PRNP and scrapie: (3) While the molecular structure of TSE agents remains unknown, virus-like dense particles of 20–25 nm within infected CJD and scrapie cells (Manuelidis et al., 2007) are also concentrated in highly infectious preparations with reduced or no PrP/PrP-res (Manuelidis, 2007; Kipkorir et al., 2014).