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Prions — the infectious, deformed proteins that cause chronic wasting disease in deer — can be taken up by plants such as alfalfa, corn and tomatoes, according to new research from the National Wildlife Health Center in Madison.

The research further demonstrated that stems and leaves from tainted plants were infectious when injected into laboratory mice.

The findings are significant, according to the researchers and other experts, because they reveal a previously unknown potential route of exposure to prions for a Wisconsin deer herd in which the fatal brain illness continues to spread. The disease has also become a pressing issue nationwide: The national Centers for Disease Control and Prevention has identified the deer disease in 17 states and predicts it will spread to other states.

In Wisconsin, where the state Department of Natural Resources has scaled back its efforts to slow the spread of CWD, some critics say the new research should cause the agency to revisit its approach.

Michael Samuel, a CWD researcher and wildlife ecology professor at the University of Wisconsin-Madison who was not involved in the plant research, said the new study is significant. Previous studies have shown the disease can be transmitted animal-to-animal and via soil.

“It’s important because it identifies a potential pathway,” Samuel said of the study.

Christopher Johnson, who conducted the study, wrote in the abstract: “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.”

The research has not yet been submitted for publication in a scientific journal.

The study focused on those prions similar to those causing CWD in deer.

The disease is one of a class of neurological, prion-caused diseases known as transmissible spongiform encephalopathies, including scrapie in sheep and goats, bovine spongiform encephalopathy — or mad cow disease — in cattle, and Creutzfeldt-Jakob disease in humans. CWD was discovered in Wisconsin’s deer herd in 2002 and has been found since the mid-1990s in northeastern Colorado and southeastern Wyoming.

Johnson is scheduled to present his research at the annual meeting of The Wildlife Society in Milwaukee in October. Johnson studies CWD at the federal wildlife disease center, which is run by the U.S. Geological Survey. His earlier work found CWD prions can linger in and be amplified and transmitted by soil.

‘Major review’ needed?

James Kazmierczak, the state public health veterinarian, said that a molecular species barrier, though little understood, appears to have so far prevented the CWD prions from making people and cattle sick.

Also, Kazmierczak said, data reported to the Wisconsin Division of Public Health show little deviation from the national rate — a little above one case per million people — in annual cases of Creutzfeldt-Jakob Disease. Nor, he added, does data on more than 800 Wisconsin hunters who have consumed CWD-tainted venison show any human cases of prion brain disease.

Nationwide, according to the CDC, “no strong evidence of CWD transmission to humans has been reported.”

Even so, the threat of CWD transmission by crop and food plants — and the newly discovered potential for exposure to humans and livestock — has prompted some to say the state Department of Natural Resources should reconsider its CWD policy.

“That is very disconcerting,” George Meyer, executive director of the nonprofit Wisconsin Wildlife Federation, said of the research.

“My impression,” said Meyer, a former DNR secretary, “is (that) it should cause a major review of the very weak CWD strategy that is being pursued by the DNR.”

Dave Clausen, former chairman of the Natural Resources Board and a veterinarian who has studied CWD, has also criticized the DNR for being passive on the disease.

He agreed with Meyer that the new research should give the agency pause. He said the potential presence of prions in plants is not only a public health concern but “has big implications for our agricultural economy, not just in this state but all across the country.”

Source: Wisconsin Department of Natural Resources website.

Disease has spread

Soon after the discovery of CWD in Wisconsin, the DNR embarked on an aggressive effort to halt spread of the disease by putting in place additional and longer hunting seasons, requiring hunters to shoot a female deer before taking a buck, and hiring sharpshooters to kill deer.

But the ambitious program grew unpopular with hunters and landowners, and the number of hunters participating in the state’s annual deer hunt declined. Meanwhile, the disease spread.

The DNR reports that prevalence of the disease has increased in all sex and age classes of deer. During the past 11 years, for example, agency data estimates prevalence in adult males has risen from 8 to 10 percent, to more than 20 percent. And in adult females, the prevalence has grown from about 3 or 4 percent to about 9 percent.

Prevalence charts

Wisconsin Department of Natural Resources charts estimating prevalence of chronic wasting disease for male and female deer:


In a disease hot spot in southwestern Wisconsin, CWD prevalence has increased to 27 percent among deer 2 ½ years or older, according to DNR statistics. The growth was called “frightening” by Robert Rolley, a DNR researcher who worked on the study.

And the disease has spread far beyond where it originally showed up. Two years ago, the disease was discovered in a doe in Washburn County in northeastern Wisconsin. Testing has turned up no other infected deer in the area.

Administration scaled back CWD

Gov. Scott Walker promised hunters while campaigning that he would reevaluate the agency’s approach to deer hunting and the disease. After his election, he hired Texas deer expert James Kroll for the job.

Kroll downplayed the potential impact of CWD, both in his report to Walker and in a July white paper on the disease. He did not return phone calls seeking comment on the prion plant study.

In the white paper, Kroll cited studies of the Wisconsin deer herd from 2003 to 2007 showing no increased mortality rates from CWD. He also wrote, “it is my opinion CWD does not pose a threat to human health,” citing studies on the lack of transmission.

He recommended the agency take a “more passive approach” to the illness.

As a result of hunter concerns and Kroll’s report, the DNR has eliminated many of the extra hunting seasons and regulations intended to reduce herd size and slow the spread of the disease. Testing for the disease has also dropped off.

Research unlikely to prompt revision

Tom Hauge, who directs the DNR’s wildlife management program, said the new research is unlikely to cause the agency to reevaluate its CWD program.

“Current management is grounded in the reality of the present conditions,” Hauge said. “There is no science to indicate that human health is at risk to date. And livestock to date have not been impacted. That reality has shaped the socioeconomic response.”

Hauge also said the current political atmosphere has been a factor. He said the special CWD regulations “wore thin on people” and that “manifested itself in a gubernatorial campaign.”

“Until that landscape changes,” Hauge said, “we have to live with the realities we face right now.”

Concerns raised, but questions remain

Tami Ryan, who heads the DNR’s Wildlife Health Section, helped organize The Wildlife Society session at which Johnson will present his findings. She said she invited him because the agency is interested in learning more about the research. She called the initial work “very important research” but said she wants to see more data, especially on whether lab animals can become infected by eating tainted plant material rather than just via injection.

“I’m also interested in the contamination level,” Ryan said. “What is the concentration and frequency of exposure that would result in infection? Is this as great a risk as coming into contact with another infected animal? A level of risk assessment is necessary.”

For the moment, she said, “I don’t hear alarm bells.”

Johnson said he is testing whether animals can become infected by eating CWD-laden plant tissues. He also said future work will address the questions raised by Ryan about the prion concentrations in plants necessary to cause infection.

“We’re just scratching the surface here,” Johnson said.

But Bryan Richards, CWD project leader at the National Wildlife Health Center, said even the findings to date should be taken seriously by state and federal wildlife and public health agencies.

“The potential for exposure is undeniable,” Richards said.

Can humans get CWD?

Clausen said the plant research should be considered in the context of other CWD studies. He said research has shown the molecular barriers that seem to have protected humans from infection may be more porous than some believe.

In 2004, for example, a CDC study published in the scientific journal Emerging Infectious Diseases concluded that the transmission of bovine spongiform encephalopathy, or mad cow disease, to humans indicates that “the species barrier may not completely protect humans from animal protein diseases.”

The article also cited lab studies in which CWD prions were found to infect human prion proteins. Still, the article concluded, “limited investigations have not identified strong evidence for CWD transmission to humans.”

Another study, led by Marcelo Barria from the Mitchell Center for Alzheimer’s Disease and Related Brain Disorders at the University of Texas and published in the March 2011 issue of the Journal of Biological Chemistry, showed that CWD prions in the laboratory can be manipulated over generations to change and become more infectious to humans.

“Our findings lead to a new view that the species barrier should not be seen as a static process but rather a dynamic biological phenomenon that can change over time when prion strains mature and evolve,” the researchers concluded.

Such science, Clausen said, should raise questions about a management approach to CWD that does not stem the spread of the disease and, as a result, increases the risk of human and animal exposure.

“The DNR’s official approach to environmental contamination with CWD prions has been a yawn and a shrug. Whether concerns from consumers, public health officials or agricultural interests will change that is an open question at this time,” Clausen said.

John Stauber, an activist and co-author of the book “Mad Cow USA,” said the new research should be especially sobering in a nation he believes is ignoring a possible dangerous public health threat.

“The implications of prion diseases potentially (spreading) via contaminated agricultural plants is mind-boggling,” Stauber said. “Imagine people, wildlife or livestock eating a cereal or vegetable that could years or decades later cause an incurable, fatal brain disease.

“The best scientists have always warned that with prions, all bets are off. There is no other deadly disease agent as bizarre or invisible. Unfortunately, federal and state food and wildlife agencies have been ignoring the prion threat, downplaying its human health risks, cutting back on research, and pretending this will all go away. It won’t.”

The nonprofit Wisconsin Center for Investigative Journalism ( collaborates with Wisconsin Public Radio, Wisconsin Public Television, other news media and the UW-Madison School of Journalism and Mass Communication. All works created, published, posted or disseminated by the Center do not necessarily reflect the views or opinions of UW-Madison or any of its affiliates.

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Ron Seely joined the Center as a part-time reporter, editor and student mentor in June 2013 after nearly 35 years as an award-winning environmental reporter for the Wisconsin State Journal.

5 replies on “Prions — in plants? New concern for chronic wasting disease”

  1. It certainly appears that CWD is escalating. Reflecting on this growth leads me to reflect on the possible interconnection between the huge increase in the use of RoundUp and other herbicides and pesticides that are applied to GMO plant monocultures such as corn and soybeans.

    These chemicals that owe their lethality to working on the very foundations of life itself, may be playing a role in the increase in the amount of prions found in our environment. Deer feed on stubble and plant residue in harvested fields where herbicidal residuals are likely in great abundance. RoundUp (glyphosate)and related chemicals are also being identified in surface water.

    This is an area that needs prompt and in depth research by independent studies freed from the constraints of monetary infusions from special interest groups.

  2. Excellent, detailed article … but scary. I hope it will get the attention it deserves.

    I woke up this morning from a nightmare about this issue, just from seeing the headline at the top of this website for several days. I had avoided READING the article until now, because I honestly didn’t want to know. (There’s already so much else to worry about that it’s all overwhelming sometimes.) But I finally decided to read the article this morning, figuring I might as well have ACCURATE nightmares if I can’t even prevent the IDEA from eating into my brain.

    So once again, I’ve had to learn about another frightening issue and another stunningly-stupid non-response from our society and government.

    How can so many people be so appallingly shortsighted and careless about the future? Why are decision-makers so willing to allow such an enormous risk to spread, simply because they lack absolute, scientific certainty about every single aspect of this threat?

    Humanity is DOOMED if we allow ourselves to be paralyzed like this every time a significant new risk is discovered. At some point, we’ll push our luck too far.

    What ever happened to the old wisdom, “Better safe, than sorry?”

    And WHY are Wisconsin leaders listening to a DEER MANAGER from Texas when he says, “It is my opinion CWD does not pose a threat to human health.”

    This man is NOT a doctor, and definitely not a medical expert concerning CWD prion risks to human health. He has no basis for making such an absolute claim, yet this non-expert is allowed to veto the carefully developed recommendations of experienced, credentialed state and national specialists who better-understand the science and TRUE risks behind this issue.

    Our future seems increasingly controlled by willfully ignorant people who rule us all based on short-term costs, expediency, wishful thinking, and gut-level OPINIONS, not science.

    Our technologies may be advancing, but the combined WISDOM of our society seems to be degenerating.

  3. Seven key points raised by this article deserve emphasis … and SHOULD spur immediate, aggressive government actions to stop the CWD epidemic:

    1. CWD prions in the laboratory can be manipulated over generations to change and become more infectious to humans.

    If this can happen in a lab, it could happen in nature. Other forms of prions have already transformed into well-known HUMAN diseases, so why do Republicans believe such a mutation is impossible, or even unlikely, for CWD? In the 1990s, a similar prion disease in England, which previously affected only livestock, suddenly mutated and jumped the “species barrier” to infect and kill 184+ people.

    2. Research has shown the molecular barriers that seem to have protected humans from infection may be more porous than some believe.

    Human bodies are not all that different from those of deer. We humans think we’re “special” and invulnerable, when really, we’re not.

    3. Lab studies have found that CWD prions can infect human prion proteins.

    CWD prions just need to mutate enough to REACH human brain proteins. Once in the brain, CWD could easily be as bad as any other fatal prion disease.

    4. CWD prions can be taken up by plants such as alfalfa, corn and tomatoes.

    If CWD moves so freely in the environment and spreads all across the continent, it could become impossible to find a human food source in North American that is reliably NOT infected with CWD.

    (Other regions of the world would be smart to quarantine North American and bar imports of our products long before our infection rates get that bad.)

    5. Stems and leaves from tainted plants were infectious when injected into laboratory mice.

    Humans and animals suffering from even minor fresh cuts and scrapes might be infected just through contact with CWD infected plant material (dead or alive). Will kids have to wear rubber body suits before they play in a neighbor’s field?

    6. CWC can be transmitted animal-to-animal and via soil.

    And human-to-human when CWD successfully mutates to infect humans?

    7. CWD prions can linger in and be amplified and transmitted by soil.

    Will contaminated DUST become infectious when CWD crosses the species barrier? Will gardeners become infected with CWD when prion-contaminated soil gets into a fresh scratch from a rose bush? The possibilities are mind-boggling.

  4. I fully agree! Only until the powers to be have lost a loved one! From CWD don’t expect to much response from the Gov officials! Many Ag & Wildlife Agencies have been told not to say anything negative about Deer Farmers!

    There’s plenty of Cronies that are paid Prostitutes, with Phd”s that will say anything to defend this practice! It’s a real Joke!

    Don’t want to alarm you but Deer Farmers never Report any Deer that escape their facility’s! Michigan alone found over 500 Deer unaccounted for! Can you image how many Deer have escaped Nationwide from behind the fence!

    However, nobody’s going to silence me about what I know! I’m starting a campaign to close the borders in every state! This is going to take some Funding! Hunters and Citizen Against Deer Farming!

    Every State Must Close Their Borders! To Protect It’s Wildlife & Citizens & The Pubic Trust & The North American Conservation Model!



  5. I’ve seen hundreds of wild deer and elk eating so-called CANOLA in farmer’s fields – there is no mention of that GE crop in this story. Why?

    There never was a CANOLA plant before Monsanto’s GMO/GE onslaught on the our agriculture (food).

    “CANOLA” is a poorly thought up acronym for “CANADA OIL”. The oil came from the RAPE PLANT and was originally used as an industrial lubricant. Mustard Gas also came from the rape plant, and was used extensively as a chemical weapon during WWI…The Great War.

    “Particle bombardment (GMO/GE) can cause unpredictable changes and
    mutations in the DNA (GMO plants and other ‘food’ products) which might
    result in new types of proteins…prion.

    Proteins can have allergenic or toxic properties – no one at Monsanto did safety assessments on them.”

    (brackets mine)

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