FIG 2.

End-point titrations to determine the prion 50% seeding dose (SD₅₀) present in the CWD-infected brain stock used for the feeding experiments and in the resulting prion-positive fecal samples. (A and B) CWD-infected brain was diluted directly in RT-QuIC buffer (A) or used to spike a 10% mountain lion fecal homogenate prior to dilution in RT-QuIC buffer (B). Positive fecal samples from experiments 1 and 2 were also diluted to determine prion SD₅₀ (C and D). Each curve shown is the average fluorescence of 4 wells tested per dilution. As samples become more dilute, the time to reach a positive reaction increases. The dilutions are labeled to the right of each curve and are shown with different symbols and colors, followed by a fraction indicating the number of positive wells of the total tested.