Genome-invading retroviruses are a nasty surprise

An international team of scientists, including Dr Simon Ho from the University of Sydney, has found that the koala genome is slowly being invaded by a retrovirus associated with Chlamydia infection and leukaemia.

Unlike other viruses, retroviruses must actually copy their genetic material into the host genome as part of their life cycle. On occasion, a retrovirus integrates into the reproductive cells of the host, thus becoming a permanent part of the host’s genome. Koalas are the only known case where this process can be seen in action. Dr Ho and colleagues have found this process can take much longer than expected – the virus can continue to have a serious pathological impact on the host for centuries.

The team discovered a number of surprises when they examined koala museum skins from the late 19th and 20th centuries. They found that the retrovirus was already widespread 120 years ago in koalas in northern Australia, and that the virus genome has shown little change over the course of a century. This suggests that ancient forms of the virus would have caused similar pathologies.

Alex Greenwood of the Leibniz Institute for Zoo and Wildlife Research in Berlin, leader of the research consortium, notes that “this actually makes sense as koalas are quite sedentary, so it is hard to imagine how koala retrovirus would have spread through the entire population in the short time of 200 years. The koala retrovirus might be more than a thousand or even ten thousand years old, unfortunately we have no older specimens.”

Read the scientific publication here:
One hundred twenty years of koala retrovirus evolution determined from museum skins
Ávila-Arcos, Ho, Ishida, Nikolaidis, Tsangaras, et al. (2012) Molecular Biology and Evolution, 30: 299–304