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A new publication, Carlson, et al. (2023), demonstrated the ability of several crop species, including alfalfa and barley, commonly consumed by cervids and livestock, to uptake prions via their roots and translocate them to above-ground tissue.

Why this matters: Despite decades of research, precise transmission pathways for CWD remain unclear. Previous research identified that plants can uptake prions via their roots and deposit them in stems and leaves but did not address whether these plants could transmit disease. In the current study, Carlson, et al. (2023) demonstrated that common agricultural crops, grown in prion-spiked substrates, could transmit prion disease to laboratory animals. While the authors encourage caution in interpreting these results, it is the first conclusive research of its type.

Plants growing in lab flasks under lights.
Plants were grown in prion-spiked growth media at the National Wildlife Health Center to investigate the role of prion contaminated plants in CWD transmission dynamics.

Prions, misfolded isoforms of a normal mammalian cellular protein, cause progressive, fatal neurodenerative diseases including chronic wasting disease (CWD) in cervids, scrapie in sheep and goats, bovine spongiform encephalopathy (often referred to as “mad cow disease”) in cattle, and Creutzfeldt-Jakob disease in humans. Prions exhibit extraordinary resistance to common treatments used to denature other infectious agents, such as ultraviolet and ionizing radiation, exposure to chemical disinfectants, and heat treatments. With CWD and scrapie, infectious prions may be transmitted to healthy, naïve, susceptible animal hosts via environmental routes and the ability of plants to accumulate and subsequently transmit disease has been hypothesized.

Pritzkow, et al. (2015) demonstrated that prions can bind to roots and leaves of plants that were surface contaminated with prion-containing solutions (e.g., brain homogenate, urine, feces) and that these prion-contaminated plants could cause disease when orally consumed by experimental laboratory animals. They also demonstrated uptake and deposition of prions in stems and leaves of plants grown in prion-spiked soils, but did not demonstrate whether consumption of these plants could cause infection.

Scientists from the USGS National Wildlife Health Center, University of Wisconsin-Madison, University of Texas Health Science Center, University of Pennsylvania, Universidad Bernardo O’Higgins, and Johns Hopkins University built upon Pritzkow et al. by examining not only whether plants could uptake and deposit prions in aerial tissues, but also whether these plants could serve as vectors for prion diseases via oral consumption. Carlson, et al. (2023) demonstrated the ability of several crop species, including alfalfa and barley, commonly consumed by cervids and livestock, to uptake prions via their roots and translocate them to above-ground tissues from various growth media, including soils, spiked with prions. And while plants cannot amplify prion burden like mammals, they were shown to accumulate prions in above-ground tissues in levels sufficient to transmit disease after oral ingestion by mice. The results of this study corroborate and extend the work of Pritzkow et al. and highlight mechanisms by which plants may serve as vectors for prion transmission in the environment. While this study has potential implications for wildlife conservation, agriculture, and public health, the authors have highlighted that this work was conducted in a laboratory environment (not in a field setting) with artificially-contaminated soils, did not use CWD or scrapie prions, did not use a ruminant model, and that additional investigations will be required to evaluate the degree to which prion-contaminated plants contribute to CWD and scrapie transmission dynamics.

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