|Tasmania devil Sarcophilus harrisii|
A little over 30 years ago, Tasmanian devils, marsupials that lives only on the Australian island of Tasmania, began to develop fatal tumours on their face. It was subsequently found that this devil facial tumour disease (DFTD) was a transmissible cancer which is passed on when one animal bites another on the face and transfers live tumour cells to the new host.
It is thought that these transmitted cells are not recognised by the devils' immune system as foreign and so destroyed because they are genetically so close to the devil's own cells having developed in a highly in-bred population as the population declined and genetic diversity declined with it. Ironically, a parasite has arisen in a host, derived from the host itself.