study done in 1995 and 1996 found that the genes of ebolavirus and marburgvirus differed by about 55% at the nucleotide level, and at least 67% at the amino acid level. the same study found that the strains of ebolavirus differed by about 37–41% across the nucleotide level and 34–43% across the amino acid level. the ebov strain was found to have an almost 2% change in the nucleotide level from the original 1976 strain from the yambuki outbreak and the strain from the 1995 kikwit outbreak. however, paleoviruses of filoviruses found in mammals indicate that the family itself is at least tens of millions of years old. genus organization and common names the genus ebolavirus has been organized into six species; however, the nomenclature has proven somewhat controversial, with many authors continuing to use common names rather than species names when referring to these viruses. in particular, the generic term "ebola virus" is widely used to refer specifically to members of the species zaire ebolavirus. consequently, in 2010, a group of researchers recommended that the name "ebola virus" be adopted for a subclassification within the species zaire ebolavirus and that similar common names be formally adopted for other ebolavirus species. in 2011, the international committee on taxonomy of viruses (ictv) rejected a proposal (2010.010bv) to formally recognize these names, as they do not designate names for subtypes, variants, strains, or other subspecies level groupings. as such, the widely used common names are not formally recognized as part of the taxonomic nomenclature. in particular, "ebola virus" does not have an official meaning recognized by ictv, and rather they continue to use and recommend only the species designation zaire ebolavirus. the threshold for putting isolates into different species is usually a difference of more than 30% at the nucleotide level, compared to the type strain. if a virus is in a given species but differs from the type strain by more than 10% at the nucleotide level, it is proposed that it be named as a new virus. as of 2019, none of the ebolavirus species contain members divergent enough to receive more than one "virus" designation. genus ebolavirus: species and viruses species name (abbreviation) virus common name (abbreviation) bombali ebolavirusbombali virus (bomv) bundibugyo ebolavirus (bebov) bundibugyo virus (bdbv) reston ebolavirus (rebov) reston virus (restv) sudan ebolavirus (sebov) sudan virus (sudv) taï forest ebolavirus (tebov; previously ciebov) taï forest virus (tafv) zaire ebolavirus (zebov) ebola virus (ebov) research a 2013 study isolated antibodies from fruit bats in bangladesh, against ebola zaire and reston viruses, thus identifying potential virus hosts and signs of the filoviruses in asia. a recent alignment-free analysis of ebola virus genomes from the current outbreak reveals the presence of three short dna sequences that appear nowhere in the human genome, suggesting that the identification of specific species sequences may prove to be useful for the development of both diagnosis and therapeutics. notes the kuhn et al. 2010 proposal specifically suggested that "ebola virus" be given a taxonomic rank of "virus" within the species zaire ebolavirus. in their proposal, an "ebola virus" would be any member of species zaire ebolavirus whose genome diverged from the type variant zaire ebolavirus (mayinga) by less than 10%. in general, the members of species zaire ebolavirus are allowed to genetically diverge from the mayinga type variant by up to 30%. as a result, this proposal would make "ebola virus" a subset of the species zaire ebolavirus rather than a common name synonym. the distinction of treating "ebola virus" as a subset of the species rather than as a synonym for the species is rarely used.