Pittsburgh, Pa. — Recent research has shown that plant roots can absorb prions that cause chronic wasting disease from soil, although it is unclear whether animals eating those plants can be infected by CWD.
Christopher Johnson, of the National Wildlife Health Center in Madison, Wis., has discovered that plants take up prions – infectious, deformed proteins – from contaminated soils and store them in stems and leaves.
In turn, when Johnson injected these materials into laboratory mice, they showed evidence of the disease. Johnson is awaiting test results to determine if other lab mice caught the disease after eating infected plants.
Johnson wrote: “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.”
Johnson was to present his findings Oct. 7 in Milwaukee at the annual meeting of The Wildlife Society. However, because he’s employed by the U.S. Geological Survey, his talk was canceled by the government’s budget impasse, and he was not able to share more insights for now.
Because prions aren’t living organisms, they remain infectious indefinitely, whether they’re in soil or living matter. And although CWD prions were once thought to be confined to the brain, spleen, tonsils, lymph nodes, and spinal cord of deer and elk, they’ve since been found at lower levels in their eyes, heart, blood, urine, saliva, and muscles.
So far, science has found no evidence that CWD can infect humans who eat contaminated venison, but the World Health Organization and the Pennsylvania Game Commission advise people not to eat CWD-positive animals.
The state of Wyoming adds this warning: “Until more is known about the human health risk, individuals may want to consider the theoretical possibility that a yet-to-be-determined human health risk may exist before consuming CWD-infected animals.”
Johnson’s findings raise concerns beyond the deer-hunting world. One unknown is whether plants alter CWD prions in ways that make them increasingly infectious. Laboratory tests show that prions injected into mice can change enough that even though the first mouse doesn’t die, its tissues kill mice in subsequent injections.
We also don’t know how much prion concentrations vary by individual plants and plant species, or how much prion uptake through roots varies by soil-contamination levels.
And depending on whether Johnson’s lab mice contract CWD by eating prion-tainted plants, we need to learn whether it takes a spoonful – or a barnful – of the stuff.
So far, Johnson has tested corn, alfalfa, tomatoes and thale cress – a small, flowering plant used in plant-science research.
Consider the stakes: If state and federal agencies think it prudent to tell hunters to destroy prion-contaminated venison, will they soon warn everyone about prion-tainted plants?
For that matter, will they stop farmers from buying, selling, and transporting hay bales out of CWD zones?
And what about backyard gardens, morel mushrooms, wild raspberries, and feed-grains growing in the CWD zones? Should we assume they’re prion-free?
And if Great Britain and other countries won’t import U.S. animal feeds containing CWD-exposed meat by-products, will they next ban plant-based feeds?
Granted, it’s silly to suggest raiding farmers’ markets and roadside stands that sell foods grown in CWD areas. We simply don’t know enough to risk a CWD panic.
But this much is certain: As we’ve slowly assembled the CWD puzzle piece by piece, the picture has only grown uglier.