Transmission and detection of prions in feces

Infectious prions in pre-clinical deer and transmission of chronic wasting disease solely by environmental exposure

Key to understanding the epidemiology and pathogenesis of prion diseases, including chronic wasting disease (CWD) of cervids, is determining the mode of transmission from one individual to another. We have previously reported that saliva and blood from CWD-infected deer contain sufficient infectious prions to transmit disease upon passage into naïve deer. Here we again use bioassays in deer to show that blood and saliva of pre-symptomatic deer contain infectious prions capable of infecting naïve deer and that naïve deer exposed only to environmental fomites from the suites of CWD-infected deer acquired CWD infection after a period of 15 months post initial exposure. These results help to further explain the basis for the facile transmission of CWD, highlight the complexities associated with CWD transmission among cervids in their natural environment, emphasize the potential utility of blood-based testing to detect pre-clinical CWD infection, and could augur similar transmission dynamics in other prion infections.

Infectious prions in pre-clinical deer and transmission of chronic wasting disease solely by environmental exposure

Key to understanding the epidemiology and pathogenesis of prion diseases, including chronic wasting disease (CWD) of cervids, is determining the mode of transmission from one individual to another. We have previously reported that saliva and blood from CWD-infected deer contain sufficient infectious prions to transmit disease upon passage into naïve deer. Here we again use bioassays in deer to show that blood and saliva of pre-symptomatic deer contain infectious prions capable of infecting naïve deer and that naïve deer exposed only to environmental fomites from the suites of CWD-infected deer acquired CWD infection after a period of 15 months post initial exposure. These results help to further explain the basis for the facile transmission of CWD, highlight the complexities associated with CWD transmission among cervids in their natural environment, emphasize the potential utility of blood-based testing to detect pre-clinical CWD infection, and could augur similar transmission dynamics in other prion infections.

Prions are secreted in milk from clinically normal scrapie-exposed sheep

The potential spread of prion infectivity in secreta is a crucial concern for prion disease transmission. Here, serial protein misfolding cyclic amplification (sPMCA) allowed the detection of prions in milk from clinically affected animals as well as scrapie-exposed sheep at least 20 months before clinical onset of disease, irrespective of the immunohistochemical detection of protease-resistant PrP(Sc) within lymphoreticular and central nervous system tissues. These data indicate the secretion of prions within milk during the early stages of disease progression and a role for milk in prion transmission. Furthermore, the application of sPMCA to milk samples offers a noninvasive methodology to detect scrapie during preclinical/subclinical disease.

Detection of CWD prions in urine and saliva of deer by transgenic mouse bioassay

Chronic wasting disease (CWD) is a prion disease affecting captive and free-ranging cervids (e.g. deer, elk, and moose). The mechanisms of CWD transmission are poorly understood, though bodily fluids are thought to play an important role. Here we report the presence of infectious prions in the urine and saliva of deer with chronic wasting disease (CWD). Prion infectivity was detected by bioassay of concentrated, dialyzed urine and saliva in transgenic mice expressing the cervid PrP gene (Tg[CerPrP] mice). In addition, PrP^CWD was detected in pooled and concentrated urine by protein misfolding cyclic amplification (PMCA). The concentration of abnormal prion protein in bodily fluids was very low, as indicated by: undetectable PrP^CWD levels by traditional assays (western blot, ELISA) and prolonged incubation periods and incomplete TSE attack rates in inoculated Tg(CerPrP) mice (373^±3days in 2 of 9 urine-inoculated mice and 342^±109 days in 8 of 9 saliva-inoculated mice). These findings help extend our understanding of CWD prion shedding and transmission and portend the detection of infectious prions in body fluids in other prion infections.

Trans-species amplification of PrP(CWD) and correlation with rigid loop 170N

Chronic wasting disease (CWD) is an efficiently transmitted spongiform encephalopathy of cervids. Whether CWD could represent a threat to non-cervid species remains speculative. Here we show that brain homogenates from several CWD-susceptible non-cervid species, such as ferrets and hamsters, support amplification of PrP(CWD) by sPMCA, whereas brain homogenates from CWD-resistant species, such as laboratory mice and transgenic mice expressing human PrP(C) [Tg(HuPrP) mice], do not. We also investigated whether several North American species that share the environment with cervids would support amplification of PrP(CWD) by sPMCA. Three native rodent species, including voles and field mice, supported PrP(CWD) amplification, whereas other species (e.g. prairie dog, coyote) did not. Analysis of PrP sequences suggests that an ability to support amplification of PrP(CWD) in trans-species sPMCA is correlated with the presence of asparagine at position 170 of the substrate species PrP. Serial PMCA may offer insights into species barriers to transmission of CWD.

Pathogenic prion protein is degraded by a manganese oxide mineral found in soils

Prions, the aetiological agents of transmissible spongiform encephalopathies, exhibit extreme resistance to degradation. Soil can retain prion infectivity in the environment for years. Reactive soil components may, however, contribute to the inactivation of prions in soil. Members of the birnessite family of manganese oxides (MnO(2)) rank among the strongest natural oxidants in soils. Here, we report the abiotic degradation of pathogenic prion protein (PrP(TSE)) by a synthetic analogue of naturally occurring birnessite minerals. Aqueous MnO(2) suspensions degraded the PrP(TSE) as evidenced by decreased immunoreactivity and diminished ability to seed protein misfolding cyclic amplification reactions. Birnessite-mediated PrP(TSE) degradation increased as a solution's pH decreased, consistent with the pH-dependence of the redox potential of MnO(2). Exposure to 5.6 mg MnO(2) ml(-1) (PrP(TSE) : MnO(2)=1 : 110) decreased PrP(TSE) levels by > or = 4 orders of magnitude. Manganese oxides may contribute to prion degradation in soil environments rich in these minerals.

Faecal shedding, alimentary clearance and intestinal spread of prions in hamsters fed with scrapie

Shedding of prions via faeces may be involved in the transmission of contagious prion diseases. Here, we fed hamsters 10mg of 263K scrapie brain homogenate and examined the faecal excretion of disease-associated prion protein (PrP(TSE)) during the course of infection. The intestinal fate of ingested PrP(TSE) was further investigated by monitoring the deposition of the protein in components of the gut wall using immunohistochemistry and paraffin-embedded tissue (PET) blotting. Western blotting of faecal extracts showed shedding of PrP(TSE) in the excrement at 24-72 h post infection (hpi), but not at 0-24 hpi or at later preclinical or clinical time points. About 5% of the ingested PrP(TSE) were excreted via the faeces. However, the bulk of PrP(TSE) was cleared from the alimentary canal, most probably by degradation, while an indiscernible proportion of the inoculum triggered intestinal infection. Components of the gut-associated lymphoid tissue (GALT) and the enteric nervous system (ENS) showed progressing accumulation of PrP(TSE) from 30 days post infection (dpi) and 60 dpi, respectively. At the clinical stage of disease, substantial deposits of PrP(TSE) were found in the GALT in close vicinity to the intestinal lumen. Despite an apparent possibility of shedding from Peyer's patches that may involve the follicle-associated epithelium (FAE), only small amounts of PrP(TSE) were detected in faeces from clinically infected animals by serial protein misfolding cyclic amplification (sPMCA). Although excrement may thus provide a vehicle for the release of endogenously formed PrP(TSE), intestinal clearance mechanisms seem to partially counteract such a mode of prion dissemination.

Prions in the environment: occurrence, fate and mitigation

Scrapie and CWD are horizontally transmissible, and the environment likely serves as a stable reservoir of infectious prions, facilitating a sustained incidence of CWD in free-ranging cervid populations and complicating efforts to eliminate disease in captive herds. Prions will enter the environment through mortalities and/or shedding from live hosts. Unfortunately, a sensitive detection method to identify prion contamination in environmental samples has not yet been developed. An environmentally-relevant prion model must be used in experimental studies. Changes in PrP(Sc) structure upon environmental exposure may be as significant as changes in PrP(Sc) quantity, since the structure can directly affect infectivity and disease pathology. Prions strongly bind to soil and remain infectious. Conformational changes upon adsorption, competitive sorption and potential for desorption and transport all warrant further investigation. Mitigation of contaminated carcasses or soil might be accomplished with enzyme treatments or composting in lieu of incineration.