TABLE 1.

Infectivity in whole blood of VRQ/VRQ sheep orally challenged with PG127 scrapie agent as determined by intracerebral inoculation in tg338 mice^a

Donor	Total inoculated volume (whole blood; μl)	Positive mice (no. positive/total no.)	ID per ml of whole blood (95% CI)
D1	340	0/17	<8.81b
D2	340	2/17	6.3 (1–19.4)
D3	360	1/18	2.9 (0.2–12.6)
D4	360	1/18	2.9 (0.2–12.6)

^aBlood was collected from the four VRQ/VRQ donor sheep that had been orally challenged with PG127 scrapie (D1, D2, D3, and D4) 180 days postinoculation. Donor sheep developed clinical scrapie 2 to 5 weeks following blood collection and were euthanized at 207, 219, 217, and 196 dpi, respectively. Whole blood from donor sheep was inoculated intracerebrally (i.c.) into 18 tg338 mice (20 μl per mouse). Two mice (inoculated with blood from donors D1 and D2) died within the first few days following i.c. inoculation. Mice were euthanized when they showed clinical signs of prion infection or after 250 dpi. Mice were considered prion infected when abnormal PrP deposition was detected in the brain. Infectious prion titers were estimated using the limiting dilution titration method (application of Poisson's model) as described by Brown et al. (28). Infectious titers are given as the most likely values.

^bWhen no transmission was observed, the detection limit of the bioassay is indicated (upper boundary of the 95% CI).