In an indication that transmissible cancer may not be as rare as generally believed, researchers have identified a second, genetically distinct variety in Tasmania devils, iconic small dog-sized carnivores that are only found in the wild on the Australian island state of Tasmania.
Scientists had earlier discovered one form of transmissible cancer in the devils that causes them facial tumours.
"The second cancer causes tumours on the face that are outwardly indistinguishable from the previously-discovered cancer," said study first author Ruth Pye from University of Tasmania, Australia.
"So far it has been detected in eight devils in the south-east of Tasmania," Pye noted.
Transmissible cancers -- cancers which can spread between individuals by the transfer of living cancer cells -- are believed to arise extremely rarely in nature.
"Until now, we have always thought that transmissible cancers arise extremely rarely in nature, but this new discovery makes us question this belief," senior author on the study Elizabeth Murchison from University of Cambridge, noted.
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In 1996, researchers observed Tasmanian devils in the north-east of the island with tumours affecting the face and mouth; soon it was discovered that these tumours were contagious between devils, spread by biting.
The cancer spreads rapidly throughout the animal's body and the disease usually causes the death of affected animals within months of the appearance of symptoms.
The cancer has since spread through most of Tasmania and has triggered widespread devil population declines.
To date, only two other forms of transmissible cancer have been observed in nature: in dogs and in soft-shell clams.
The discovery of the second transmissible cancer in Tasmania devils began in 2014, when a devil with facial tumours was found in south-east Tasmania.
Although this animal's tumours were outwardly very similar to those caused by the first-described Tasmanian devil transmissible cancer, the scientists found that this devil's cancer carried different chromosomal rearrangements and was genetically distinct.
Since then, eight additional animals have been found with the new cancer in the same area of south-east Tasmania.
The findings appeared in the journal Proceedings of the National Academy of Science (PNAS).