Dog cancer find may help Tassie devils
A GENETIC STUDY into an infectious dog cancer may shed light on the Tasmanian devil facial cancer.
There are only two known cancers that are infectious and capable of being passed between individual animals. Tasmanian devil facial tumour disease (DFTD) is well known to Australians and has been decimating populations of the marsupial carnivore since it first appeared in the 1990s.
The other is a sexually transmitted cancer of dogs called transmissible venereal tumour (TVT), which has been known about since at least the 1800s.
An international team of researchers led by Dr Elizabeth Murchison, an Australian at Cambridge University in the UK, has now sequenced the genome of TVT. Their results suggest the cancer first arose in one dog 11,000 years ago and has ever since been able to spread from dog to dog across the world.
A parasite and a transmissible cancer
As detailed today in the journal Science, the researchers collected samples of the cancer from a dog in Brazil and an Aboriginal camp dog from the Northern Territory.
“Using samples from different places in the world, you can acquire something like a ‘family tree’ of the tumour,” says veterinarian Dr Ted Donelan, study co-author at Animal Management in Rural and Remote Indigenous Communities (AMRRIC), a charity in Darwin, NT.
Similar to the Tasmanian devil facial disease, the dog cancer acts as a parasite, moving from host to host via direct contact. However, it is sexually transmitted, growing on the genitals, and the polygamous mating habits of dogs work in its favour.
While TVT causes distress for dogs and their owners, it is not as aggressive as its Tasmanian devil counterpart. It responds well to chemotherapy and can go into remission naturally.
“It’s a more slowly developing tumour than the one found in Tasmanian devils,” says Ted. “The main difference is that it doesn’t kill dogs so quickly.”
This is thought to give the dog tumour an edge in longevity, because the host lives long enough to be able to pass it on.
Dog cancer sheds light on Tasmanian devil disease
“The hope is that work on the dog cancer will shed light on the devil one,” says Professor Hamish McCallum, a Tasmanian devil expert at Griffith University in Brisbane who was not involved in the study.
He says that DFTD may be so aggressive and kill so many Tasmanian devils, because it has only appeared very recently – perhaps in the last few decades. The dog cancer has had much longer to hone its evolutionary strategy and develop ways to keep its hosts alive long enough to be passed on.
The study of these infectious cancers raises interesting questions about cancer in general.
“A tumour normally lives only as long as its host,” Hamish says. “These transmissible cancers [are] obviously something that can happen in nature, so why is it so rare? If we understand that, we will understand more about cancer in general.”
