Page last updated at 03:34 GMT, Friday, 1 January 2010

Tasmanian devil facial cancer origins 'identified'

By Mark Kinver
Science and environment reporter, BBC News

Tasmanian devil (Image: Anaspides Photography/Iain D Williams)
Since the mid-1990s, Tasmanian devil numbers have crashed

Researchers believe they have identified the source of fatal tumours that threaten to wipe out the wild population of Tasmanian devils.

Writing in Science, an international team of scientists suggest cells that protect nerves are the likely origin of devil facial tumour disease (DFTD).

The disease is a transmissible cancer that is spread by physical contact, and quickly kills the animals.

DFTD has caused the devil population to collapse by 60% in the past decade.

"To look more closely at the tumours' origin, we sequenced the genes that are expressed in this devil cancer and compared them with other genes that are expressed in other devil tissues," explained lead author Elizabeth Murchison, from the Australian National University in Canberra.

She told the Science podcast the team's findings delivered surprising results.

"We found that the tumours expressed genes that were normally only expressed by Schwann cells, which are cells that are found in the peripheral nervous system that protect nerves."

'Genetically distinct'

The researchers sampled 25 different tumours from all over Tasmania, the only place on the planet where the world's largest carnivorous marsupials are found.

Tasmanian devil (Image: Anaspides Photography/Iain D Williams)
Scientific name: Sarcophilus harrisii
Devils were given their common name by early settlers, who were haunted by "demonic growls"
Largest living carnivorous marsupial
Now only found in Tasmania
Can live up to five years in wild
Weight: male 10-12kg; female 6-8kg
They favour habitats where they can shelter by day and scavenge by night

They found that the growths were genetically distinct from their hosts, but were identical to one another.

Dr Murchison, who is also a researcher at Cold Spring Harbor Laboratory, US, said the teams findings had a number of positive outcomes: "Most importantly, this has led to the development of a diagnostic test for the disease.

"Devils are susceptible to a number of different types of cancer. Just like humans, they can get breast cancer, leukaemia, etc - especially in their old age.

"Sometimes it can be difficult to tell the difference between these types of cancer and the transmissible disease.

"Now that we know that these very specific Schwann genes are expressed in the cancer, we can use these genes as diagnostic markers."

DFTD was first described in the mid-1990s, when devils with large facial tumours were photographed in north-eastern Tasmania.

By the end of 2008, the disease - which kills infected animals within nine weeks - had been confirmed at 64 locations, covering more than 60% of the Australian island state's mainland.

Experts warn that without intervention, the disease could wipe out the wild population of the world's largest carnivorous marsupial within decades.

Dr Murchison hoped identifying the catalogue of genes associated with DFTD would lead to the development of vaccines, or possibly therapies.

Tasmanian devil with DFTD (Image: Save the Tasmanian Devil Program)
The disease usually kills infected devils within nine weeks

"As yet, unfortunately, there is nothing we can do to help the devils that have the disease," she said.

"This devil facial cancer is very unusual as it is an infection cancer; it is a little bit like an organ transplant," she said.

"In an organ transplant, you have an organ that is transplanted into an unrelated individual. In the case of the devil cancer, you have a cancer that is transplanted into another unrelated devil through biting.

"One of the big questions about this cancer is why it is not being rejected or being recognised as a foreign graft.

"If we could understand that... we could perhaps use this data to develop a vaccine that could help the devils' immune system reject the cancer before it takes hold."

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