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Saturday, May 30, 2015

Tasmanian devils and their deadly transmissible facial cancer


Today's post is about a strange and horrid disease which you've possibly never heard about, unless you happen to live in Australia. It doesn't affect humans. Its unfortunate victims are Tasmanian devils.

The Tasmanian devil (Sarcophilus harrisii) is a carnivorous marsupial approximately the size of a small dog, with a stocky build, black fur and a keen sense of smell. These animals are solitary nocturnal scavengers that weigh up to 12 kg and generally live for 5 or 6 years in the wild. The island of Tasmania is the only place where a wild population of devils still survives - but, possibly, not for long. Since 1996, their numbers have become decimated by a nasty malady known as devil facial tumor disease (DFTD).

DFTD is a non-viral transmissible cancer which is spread by direct transfer of living cancer cells through biting. Infection can occur when animals fight with each other, e.g. during the mating season, or when an infected carcass is ingested.

The first signs of this disease are lesions and lumps around the mouth. They subsequently develop into large, soft, ulcerated cancerous masses which can spread from the face to various organs. Infected animals typically die within six months of organ failure, secondary infection or starvation, since the tumors make it difficult to ingest food. Scientists are working on a vaccine or cure, but without success. It is predicted that if no treatment for DFTD is found, Tasmanian devils could become extinct by 2035.

Genomic analysis suggests that the transmissible facial cancer first arose from a female Tasmanian devil and that the clone has subsequently become genetically diverse during its spread across Tasmania.

Below are the photos of two sick animals. Behold the unusual cancer that has survived beyond the death of the individual that spawned it by becoming adapted to transmission between hosts.





Literature:

Murchison EP. et al. (2012) Genome Sequencing and Analysis of the Tasmanian Devil and Its Transmissible Cancer. Cell. 148(4): 780–791.

Wikipedia: Devil facial tumor disease

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