For such a foul-tempered, ferocious and smelly creature, the Tasmanian devil is beloved in its native Australia, where it is considered a symbol of the country's frontier toughness. (The dog-sized marsupial's second life as a Looney Tunes character hasn't hurt its popularity either.) But as fierce as it is, the devil which is found only in the Australian island-state of Tasmania is in danger of going extinct.
It's not an issue of predators or hunters the devil can handle them but of a peculiar, transmissible disease. Devil facial tumor disease (DFTD) causes tumors to form in and around the mouth of infected devils; the tumors eventually grow so large that they prevent the animal from feeding and lead to starvation. First discovered in 1996, the cancer has spread swiftly through the Tasmanian devil population, killing more than 70% of the island's animals. If nothing is done to stop the disease, the devils could go extinct within 35 years.
But new research on the origins of the fatal cancer suggest that methods for rapid diagnosis and even a vaccine against the disease may be possible. Reporting in a paper published in the Jan. 1 issue of Science, an international team of researchers based in Australia and New York State performed a genetic analysis of DFTD and found that it likely began in the devil's Schwann cells, a type of tissue that protects nerve fibers. Researchers have also identified genetic markers for the disease, which should allow doctors to distinguish facial tumor disease easily from other cancers that afflict the Tasmanian devil, and could eventually help determine a genetic pathway to attack the tumor itself. "This is the first application of genetics to estimate the basic biology of the tumor," says Tony Papenfuss, a bioinformatics researcher at the Walter and Eliza Hall Institute of Medical Research in Melbourne and a co-author of the Science paper. "And we've produced a set of tools that can push that information further."
DFTD is a virtually unique cancer in that it is spread from animal to animal via biting or other physical contact one of only three cancers that are thought to spread this way. While some human cancers can be linked to transmissible pathogens such as cervical cancer, which is caused by the human papillomavirus in DFTD, infected devils actually transmit the tumor itself to other devils when they bite.
Through genetic analysis, the Science team was able to confirm that the tumors being spread from devil to devil were the same genetically identical, exact clonal copies. Using genetic sequencing technology, the team also uncovered the tumors' transcriptome, which means the set of genes that are activated in tumors. Those activated genes best matched those of Schwann cells, which gave the team a clue as to where the disease originated that's important because devils are unusually susceptible to a number of different cancers, and a quick diagnosis before the facial tumors get out of control would be helpful. "The real importance of this is that we can differentiate between the facial tumor disease and any other cancer," says Papenfuss. "That allows for much more specific diagnoses."
Better diagnoses may lead to more targeted prevention efforts. Right now the only way to slow the spread of the disease is simply to separate healthy devils from infected ones. Naturalists are creating "devil's islands," cancer-free areas in Tasmania where healthy devils can live and breed. But that alone may not be enough to save the animal the Tasmanian Conservation Trust recently warned that there were not enough healthy devils in captivity to ensure a viable population. "It's critical that we find something to help save them," Elizabeth Murchison, the lead author on the paper, told Science in an interview.
The devils will eventually need a vaccine, and there is hope that this research may help scientists develop one. The team compiled a catalog of devil genes that affect the tumor and may contribute to its growth; these could be useful targets for designing a future vaccine. The difficulty will be creating a treatment that attacks the tumor, but spares healthy cells. "The key in a vaccine is not to create immune action that would hurt the devils by attacking their Schwann cells," says Papenfuss. "Now we can look for specific markers on the tumor cells to attack." Tough as they are, Tasmanian devils still need a lot of help.