Failure to detect abnormal prion protein and scrapie-associated fibrils 6 wk after intracerebral inoculation of genetically susceptible sheep with scrapie agent
Hamir, A.N.; Miller, J.M.; Stack, M.J.; Chaplin, M.J.
Canadian Journal of Veterinary Research 66(4): 289-294
ISSN/ISBN: 0830-9000 PMID: 12418787 Accession: 010654335
Detection of the scrapie-associated protease-resistant prion protein (PrPres) in sheep brains in the early phase after intracerebral inoculation of the scrapie agent has not been documented. Fourteen 4-mo-old, genetically susceptible lambs (QQ homozygous at codon 171 of the PrP gene) were obtained for this study. Twelve lambs were inoculated intracerebrally with a brain suspension from sheep naturally affected with scrapie, and 2 served as uninoculated controls. Two inoculated animals were euthanized at each of 6 times postinoculation (1 h to 6 wk), and their brains were collected for histopathological study, for detection of PrPres by the Western blot technique and an immunohistochemical (IHC) method, and for the detection of scrapie-associated fibrils (SAF) by negatively stained electron microscopy (EM). Microscopic lesions associated with introduction of the inoculum were seen in the brains of inoculated animals at all 6 times. However, both the Western blot and IHC techniques did not detect PrPres after the initial 3 d postinoculation, nor did EM detect SAF in any of the samples. From these findings, it is presumed that until host amplification has occurred, the concentration of PrPres in inoculum is insufficient for detection by currently available techniques.