The levels of infectious prions in animals infected with chronic wasting disease (CWD) in cervids, as with variant Creutzfeldt-Jakob-disease (vCJD) in human, are often beyond the limits of detection using conventional assays. In addition, the mechanisms of pathogenesis and transmission of prion diseases are not clearly defined. Development of sensitive antemortem assays for CWD and an understanding of transmission are critical for the eventual control of prion diseases of both man and animals. We propose to study CWD of cervids as a model for vCJD/prion transmission. CWD PrPres has been shown to be present and transmissible in various excreta, including saliva, blood, urine and feces of infected deer, though other biological samples may also serve as routes of transmission between cervids. In addition, detectable levels and the exact source of PrPres in these excreta have yet to be demonstrated. We propose three aims which explore the pathogenesis and transmission of prion diseases: (1) in Aim 1, we will evaluate peripheral tissues for early accumulation of CWD prions using a sensitive amplification assay, sPMCA. These findings will be compared with those achieved using more traditional assays such as immunohistochemistry. (2) In Aim 2, we will seek to determine the kinetics of prion shedding in saliva and urine through samples collected at multiple time points from infected cervids using bioassay and PMCA. Findings will be compared to results of early detection in peripheral tissues (Aim 1) as well as the sensitivity and specificity of current antemortem assays. (3) In Aim 3, we will investigate the tissue and cellular origins infectious prions in biological samples using immunocyto- and histochemistry, bioassay, and PMCA. The results of these studies will contribute greatly to the understanding of pathogenesis and transmission potential of CWD, BSE, and vCJD.
A critical limitation of prion disease intervention strategies is the lack of knowledge regarding mechanisms and dynamics of transmission and a suitable antemortem assay. Additionally, little is known about the biological nature of prions in excreta (e.g. urine and saliva), and identifying the tissues and cell types involved in prion transmission is relevant to both the pathogenesis and diagnosis of TSE's.
