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LAST Saturday (1 July 2006), two News Limited papers provided differing commentaries on the same scientific research paper on the devil facial tumour disease (DFTD).

Here’s what The Mercury [reporter Rohan Wade] wrote:

DOUBT ON HUMAN CAUSE OF DISEASE

Environmental factors appear unlikely to be causing the facial tumour disease affecting Tasmanian devils, a new research paper suggests. Authored by devil researcher Clare Hawkins, the paper says the disease appears to be infectious rather than a condition brought about by “human-induced modification of the environment or associated land use practices”.

The [Hawkins] paper stated this is on the basis of the disease’s apparently continuous distribution covering a range of land types and habitats.

“Both diseased and disease-free areas include national parks, agricultural and forestry areas,” [the research paper] stated.

Since research into the disease began there has been pressure for researchers to examine whether the use of chemical could be linked to the disease, and while the paper does not specifically rule out such a connection, the evidence of where the disease occurs suggests such a link is unlikely.

The Weekend Australian [reporter Matthew Denholm] wrote:

DEVIL NUMBERS CRASH AS DISEASE SPREADS

Several leading scientists believe DFTD was likely triggered when a single devil or a group of devils came into contact with carcinogenic chemicals, several of which have been used in farming and forestry. Devils were the victims of deliberate poisoning in the 1990s in the Mt William region, where DFTD first appeared in 1996.

Here is what the Clare Hawkins et al paper entitled: “Emerging disease and population decline in an island endemic, the Tasmanian devil, Sarcophilus harrisii” states:

The findings of the present study clearly indicate that DFTD is an emerging disease … prior to 1996, no devils were reported to manifest signs characteristic of DFDT,

It appears that DFTD is an infectious disease rather than a condition directly brought about by human-induced modification of the environment or associated land use practices, on the basis of its apparently continuous distribution covering a range of land types and habitats. Both diseased and disease-free areas include national parks, agricultural and forestry areas.

In October 2005, Matthew Denholm wrote a lengthy article in The Weekend Australian Magazine in which he interviewed DFTD cyto-geneticist, Anne Maree Pearse and government biologist, Nick Mooney.

Key scientists now believe that chemicals used by farmers or foresters triggered the disease. “That’s very likely: that in the first instance, the devil was for some reason or other exposed to a carcinogenic chemical,’ Pearse says.

There is no shortage of potential chemical culprits. “Take your pick,” Pearse says. “Organophosphates can cause genetic damage.”

Nick Mooney, a respected government wildlife biologist instrumental in getting DFTD taken seriously, agrees. Like Pearse, he is a key DFTD team member, and says the exposure of a lone devil, or a small group of devils, to chemicals was most likely the trigger.

“That is the likely scenario — that there isn’t ‘a’ chemical to blame, it’s more likely a group of chemicals, like organophosphates,” Mooney says. “And if that’s the case it will produce a very interesting public debate with some serious repercussions”.

Mooney believes the theory is more credible than the other possibilities — that an environmental pollutant, such as a herbicide or pesticide, or an exotic disease or pathogen, was the trigger.

Currently up to 53% of the area of occupancy for devils in Tasmania is DFTD-affected. In 1996 Menna Jones and Randy Rose published a report to the Tasmanian RFA in which they estimated the number of devils in Tasmania at between 130,000 and 170,000 individuals. Comparing distribution map of DFTD and Fig 1 (below) shows that the high density areas are the areas currently affected by DFTD.

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The Devil has the role of the hygienist scavenger/carrion feeder/predator in the Tasmanian ecology. As its Latin name suggests, it is a meat-lover. It is also known not to die from the consumption of wallaby and possum carcasses poisoned with the poison, 1080 (Sodium monofluroacetate). 1080 was first used in farming areas to control rabbits in the early 1950s and quickly became used to kill native wildlife, such as wallabies and brush-tail possums. Tasmania has used this poison continuously for the last half century, and I maintain that the high devil numbers calculated in the mid-1990s resulted from the artificial abundance of carrion across the areas of 1080 usage [agricultural and plantation forestry areas].

From the results of Anne Maree Pearse’s work and now Clare Hawkins, DFTD appears to be transmitted through direct devil-to-devil contact with high density populations suffering serious population declines.

The use of 1080 for crop and plantation protection would qualify as a “human-induced modification of the environment or associated land use practices”. If DFTD is shown to be a density-dependent condition the role of 1080 in abnormally growing the Devil population needs to be considered in the establishment and spread of this fatal disease. 

Work on exposure to synthetic chemicals and bioaccumulation of large number of frequently used chemicals needs to take place. As the top of the terrestrial food chain across Tasmania, the Devil is a prime candidate for both direct exposure and secondary bio-accumulation of chemicals from carrion feeding and predation on lower order animals.

In January 2005, the State Government promised to undertake test 10 to 20 toxins as possible environmental triggers for this disease. Dr Stephen Pyecroft, a vet with DPIW said chemicals could cause cancer by themselves or in combination with other factors. He said they could act as a catalyst that combined with genetic factors. “It’s been a thought on everyone’s mind that the cause could be a toxin.”  A DPIW report (January 2005) stated that samples from devils killed by the disease would be tested for pollutants and toxins. “If the toxins are there in significant levels, we have to look whether this is a cause or a trigger”, Dr Pyecroft said.

Last year Former PWS ranger at Mt William National Park, Steve Cronin, reported that up to 800 devils were killed through exposure to the highly toxic organophosphate, Phosdrin. This chemical has now been removed from use and the toxicological information on the active constituent — Mevinphos — notes its genotoxicity and capacity to induce mutagenic changes in test organisms. Other organophosphates besides Phosdrin have been used in Tasmania to indiscriminantly kill wildlife including eagles, harriers, ravens and quolls. Professor Jack Harrington, myself and Dr Neil McGlashan discussed the role of an environmental trigger for DFTD in the Australian Veterinary Journal last month.

I am concerned that the State Government is in control of the direction of the scientific investigation on DFTD; allowing some research to be funded and researched and other areas neglected or under-resourced.  Now that the Commonwealth government is contributing significant funds to this research program, I trust they will allow all research options to be investigated.

The Mercury

THE listing of the Tasmanian devil as a vulnerable species under federal law could have major ramifications on state forestry operations, the Tasmanian Greens say.

Read more here

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Picture: David Obendorf

Earlier: David Obendorf

David Obendorf

“That is the likely scenario — that there isn’t ‘a’ chemical to blame, it’s more likely a group of chemicals, like organophosphates,” Mooney says. “And if that’s the case it will produce a very interesting public debate with some serious repercussions”.