Bewertung des Vorkommens und der Auswirkung von infektiösen Biomolekülen in Böden unter besonderer Berücksichtigung ihrer Persistenz: Förderkennzeichen (UFOPLAN) 202 73 265 / 201 73 241

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 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. 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. Due to these observations a research project has been conducted at the Fraunhofer IME, Schmallenberg, Germany, for analyzing the persistence of prions in soil more detailed. 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 evidence 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