It is possible to trace the history of virus infections in vertebrate DNA. Since millions of years ago, these genomes have been storing the code of retroviruses that got into germline cells and were passed down as endogenous retroviruses (ERVs). Researchers from Uppsala University have discovered new information regarding the establishment of retroviruses in the koala genome. The findings were reported in the PNAS journal.

When the scientists looked at the koala genome, they found new ERV lineages in addition to the koala retroviruses (KoRV) they already knew about. KoRV has been linked to diseases in koalas, like cancer, and is on its way to becoming an ERV in the population. This has led to the koala being viewed as a possible model for the rapid spread of retroviruses and associated health consequences, a potential that has now been bolstered by the unexpected distribution pattern of novel ERV lineages.

““By screening available koala genomes, we have identified novel ERV lineages. One of these is related to the squirrel monkey retrovirus, which is normally found in South/Central America. Many ERVs of this type are only found in a few koala individuals ,” says Mette Lillie, the study’s principal author, “which indicates that they are relatively new. It may even indicate an ongoing establishment in the population.”

Researchers can draw comparisons between novel ERVs and retroviruses that are already establishing themselves, such as KoRV, thanks to large-scale sequencing of complete genomes from species populations. Based on how ERVs are spread out in the population and how different ERV lineages are, the researchers think that there may be more active retroviruses in koalas and other animals that live in the same environment. The findings are fueling the hunt for possibly active retroviruses in the Australian fauna that have yet to be discovered.

“The ERVs that have been left behind after retrovirus infections in the past now make it possible to uncover historical interactions between retroviruses and animal species, such as mapping how virus transmission has taken place,” adds the study lead Patric Jern. “Variations in ERV distribution patterns within host populations can also be valuable as genomic markers, for example in management and protection of endangered species.”

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