Prion infectivity in variant Creutzfeldt-Jakob disease rectum.

BACKGROUND: Disease-related prion protein (PrP(Sc)) is readily detectable in lymphoreticular tissues in variant Creutzfeldt-Jakob disease (vCJD), but not in other forms of human prion disease. This distinctive pathogenesis, with the unknown population prevalence of asymptomatic vCJD infection, has led to significant concerns that secondary transmission of vCJD prions will occur through a wide range of surgical procedures. To date PrP(Sc):prion infectivity ratios have not been determined in vCJD, and it is unknown whether vCJD prions are similar to experimental rodent prions, where PrP(Sc) concentration typically reflects infectious prion titre. AIM: To investigate prion infectivity in vCJD tissue containing barely detectable levels of PrP(Sc). METHODS: Transgenic mice expressing only human PrP (Tg(HuPrP129M(+/+)Prnp(o/o))-35 and Tg(HuPrP129M(+/+)Prnp(o/o))-45 mice) were inoculated with brain or rectal tissue from a previously characterised patient with vCJD. These tissues contain the maximum and minimum levels of detectable PrP(Sc) that have been observed in vCJD. RESULTS: Efficient transmission of prion infection was observed in transgenic mice inoculated with vCJD rectal tissue containing PrP(Sc) at a concentration of 10(4.7)-fold lower than that in vCJD brain. CONCLUSIONS: These data confirm the potential risks for secondary transmission of vCJD prions via gastrointestinal procedures and support the use of PrP(Sc) as a quantitative marker of prion infectivity in vCJD tissues.

Tissue distribution of protease resistant prion protein in variant Creutzfeldt-Jakob disease using a highly sensitive immunoblotting assay.

BACKGROUND: Variant Creutzfeldt-Jakob disease (vCJD) has a pathogenesis distinct from other forms of human prion disease: disease-related prion protein (PrP(Sc)) is readily detectable in lymphoreticular tissues. Quantitation of risk of secondary transmission, and targeting of risk reduction strategies, is limited by lack of knowledge about relative prion titres in these and other peripheral tissues, the unknown prevalence of preclinical vCJD, and a transmission barrier which limits the sensitivity of bioassay. We aimed to improve immunoblotting methods for high sensitivity detection of PrP(Sc) to investigate the distribution of PrP(Sc) in a range of vCJD tissues. METHODS: We obtained tissues at necropsy from four patients with neuropathologically confirmed vCJD and from individuals without neurological disease. Tissues were analysed by sodium phosphotungstic acid precipitation of PrP(Sc) and western blotting using high sensitivity enhanced chemiluminescence. FINDINGS: We could reliably detect PrP(Sc) in the equivalent of 50 nL 10% vCJD brain homogenate, with a maximum limit of detection equivalent to 5 nl. PrP(Sc) could be detected in tissue homogenates when present at concentrations 10(4)-10(5) fold lower than those reported in brain. Tonsil, spleen, and lymph node were uniformly positive for PrP(Sc) at concentrations in the range of 0.1-15% of those found in brain: the highest concentrations were consistently seen in tonsil. PrP(Sc) was readily detected in the retina and proximal optic nerve of vCJD eye at levels of 2.5 and 25%, respectively of those found in brain. Other peripheral tissues studied were negative for PrP(Sc) with the exception of low concentrations in rectum, adrenal gland, and thymus from a single patient with vCJD. vCJD appendix and blood (Buffy coat fraction) were negative for PrP(Sc) at this level of assay sensitivity. INTERPRETATION: We have developed a highly sensitive immunoblot method for detection of PrP(Sc) in vCJD tissues that can be used to provide an upper limit on PrP(Sc) concentrations in peripheral tissues, including blood, to inform risk assessment models. Rectal and other gastrointestinal tissues should be further investigated to assess risk of iatrogenic transmission via biopsy instruments. Ophthalmic surgical instruments used in procedures involving optic nerve and the posterior segment of the eye, in particular the retina, might represent a potential risk for iatrogenic transmission of vCJD. Tonsil is the tissue of choice for diagnostic biopsy and for population screening of surgical tissues to assess prevalence of preclinical vCJD infection within the UK and other populations.

Species-barrier-independent prion replication in apparently resistant species.

Transmission of prions between mammalian species is thought to be limited by a "species barrier," which depends on differences in the primary structure of prion proteins in the infecting inoculum and the host. Here we demonstrate that a strain of hamster prions thought to be nonpathogenic for conventional mice leads to prion replication to high levels in such mice but without causing clinical disease. Prions pathogenic in both mice and hamsters are produced. These results demonstrate the existence of subclinical forms of prion infection with important public health implications, both with respect to iatrogenic transmission from apparently healthy humans and dietary exposure to cattle and other species exposed to bovine spongiform encephalopathy prions. Current definitions of the species barrier, which have been based on clinical end-points, need to be fundamentally reassessed.