Koalas are facing multiple environmental and health issues which threaten their survival. Along with habitat loss – accelerated by last year’s devastating bush fires – domestic dog attacks and road accidents, they suffer from deadly chlamydial infections and extremely high frequency of cancer. An international team of scientists led by the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW) now demonstrate that a retrovirus invading the koala germline explains the high frequency of koala cancer. The results are reported in the journal Nature Communications.