Scientists probe CWD's spread through soils
 t is challenging enough to eradicate deer populations
in areas thought to harbor Chronic Wasting Disease (CWD), the mysterious
neurological deer and elk illness that is cropping up in unexpected
places, such as New York.
But once state officials have killed hundreds of
deer, what if infectious prions—the elusive proteins thought to
cause CWD—remain in deer carcasses, eventually seeping through
garbage landfills and draining uncontrolled into wastewater treatment
plants and beyond?
With backing from the Environmental Protection Agency,
UW-Madison scientists are investigating the potential scenario. They
reported early findings during the International Chronic Wasting Disease
Symposium here on July 12-14.
Recent evidence suggests that prions have a tendency
to latch onto soil particles. Since deer eat soil at certain times of
the year, scientists have surmised that CWD-inducing prions might piggyback
into the animals through ingested earth. But can those prions make their
way into soil at a dumpsite?
To understand the potential risks in disposing of
deer carcasses in landfills, environmental biochemist Joel Pedersen,
virologist Judd Aiken and geo-environmental engineer Craig
Benson are trying to simulate a “mass waste” situation
in the laboratory. “[Landfills] are a really, really complicated
system, so we are starting out simple, with just a pure column of sand,”
says Pedersen. The UW-Madison researchers found that prions did indeed
leach, or drain down, through the sand particles. “We are currently
evaluating leaching through soils commonly used in landfills and will
soon be working with synthetic municipal waste and real municipal waste,”
Pedersen adds.
It’s hard tracking prions, not least because
researchers know hardly anything about them. Completely unlike bacteria
and viruses, prions “don’t conform to the paradigm of what
we know to constitute infectious diseases,” says Assistant Professor
Trina
McMahon, who also spoke at the CWD meeting.
McMahon’s piece of the puzzle begins where
fluids from landfill sites course into wastewater treatment plants.
She is exploring how prions would behave if they were to flow from landfills
into the wastewater treatment process. “This is a waste containment
issue,” says McMahon. “If prions remain in solid form, we
can probably contain them, but if they get into liquid they would be
much more mobile.”
When sewage flows into wastewater treatment plants,
it runs first into a tank filled with natural bacteria. The organisms
essentially break down the incoming waste, which eventually separates
into clean water and “waste activated sludge,” a combination
of bacteria and the sticky, slimy goo it exudes. In early laboratory
simulations, McMahon found that prions—which are sticky themselves—latch
onto the bacterial goo and remain infectious.
In later stages of wastewater treatment, the sludge
is processed into a purified and nutrient-rich organic material known
as a biosolids. Scientists have long urged farmers to spread the substance
on their fields but the practice remains controversial, says McMahon.
The researcher intends to spend the next year ascertaining
whether prions eventually wind up in and remain infectious inside bio-solids.
Her results could heavily sway the fate of the material’s use
in agriculture.
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