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.”
This project was supported by The Joyce Foundation. The nonprofit Wisconsin Center for Investigative Journalism (www.WisconsinWatch.org) collaborates with Wisconsin Public Radio, Wisconsin Public Television, other news media and the UW-Madison School of Journalism and Mass Communication.
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