Lethal Tasmanian Devil Tumors Spread by Contact, Study Finds
They are not considered cute or cuddly, but Tasmanian devils are a cultural icon of Australia, right behind koalas and kangaroos.
Over the last decade, however, devils have been dying off in massive numbers, felled by oral and facial tumors that prevent eating, causing them to starve to death. In some areas, virtually all of the animals have died from the mysterious disease.
A study by researchers at Tasmania’s Department of Primary Industries, Water and Environment now offers the first clues about how the disease is transmitted.
The study, published Thursday in the journal Nature, concludes that the animals are inadvertently transplanting tumor cells among themselves when they bite during fights and mating rituals.
The key came from an analysis of chromosomes in tumor cells, according to biologist Anne-Maree Pearse and her colleagues.
She found that chromosome patterns in tumor cells from the devils were identical to each other and grossly different from the devils’ healthy chromosomes.
The devils normally have six pairs of chromosomes plus a pair of sex chromosomes. In all of the tumor cells, however, both sex chromosomes were missing, as were both members of chromosome 2 and one member of the chromosome 6 pair. Moreover, a long section of chromosome 1 was missing and four new chromosome fragments were present.
Such a complex arrangement of chromosomes could not have occurred independently in each animal, Pearse concluded. Instead, the tumor must have arisen in one animal and subsequently been transferred to others when cells sloughed off during biting, allowing the tumors to take root in new animals.
Apparently, the devils’ immunological profiles are sufficiently similar that the tumor cells are not rejected. One piece of supporting evidence for this view is that devils in western Tasmania, which are genetically distinct from those in the east, have escaped the outbreak.
The best hope for fighting the outbreak is removing diseased animals from the wild, scientists believe.
Preliminary studies by biologist Menna Jones of the University of Tasmania in Hobart show that when all diseased animals are culled from a population cut off from other devils, the outbreak is halted.
