Sludge Watch ==> Clues on how CWD spreads - some soil types more high risk

[Maureen Reilly]

Admin: How about the EPA approved policy of  topdressing  sewage sludge 
which may contain both human and animal prions on dairy pastures, hay fields 
and grazing lands ?


"Aiken agreed. "You have an infective agent that doesn't degrade easily," he 
said. "It's not going to percolate through the soil. It's going to bind."

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http://www.madison.com/wsj/home/local/index.php?ntid=200272&ntpid=2


FRI., JUL 6, 2007 - 10:00 AM
Finding offers clues on CWD
RON SEELY
608-252-6131
rseely at madison.com
By binding to a common soil mineral, the misshapen proteins that cause 
chronic wasting disease in deer can be as much as 700 times more infectious 
than exposure to the proteins alone, according to researchers at UW-Madison.

The finding, by UW-Madison animal health and biomedical science professor 
Judd Aiken, may help explain why CWD spreads orally among Wisconsin deer 
even though animals in the wild are exposed to relatively low levels of the 
infectious proteins, called prions.

Herbivores, including deer and sheep, consume a fair amount of dirt each day 
as they graze. They are also known to consume soil as a source of minerals.  
     [grazing cattle are known to ingest 1 kilogram of soil a day 2.2 pounds 
- ]

The study would appear to support efforts by the state Department of Natural 
Resources to slow the spread of chronic wasting disease by thinning the size 
of the herd and thus reducing the number of infected animals releasing 
prions into the landscape. Previous studies have shown the infectious prions 
are present in saliva and other body fluids in sick deer.

"Reducing the number of animals that are releasing the infectivity is a 
clear and logical response," Aiken said.

The research was published today in the journal Public Library of Science 
Pathogens.

Prions are abnormal proteins that cause CWD by prompting healthy proteins to 
morph into the more deadly variety. Animals die when the prions build up in 
the brain and cause massive lesions. The fatal brain disease was discovered 
in the Wisconsin deer herd more than five years ago, and of 129,539 deer 
tested, 856 have been found to have the disease, all in southern Wisconsin. 
So far, no connection between CWD and human illness has been uncovered.

But researchers have been perplexed by how the disease spreads among deer in 
the wild, especially because deer do not seem to be exposed to high levels 
of the prions such as the levels that would appear in infected meat.

The study by Aiken and Joel Pedersen, a UW-Madison professor of soil 
science, looked more closely at a phenomenon that had been hinted at by past 
experiments -- that prions that cause CWD seem to linger in, and be spread 
partly through, soil.

The researchers studied how prions interact with a common soil mineral 
called montmorillonite, generally found in clay soils. Aiken said he and 
Pedersen were shocked at how tightly the stubborn prions bound to the 
mineral and finally found they had to boil the soil in detergent to get them 
off.

But it was when the researchers fed the prion-mineral mix to hamsters in the 
laboratory that they made their most surprising finding. The scientists 
expected to see a lower rate of infection than in animals fed just the 
infectious protein and not the mineral. Instead, the prions bound to the 
montmorillonite were far more infectious. The difference was huge, according 
to Aiken, with the prion-mineral mix being nearly 700 times more infectious.

Just why this is so remains a mystery and will be the subject of further 
research. But Aiken and Pedersen speculated that the soil particles may 
protect the prions from breaking down in the digestive tract. Other 
possibilities, according to the scientists, are that the clay-bound prions 
are more easily taken up into a deer's digestive system or that the mineral 
causes more clumping of prions into aggregates, which are more infectious 
than single prions.

Alan Crossley, who oversees the DNR's battle against CWD, said the finding 
will be important as the DNR begins working with hunters and others to 
evaluate the effectiveness of the agency's control efforts. The research 
would seem to show, Crossley added, that the agency is following the correct 
course by reducing the number of deer and, therefore, the number of deer 
that could spread the disease.

"When you start getting higher prevalence," Crossley said, "the likelihood 
of the soil being a reservoir is greater."

Aiken agreed. "You have an infective agent that doesn't degrade easily," he 
said. "It's not going to percolate through the soil. It's going to bind."