Table 7.

Intracerebral inoculation of tg338 mice with platelets, washed or unwashed WBC prepared from VRQ/VRQ sheep orally inoculated with PG127 scrapie^a

Sheep	Result by sample
	Platelets		WBC (unwashed)		WBC (5 washes)		WBC (10 washes)
	No. of mice positive for abnormal PrP	Length of incubation (days)	No. of mice positive for abnormal PrP	Length of incubation (days)	No. of mice positive for abnormal PrP	Length of incubation (days)	No. of mice positive for abnormal PrP	Length of incubation (days)
D7	6/6	95 ± 10	6/6	84 ± 3	6/6	87 ± 4	6/6	85 ± 3
D8	6/6	97 ± 4	6/6	87 ± 4	6/6	92 ± 7	6/6	96 ± 3
D9	3/5	108 ± 6	5/5	84 ± 3	5/5	86 ± 4	5/5	85 ± 3
D10	5/5	98 ± 8	5/5	93 ± 9	5/5	95 ± 3	5/5	106 ± 6
D11	4/5	113 ± 12	5/5	88 ± 2	5/5	97 ± 3	5/5	93 ± 3

^aFive susceptible VRQ/VRQ sheep (identified as D7, D8, D9, D10, and D11) were orally challenged with 2 g of brain homogenate (10^6.6 ID₅₀/g IC in tg338 mice) between 6 and 10 months of age. These animals died at 228, 248, 256, 242, and 244 dpi, respectively. Classical scrapie occurrence was confirmed by histopathology (vacuolar changes in the central nervous system) and the detection of abnormal PrP deposits in the central nervous system and lymphoid tissues. Whole-blood samples (15 ml) were collected at 220 dpi, and platelets (derived from platelet-rich plasma) and WBC were prepared. WBC was washed 5 or 10 times in PBS-5 mM EDTA. WBC (washed and unwashed) corresponding to 5 ml of starting blood and platelets corresponding to a starting volume of 15 ml were resuspended into 120 μl of 5% glucose before homogenization. Each homogenate was inoculated (20 μl) intracerebrally into tg338 mouse groups (n = 6). Mice then were observed until the occurrence of clinical signs or killed after 200 days postinoculation. Mice were considered positive when abnormal PrP deposition was detected in the brain. Incubation periods are presented as means ± SD.