THE FATE OF INFECTIOUS PRION PROTEINS IN WASTEWATER TREATMENT SYSTEMS

The fate of prion proteins in wastewater treatment systems was investigated. Transmissible spongiform encephalopathies (TSEs), or prion diseases, are fatal neurodegenerative diseases afflicting a variety of mammalian species and include bovine spongiform encephalopathy (BSE or “mad cow” disease), chronic wasting disease (CWD) of deer and elk, sheep scrapie and Creutzfeldt-Jakob disease in humans. The putative infectious agent in these diseases, designated PrPSc, is a misfolded isoform of the normal cellular prion protein. Several reports of healthy animals contracting TSEs when kept on land previously occupied by diseased animals provide indirect evidence of the persistence of prions in the environment (Andreoletti et al., 2000; Miller et al., 2004). Taken together, these data suggest that PrPSc may survive for long periods of time in environmental matrices.PrPSc could potentially enter wastewater treatment systems through disposal of prion-contaminated waste (e.g., sewage from slaughterhouses, landfill leachate, waste material from game dressing). Furthermore, interest exists in employing anaerobic digestion for the disposal of potentially TSE-infected animal material. The degree to which conventional waste treatment processes inactivate PrPSc is unknown. Treated liquid effluent and biosolids are often applied to agricultural land. This could provide a route of introduction of the infectious agent into the environment. Although almost nothing is known about the behavior of PrPSc in engineered systems, the documented recalcitrance of the protein to decontamination measures and a variety of environmental conditions leads us to hypothesize that significant reduction in PrPSc infectivity will not be achieved by most conventional biological waste treatment processes. A better understanding of PrPSc fate in waste treatment systems is needed to assess the risks posed by disposal of TSE-contaminated materials.