Jeff J. McKee, Lindell D. Bromham, Nidia M. Oliveira and Maribeth V. Eiden

Endogenous retroviruses (ERVs) are present in the genomes of most eukaryotic taxa.  After entering the genome of a species ERVs are transmitted vertically as normal genetic constituents.  Once integrated, most ERVs become genetically inert but some retain the ability to produce horizontally infective (exogenous) virus. Given their simple inheritance pattern ERVs should “host track” over evolutionary time; that is, taxonomically related hosts should carry ERVs that are proportionately related.  In addition ecologically related hosts that come into close contact may share related ERVs if those ERVs have retained infectivity. One of the most obvious exceptions to ‘host tracking’ is seen when comparing Koala Retrovirus (KoRV) and Gibbon Ape Leukaemia Virus (GALV).  KoRV and GALV share such a close sequence similarity across all loci that it likely that they have only recently diverged. However their respective hosts, koalas Phascolarctos cinereus and gibbons Hylobates spp., are taxonomically remote and have no defined ecological overlap – implying that simple viral transmission between them is improbable. There is evidence to support possible indirect viral transmission between gibbons and koalas either via endemic rodents, pteropid bats or iatrogenic transfer but to date none of these hypotheses adequately explain the unique similarity and infection profiles of GALV and KoRV. We are attempting to resolve a more precise viral transmission path using in vitro host range assays and by bioinformatic analysis of ERV DNA sequence data from a range of related hosts.  At a broader level, this type of approach may provide useful information to conservation managers on species mixing, pathogen transfer and gene flow within a system.