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Abstract
The persistence of infectious biomolecules in soil constitutes a substantial challenge. This holds particularly true with respect to prions, the causative agents of transmissible spongiform encephalopathies (TSEs) such as scrapie, bovine spongiform encephalopathy (BSE), or chronic wasting disease (CWD). Various studies have indicated that prions are able to persist in soil for years without losing their pathogenic activity. Dissemination of prions into the environment can occur from several sources, e.g., infectious placenta or amniotic fluid of sheep. Furthermore, environmental contamination by saliva, excrements or non-sterilized agricultural organic fertilizer is conceivable. Natural transmission of scrapie in the field seems to occur via the alimentary tract in the majority of cases, and scrapie-free sheep flocks can become infected on pastures where outbreaks of scrapie had been observed before. These findings point to a sustained contagion in the environment, and notably the soil. By using outdoor lysimeters, we simulated a contamination of standard soil with hamster-adapted 263K scrapie prions, and analyzed the presence and biological activity of the soil-associated PrPSc and infectivity by Western blotting and hamster bioassay, respectively. Our results showed that 263K scrapie agent can persist in soil at least over 29 months. Strikingly, not only the contaminated soil itself retained high levels of infectivity, as evidenced by oral administration to Syrian hamsters, but also feeding of aqueous soil extracts was able to induce disease in the reporter animals. We could also demonstrate that PrPSc in soil, extracted after 21 months, provides a catalytically active seed in the protein misfolding cyclic amplification (PMCA) reaction. PMCA opens therefore a perspective for considerably improving the detectability of prions in soil samples from the field.
Highlights
Transmissible spongiform encephalopathies (TSEs) comprise a group of fatal neurodegenerative diseases such as bovine spongiform encephalopathy (BSE) in cows [1], chronic wasting disease (CWD) in deer (Odocoileus spp.) and elk (Cervus elaphus nelsoni) [2,3,4], scrapie in sheep and goats [5,6,7] and Creutzfeldt-Jakob disease (CJD) in humans [1]
The regular occurrence of scrapie in affected areas [7] and the spread of CWD in North America and Korea [9,10] among mule deer, white-tailed deer and elk indicates that a contagion in the environment is responsible for the occurrence of these TSEs [4,11,12,13,14], and even raises the possibility of a crossspecies transmission under natural conditions
A few studies have addressed the question of a persistence of prions in soil so far [24,25,26,47], and the results from these studies are in principle in accordance with our observations
Summary
Transmissible spongiform encephalopathies (TSEs) comprise a group of fatal neurodegenerative diseases such as bovine spongiform encephalopathy (BSE) in cows [1], chronic wasting disease (CWD) in deer (Odocoileus spp.) and elk (Cervus elaphus nelsoni) [2,3,4], scrapie in sheep and goats [5,6,7] and Creutzfeldt-Jakob disease (CJD) in humans [1]. The regular occurrence of scrapie in affected areas [7] and the spread of CWD in North America and Korea [9,10] among mule deer, white-tailed deer and elk indicates that a contagion in the environment is responsible for the occurrence of these TSEs [4,11,12,13,14], and even raises the possibility of a crossspecies transmission under natural conditions. Soilassociated TSE agents in the environment represent a potential hazard This holds true not least since prion infectivity exhibits an unusually pronounced resistance against both physical and Academic Editor: Joseph El Khoury, Massachusetts General Hospital & Harvard Medical School, United States of America
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