon naming established by the International Committee on Taxonomy of Viruses (ICTV), the name Ravn virus is always to be capitalized, but is never italicized, and may be abbreviated (with RAVV being the official abbreviation). Ravn virus was first introduced as a new "subtype" of Marburg virus in 1996. In 2006, a thorough whole-genome analysis of all marburgviruses revealed the existence of five distinct genetic lineages. The genomes of representative isolates of four of those lineages differed from each other by only 0-7.8% on the nucleotide level, whereas representatives of the fifth lineage, including the new "subtype", differed from those of the other lineages by up to 21.3%. Consequently, the fifth genetic lineage was reclassified as a virus, Ravn virus (RAVV), distinct from the virus represented by the four more closely related lineages, Marburg virus (MARV). A virus that fulfills the criteria for being a member of the species "Marburg marburgvirus" is a Ravn virus if it has the properties of Marburg marburgviruses and if its genome diverges from that of the prototype Marburg marburgvirus, Marburg virus variant Musoke (MARV/Mus), by ≥10% but from that of the prototype Ravn virus (variant Ravn) by <10% at the nucleotide level.