Cancers that can be transmitted between living beings are believed to be extremely rare. Australia's Tasmanian devils have long been known to suffer from contagious forms of the disease, making these marsupials an endangered species and threatening them with extinction.
With new reported cases in southeastern Tasmania, these animals are now plagued with a second strain of transmissible cancers. Scientists are aware that the discovery of this new strain changes how we perceive the infectious form of the disease.
The First Strain
About 20 years ago, several experts noticed that some of the Tasmanian devils in the northeast island of Tasmania were affected by tumors on their face and mouth. It was soon discovered that that the cancerous tumors were contagious between the animals and can be spread by biting.
Once spread throughout the body of the Tasmanian devil, the affected animal can die within months of the symptom's appearance.
The disease, which is called devil facial tumor disease (DFTD1), spread all over Tasmania and resulted in a decline in the population of Tasmanian devils. It wiped out 95 percent of the affected Tasmanian devil colonies in the area.
In 2008, these Australian marsupials were listed as endangered by the International Union for Conservation of Nature.
Two Other Known Forms Of Transmissible Cancers
Aside from DFTD1, scientists only know two other strains of transmissible cancers. These two strains affect soft-shell clams and dogs.
Conventional forms of cancer do not spread through contact, and do not survive beyond the body of the host who contains active cancer cells. Meanwhile, transmissible cancers are passed on between individuals through the transfer of living cancer cells.
The Second Strain
In a study featured in the journal Proceedings of the National Academy of Sciences, a team of experts from the University of Tasmania and the University of Cambridge identified the second strain of genetically transmissible cancer in eight Tasmanian devils.
The new disease, dubbed DFTD2, was discovered last year by Dr. Ruth Pye of UTAS in a devil sampled in the D'Entrecasteaux channel area, south of Hobart.
"The second cancer causes tumours on the face that are outwardly indistinguishable from the previously-discovered cancer," said Pye.
Dr. Elizabeth Murchison of Cambridge, a transmissible cancer expert, confirmed that the new strain is now the fourth known found in nature. The new strain is changing the current perception about transmissible cancers, and is making scientists wonder whether transmissible cancers are not really rare in nature.
Tasmanian Devils May Be Particularly Susceptible
Researchers previously thought that Tasmanian devils were unlucky to fall into a single runaway cancer that spread from one individual to another.
Now that there was a second strain, Murchison said it was curious if perhaps Tasmanian devils are especially vulnerable to developing this kind of disease.
Professor Gregory Woods, one of the researchers of the study, explained that in the Tasmanian wilderness, there must be more transmissible cancers in devils – new strains that have not been discovered yet.
"The potential for new transmissible cancers to emerge in this species has important implications for Tasmanian devil conservation programs," said Woods.
Vaccination For DFTD1
Woods and Pye are part of a team that developed vaccines against DFTD1. Testing of the vaccine started earlier in 2015. Woods hopes DFTD2 could be similarly managed.
"Fortunately this is similar to DFTD1 and the procedures in place to deal with DFTD1 will be used to investigate this new cancer," said Woods.
He said a vaccine for the new strain will be incorporated into their current vaccine research.
What Does This Mean For Humans?
Pye and her colleagues said the transfer of cancer cells between two humans have been reported in rare situations such as organ transplantation, injury, pregnancy and experimental treatments. However, there have not been any cases of naturally transmitted cancer occurring between two or more human hosts.