Conversion efficiency ratio (CER) assay using laboratory mouse substrate. (A) Mouse CER assay substrate prepared at either pH 7.4 or 3.5 was incubated with RML mouse-adapted scrapie, domestic sheep classical scrapie, white-tailed deer (WTD) chronic wasting disease agent (CWD) or 263K strain of hamster-adapted scrapie. Control samples (labeled “none”) contained only an equal amount of infectious agent and no mouse substrate. Samples were analyzed for the presence of proteinase K-resistant prion protein by immunoblot with monoclonal antibody SAF 83. Raw densitometric values for each sample are displayed below each lane. (B) Bar graph indicating the average ratios (+/− standard deviation) between pH 7.4 and 3.5 mouse substrates for each infectious agent based on at least three independent assay runs. Lower-case letters refer to statistically homogeneous subsets (analysis of variance with Tukey-Kramer minimum significance differences method; p < 0.05).