Tasmanian Devil are flattening the curve and likely to survive cancer fight

December 27, 2020
Animal
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Image Source: https://www.smh.com.au/

The Tasmanian Devil has flattened the curve of the spread of the transmissible cancer that has threatened it with extinction and new evidence is suggesting that due to the animal’s rapid evolution it is likely to survive the disease.

Using similar sophisticated methods of genomic analysis used to trace the evolution and spread of COVID-19 through human populations, scientists have established that the reproduction number of the disease has significantly reduced.

The research, published on Friday in the leading journal Science, shows when the disease first emerged in the late 1990s each infected animal passed the facial cancer tumours on to an average of 3.5 other devils, which is a higher reproduction number than for COVID-19, which has a reproduction number of around 2.32.

According to the research due to rapid evolution in both the surviving population of devils and in the two lineages of the cancer itself, that number has fallen to just under one.

There is also evidence of devils surviving the disease which was thought to be universally fatal at its height, with some contracting the cancer and later recovering.

Should the reproduction number remain below one for long enough the disease may eventually burn itself out or come to exist endemically in the devil population says one of the paper’s authors, Professor Hamish McCallum of Griffith University.

The population of the animal has crashed from an estimate of over 60,000 when it was first identified in 1996 to under 10,000 in the wild today and devil facial tumour disease, or DFTD has spread across the state but for a handful of small remote sites.

Professor McCallum said there was some evidence the disease had waned and then surged in some parts of the state over the years, and that it was hoped it might slowly start to recover. However, with so few breeding pairs the species was still vulnerable to extinction.

The research, based on analysis of samples taken from devils in the wild across Tasmania since the early 2000s reinforces earlier research published by the same team based on mathematical modelling.

“The thing which I find most encouraging is when you have multiple lines of evidence pointing in the same direction,” Professor McCallum said. “This is the icing on the cake.”

Another of the paper’s authors, genomics specialist Professor Andrew Storfer of Washington State University said there was evidence that lower devil populations and changing behaviour was also slowing the disease’s spread.

The disease is spread by the devils nipping at one another while competing for food and mates, but when sick they fall out of that “contact network”, further slowing infections.

Story Source: https://www.smh.com.au/environment/conservation/tasmanian-devil-are-flattening-the-curve-and-likely-to-survive-cancer-fight-20201211-p56mox.html

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