Could Plants Spread CWD to Animal Life?

By Todd Wilkinson, The New West
 

"It is highly unlikely that CWD will spread naturally to the greater Yellowstone area from the endemic area [in southeast Wyoming]."

-Letter written by the late state wildlife veterinarian Tom Thorne, then acting director of the Wyoming Game and Fish Department, to conservationists on May 28, 2002.

How long before the deadly brain disorder chronic wasting disease - the deer family equivalent of mad cow disease - reaches the wildlife-rich heart of the greater Yellowstone ecosystem, home to some of the most famous ungulate herds in the world?

Hindsight can be 20/20. Contrary to what the late Tom Thorne claimed 13 years ago, CWD-infected wildlife is showing up in western Wyoming hunting units.

Each year afflicted animals come closer to Wyoming's 22 elk feedgrounds and the U.S. Fish and Wildlife Service's National Elk Refuge in Jackson Hole. Will western Wyoming soon become a springboard for CWD proliferating into Montana and Idaho?

Now scientific research into possible vectors of CWD transmission suggests a number of previously unrecognized routes for wildlife infection.

A Texas study and another from the U.S. Geological Survey in Wisconsin indicate that not only can CWD prions be absorbed into plants, but they potentially can infect mammals grazing on them.

Earlier studies confirmed that CWD-infected animals can contaminate soils where they live with prions shed into the environment via fecal matter, bodily fluids and decomposing tissue. In fact, captive Wyoming elk kept in a state research pen where other wapiti died from CWD also contracted the disease and perished after being exposed merely to tainted soil.

Where speculation becomes hair-raising, especially when considering how prion diseases could jump species barriers and pose a threat to humans, is in the variety of plants found by scientists that can absorb prions.

"Grass plants can bind, uptake and transport infectious prions," Dr. Claudio Soto and colleagues at UT Health in Houston revealed recently in the journal Cell Reports.

"This suggests that plants may play an important role in environmental prion contamination and the horizontal transmission of the disease," Soto and researchers wrote.

Chronic wasting, known to strike deer, elk and moose in 22 states, is among a family of incurable diseases classified as "transmissible spongiform encephalopathies." The list includes Mad Cow in cattle, variant Creutzfeldt-Jakob in humans and scrapie in sheep.

The diseases attack the brains of victims and render them incapacitated.
"There is no proof of [CWD] transmission from wild animals and plants to humans," Soto wrote. "But it's a possibility that needs to be explored and people need to be aware of it. Prions have a long incubation period."

A study led by Christopher Johnson at the USGS lab in Madison, Wisconsin, demonstrated that plants growing from CWD-contaminated soils could spread the disease.

Johnson discovered that prions could be absorbed into alfalfa, barley, tomatoes and corn. In turn, when CWD prions were extracted from plants and injected into mice, the rodents became ill.

"Our results suggest that prions are taken up by plants and that contaminated plants may represent a previously unrecognized risk of human, domestic species and wildlife exposure to CWD and scrapie agents," Johnson wrote in a 2013 abstract.

That comes on top of other insights, one being that hard-to-destroy prions bind with soil and can become up to 680 times more infectious when ingested orally.

Lloyd Dorsey, conservation director for the Sierra Club's Wyoming Chapter, has been doggedly tracking CWD in Wyoming for two decades.
Dorsey asks: What if CWD reaches thousands of elk bunched together on winter feedgrounds and it then becomes established in grasses and soils?
He believes that by continually downplaying warnings, state and federal agencies are unprepared to deal with the consequences of unnaturally congregating wildlife herds in winter that then disperse throughout the northern Rockies in summer.

Wyoming, Dorsey notes, has more CWD cases in elk and deer and more land affected and at risk from the disease than any other state in the country. Apart from animal-to-animal transmission, the Texas and Wisconsin studies show just how insidious the possible avenues for spreading CWD might be.
"Denial never serves the public's interest," Dorsey says. "We should be in an action mode to mitigate the effects of this potentially catastrophic disease we know is coming."