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Infectious cancer may be killing devils

Devil with facial tumour

Facial tumour disease can leave the face of Australia's carnivorous marsupial looking "like pizza", researcher Anne-Maree Pearse says (Image: Christo Baars)

The mysterious facial tumour disease ripping through Australia's Tasmanian devil population may be an infectious cancer spread by biting, a researcher says.

Anne-Maree Pearse of Tasmania's Department of Primary Industries, Water and Environment reports in the journal Nature today that the tumour cells are chromosomally identical despite being found in different animals, suggesting the existence of a "rogue cell line".

"The thrust of my theory is that a cell line developed in a cancer in a devil somewhere, some time," she says.

"This cell line became persistent and basically had an existence of its own ... and is just passing through the population like an epidemic."

Pearse says during fights mutated tumour cells may break away from the ulcerated tumour of a diseased devil and become "transplanted" into a healthy devil, where they form the seed of a new tumour.

"We propose that the disease is transmitted by allograft, whereby an infectious cell line is passed directly between the animals through bites they inflict on one another," she writes.

Facial tumour disease, which first became apparent in the mid 1990s, is now present across more than half of the southern island state and has cut the Tasmanian devil (Sarcophilus harrisii) population in some parts by up to 80%, according to the Tasmanian government.

Genetic bottlenecks

Pearse says devils may be particularly susceptible to the disease because of genetic bottlenecks caused by past population crashes.

The crashes resulted in a loss of genetic diversity, which may have caused a net weakening of the devil's immune defences, she says.

Her colleague Dr Menna Jones, a conservation biologist from the University of Tasmania, says the cell line transmission theory is backed by her own research, done with Rodrigo Hamede, into devil fighting and biting behaviour.

"Given what we know about the ecology and behaviour of devils, if you're going to pick any species that might transmit any pathogen or disease by biting, devils would be a very likely candidate," Jones says.

The theory comes as good news for those involved in combating the disease, she says.

"What's nice about the allograph theory is that it does make disease suppression or disease control simpler," she says.

"If transmission is simply transfer of tumour cells from devil to devil ... the most effective thing you can do is simply to take sick animals out of the population."

Jones says the research comes as the Tasmanian government prepares to launch a two-year disease suppression study in the state's southeast following a successful pilot last year.

The study will monitor the impact of isolating an estimated 300-400 devils that live on Tasmania's Forestier and Tasman peninsulas, where the disease hasn't yet established a stronghold. They will be separated from the mainland with devil-proof grates.

Can it spread to humans?

Pearse, who also has a background in human cytogenetics, says studying devil facial tumour will advance understanding of cancer in humans.

She says there's no human equivalent of a transmissible cancer but there have been cases where organ transplant patients have developed cancer if cells were hidden in the donor organ.

She says it's highly unlikely devil facial tumour disease could spread to other species, including humans, but this will be the subject of future research.

Tags: environment, zoology