tasmanian devil

SYDNEY, Australia (AP) ― Australian researchers have made a breakthrough discovery in understanding a rapidly spreading facial cancer that has decimated the country's Tasmanian Devil population.

A lack of genetic diversity in the fierce, fox-like creatures has meant the animals' immune system does not try to fight off the disease, spread through biting, according to a study by the University of Sydney's School of Veterinary Science released last week.

The grotesque facial tumors were first spotted in the devil population around a decade ago in the northeast of Australia's island state of Tasmania, where 90 percent of the species has died of the disease.

The affliction is spreading south and west, and scientists estimate that within five years, there will be no disease-free population in Tasmania ― the only place in the world where the carnivorous marsupials exist outside zoos.

Seeking to understand how a facial cancer could be contagious, the University of Sydney researchers found that the tumors had originated from a single cell line that was spread through the population by biting.

Because Tasmanian devils are genetically similar, their bodies do not recognize the tumors as foreign cells and do not produce an effective immune response.

"We propose that this tumor arose in a single individual and has spread through the population by biting during fights for food and mates," lead researcher Katherine Belov said in a statement.

"Essentially, there are no natural barriers to the spread of the disease, so affected individuals must be removed from populations to stop disease transmission," she said.

Scientists estimate that the wild devil population has fallen from around 140,000 in the 1990s to 80,000 in 2006 due to the spread of the tumors, which ― by making it difficult for the animals to bite and catch prey ― usually lead to their death from starvation within six months.

Experts fear the remaining healthy animals could become extinct within the next two decades if they are not isolated from the disease.

Since the disease first emerged, scientists have been working to save the endangered marsupials, known for their powerful jaws and bloodcurdling growl. Programs to try to save them include plans to relocate breeding pairs to island sanctuaries.
Warning: Graphic content More evidence, if it were needed, that no good can come of indulging in cousin-coitus. The Tasmanian devil, the grouchy doglike marsupial immortalised in the form of Warner Bros character Taz, is facing extinction due to a rampant communicable cancer.


The gruesome effects of DFTD.
Researchers have concluded that the rapid spread of the cancer, which has halved the devil population in just over a decade and may obliterate it altogether in another, is due to a lack of genetic diversity.

The flourishing Devil Facial Tumour Disease (DFTD) seems to pass easily from one animal to another during fights over food and mates. The devils are generally free with their teeth in such skirmishes, but the smallest of wounds to the mouth can result in death within six months as the cancer takes hold. Tumours sprout around the head and face, sometimes displacing eyes and teeth, and make it impossible for the animals to feed, inevitably leading to death from starvation.

The disease is one of only two known naturally-occurring infectious cancers - dogs and other canines can contract Canine Transmissable Venereal Tumour (CTVT) through copulation, but it is by no means always fatal.

Scientists have been struggling to find out the secret of DFTD's success in killing devils, whose population has fallen to around 75,000 from 150,000 in 1996. A collaborative project between the Sydney and Tasmania Universities, published this week online in the journal Proceedings of the National Academy of Sciences (pdf here), has made the breakthrough discovery that the devils' immune system - unlike that of dogs suffering from CTVT - simply does not fight the cancer because of a lack of genetic variation within the population.

The most important immune system gene region, the Major Histocompatibility Complex (MHC), has lost its healthy diversity in Tasmanian devils over time - the MHC of the tumour corresponds too well to that of the infected animals for their system to be inclined to combat it.

This means that otherwise robustly healthy animals can succumb quickly to DFTD, since their bodies do not recognise it as a threat. Rather, the cells are embraced by the animal's system as their own - the cells in all infected devils are genetically identical, making contraction of the cancer more like a sort of malign transplant.

A "Noah's Ark" project should ensure the survival of the species, with disease-free "insurance populations" being bred in safe areas. In theory, when DFTD is extinct the healthy colonies can be reintroduced - however, the ecological impact of the devils' rapid disappearance from the wild may be dire. They may not be as cute as koala, as iconic as kangaroos, or as just-plain-weird as the platypus but Australia would still be a poorer place without the Tasmanian Devil. Sadly the devil is headed for extinction within five years, decimated by a deadly, infectious facial tumour (The Age, ABC, AAP, Tasmania's Mercury). Research has now uncovered why the animals have no immune response at all to the tumours � genetic diversity in a key set of genes is so low that the devils' immune systems do not recognise the tumours as foreign.

The research, published online in PNAS, shows that the tumours are actually clonal cell lines � a tissue graft being passed from one animal to another when they bite each other in fights or during mating (abstract, pdf). "We found that the Devils do not mount an immune response against the tumour," says author Katherine Belov from Sydney University's School of Veterinary Science (press release).

"This was due to a loss of genetic diversity in the most important immune gene region of the genome: the Major Histocompatibility Complex (MHC). Matching of MHC genes is the key to successful tissue or organ transplants. In the case of the devil, genetic diversity at MHC genes is so low, and the MHC type of the tumour and host are so alike, that the host does not see the tumour as 'non-self'."

On the plus side isolated populations of devils might have different MHC genes, and be able to fight the tumour (Mercury). The finding might help stop the spread of the disease, but it's bad news for those already infected. "Essentially, there are no natural barriers to the spread of the disease, so affected individuals must be removed from populations to stop disease transmission," said Belov (press release).

The Sidney Morning Herald last month noted that a set of healthy animals has been sent to zoos and sanctuaries on the mainland under the auspices of the imaginatively titled 'Project Ark'. The UK's Independent has picked up on this and provides a remarkable example of how similarly journalists think noting: "Less cuddly than the koala, less quirky than the kangaroo, the Tasmanian devil is not everyone's cup of tea." But you'll miss them when they're gone... Australian scientists say the ongoing fight to save Tasmanian devils from extinction may be doomed.

Researchers have been battling to find a cure for a deadly facial tumor disease that has decimated the numbers of the rare animals -- found only in Australia's island state of Tasmania.

But now scientists at Sydney University have suggested a lack of genetic diversity because of inbreeding will doom the devils in any case.

Geneticist Kathy Belov, leader of the university scientific team, told the Australian Broadcasting Corp. the devils had been found to have "very low levels of genetic diversity in really key immune genes."

"What this means is that they are going to be susceptible, not only to this horrible cancer that is decimating them at the moment, but potentially to all sorts of other diseases, because they simply don't have the genetic diversity in their genes, which will enable them to respond to any new diseases that are thrown at them," she said.

A deadly facial cancer already has killed half of the devil population because the animals have no resistance to the disease which they catch from biting each other -- fighting over food or mates at breeding time.

Belov said even though scientists hoped to save the Tasmanian devil from extinction through breeding a captive "insurance" population, it would be hard to protect them from any epidemic in the future.

Copyright 2007 by United Press International. All Rights Reserved.