Bats or rodents, who started it? Short history of the gibbon ape leukaemia virus–koala retrovirus clade. In Proceedings of the Second Koala Retrovirus Workshop, ed. D. E. Alquezar-Planas, D. P. Higgins, C. L. Singleton, and A. D. Greenwood

The close genetic relationship between gibbon ape leukaemia virus (GALV) and koala retrovirus (KoRV) has puzzled scientists since its discovery. As the two hosts are separated geographically and taxonomically, it was hypothesized that cross-species transmission of an ancestor virus from another host into gibbons and koalas had occurred. The relatively recent introduction of KoRV into the koala genome and the apparent absence of GALV in wild gibbons suggest that this ancestor virus or a close relative may still be in circulation. Investigation into the nature of this ancestor virus may provide insights on the impact of KoRV on declining koala populations and will also broaden our understanding of host-virus coevolution. A variety of mammalian species have been identified to harbor GALV-like viruses, but the true host of the ancestral virus of KoRV and GALV remains uncertain. Here we provide a short history of the most prominent candidates: rodents and bats.