Tamsin Jones, Laboratory for Evolution and Development
Last week a Tasmanian devil named Cedric passed away. He was 6 years old, which is the average lifespan of a Tasmanian devil; however, his death was reported internationally.
Why? His cause of death was the devil facial tumour disease, a nasty transmissible cancer that has caused the rapid decline of wild devil populations in Tasmania. And until recently, scientists had hoped that Cedric held the key to the eradication of the disease.
Devil facial tumour disease (DFTD) was first reported in 1996, and since then it has wiped out about 90% of the wild devil population in Tasmania. It causes horribly disfiguring tumours that spread from the face to the rest of the body. The cause of DFTD was a real puzzle for a while — ‘contagious’ cancers are usually caused by viruses, but scientists couldn’t find any evidence of a viral cause. Eventually it was discovered that the cancers were being transferred from one devil to another through biting. Tasmanian devils are a bit scrappy and often have fights, biting each other on the face. Cancerous cells were being transferred in the bite wounds, and those cells then grew into parasitic tumours in their new host.
You would normally expect in this sort of situation that foreign cells would be rapidly attacked by the new host’s immune system. The problem with devils, though, is that they’re all quite closely related — they’re a small, inbred population. This means that they aren’t recognizing the new cancerous cells as foreign, and aren’t mounting an immune response — which allows the cancer to spread among the population.
The situation was looking rather dire for the future of the species, with the cancer rapidly spreading to devil populations across Tasmania, until scientists injected Cedric, who was born in captivity, with cancer cells. And Cedric mounted an immune response. His brother Clinky, however, wasn’t so fortunate. Both devils were injected with cancer cells, and only Cedric showed an immune response. Clinky developed the cancer while Cedric initially didn’t, and genetic testing showed that the two devils differed at the major histocompatibility complex (MHC) — an integral part of the immune response. It was hoped that studying Cedric’s MHC genes would provide some clues to help stop the spread of the facial tumour disease.
Unfortunately, Cedric did eventually develop a couple of small tumours on his face that were surgically removed in 2008. A few weeks ago it was found that he had developed more tumours in his lungs, and he was euthanized. His death is a huge disappointment to those who hoped that he held the key to eradication of the disease.
All is not lost, however, and scientists are hopeful that they will still be able to eradicate the facial tumour disease before it wipes out wild devils entirely. There is a population of devils in the north-west that appear to be resistant to the disease, so scientists are studying their immune systems in the hope of finding helpful clues to stop the spread of the tumours. Additionally, disease free devils are being bred in captivity just in case the disease does spread to the currently healthy populations in Tasmania.
Cedric’s death is a blow to conservationists, but it’s good to know that there is still hope for the future of Tasmanian devils.
Want to learn more about the fight to eradicate DFTD? Check out the Save the Tasmanian Devil program at http://www.tassiedevil.com.au/tasdevil.nsf