Devil Facial Tumour Disease

The seemingly needless “u” in “Tumour” is how it is written in reference to the disease, regardless of the country.

By Michael Hawkins

Devil Facial Tumour Disease is a particularly nasty cancer afflicting the Tasmanian devil population of Tasmania right now. It is spread by devils biting each other in the face and has been fatal for upwards of 50% of the population. Recent research has shed some light onto its origins.

Australian scientists found that the disease originates in Schwann cells, which protect peripheral nerve fibers. This has opened the door to the discovery of a genetic marker which can be used to diagnose the cancer.

What they also found was that in each subject, the disease was fundamentally the same. That is, the cancer does not originate in the individual devils, but instead comes from one common source, some long deceased devil. This means the disease can effectively be regarded as a separate organism, free to undergo its own evolution. Of course, its evolutionary ‘goals’ do not jive with the evolutionary ‘goals’ of its host, so there is an obvious conflict. (Please note the scare quotes around “goals”. The term is metaphorical.)

The cancer may become more and more virulent, allowing it to spread further and faster around the island. That could mean the end of both the devils and the cancer. Eventual death is not a very good long term evolutionary strategy, but then natural selection does not have any sort of foresight. Alternatively, the cancer could become less virulent so that its host could survive longer, thus offering the devil a greater chance to pass the disease along. Either way, the devils are out of luck.

One question this indirectly raises is if this susceptibility to cancer has anything to do with poor contact inhibition, the mechanism by which cells stop reproducing upon coming into contact with each other. Cells that don’t do that are called cancer. Most animals have one gene for this (p27), but naked mole rats have two (p27 and p16). This constitutes an extra barrier against cancer; as such, naked mole rats have never been observed to have developed cancer. Ever.

This means that at least one theoretical avenue of research into the cancer afflicting devils could be into the efficacy of their p27 gene: it may not offer the same effectiveness it does in other animals, especially considering the devil’s susceptibility to cancer in general.

But wherever the research should go, the dwindling Tasmanian devil population clearly needs help. And soon.

Devil cancer update

The devastating cancer spreading through the Tasmanian devil population has so far met resistance in at least one devil (Cedric), and possibly in his brother (Clinky).

Both were injected with dead tumours by scientists. Clinky produced no antibodies, but Cedric did and appears to have built-in defences against the mystery illness.

The experiments have now moved up a gear.

Researcher Alex Kriess says the pair have had live cancer cells inserted into their faces.

“They haven’t developed a tumour so far,” he said. “We injected very few cells so it might take a while until they develop anything that we can see.”

The next step is to see why Cedric may be resistant to the disease, which Jerry Coyne has deemed “can be regarded as a separate organism, genetically free to undergo independent evolution.” (The syntax is correct, but for clarity, it’s the disease that can be regarded as a separate organism.)

The most interesting aspect of all this is that Cedric comes from the side of the island not yet especially devastated by the disease. As more research is done, it will be interesting to find out if there is any sort of special history with cancer, even this specific cancer, that Cedric’s part of the island has had. That could be one driving cause behind the genetic difference to consider in addition to simple drift or geographical barriers.

Image via Jerry Coyne

Devil Facial Tumour Disease

Devil Facial Tumour Disease (DFTD) is a particularly nasty tumor currently afflicting Tasmanian devils. It is responsible for the destruction of around 70% of the island population. One step, fortunately, has been made through the discovery of its specific cause.

The research collaboration, led by Australian scientists, has found that DFTD originates from cells called Schwann cells, which protect peripheral nerve fibres.

The results have been published in the journal Science.

Through the discovery, the team has now identified a genetic marker that could be used to accurately diagnose the perplexing cancer, which has seen the devil listed as endangered and facing extinction.

What happens is that these devils – so appropriately named – tear into each others’ faces because, well, that’s what they do. They’re about as nasty as the tumor itself. This then transmits the disease from one animal to the next. The research, in fact, has shown that the tumors all share the same characteristics, thus showing that it’s essentially the same faulty genes that are getting passed around, not new, individual tumors. Once the disease is passed, a massive tumor grows on the face of the unfortunate devil. If it doesn’t die directly from the cancer first, it starves from its inability to eat with a massive growth all over its face.

Associate Professor Greg Woods from the University of Tasmania’s Menzies Research Institute said the Schwann cell find was an important step in the process to further understand the disease.

“Devils develop tumours of all different types and the genetic markers we have identified are useful for telling apart the tumours that occur in DFTD from other kinds of tumours,” Associate Professor Woods said.

The propensity for devils to develop cancer so easily is distressing. They’re like the anti-naked mole rats. I would specifically be interested in learning about the quality of contact inhibition of the devils. My suspicion is that it simply sucks.