Evaluation of the infectivity present in platelets prepared from scrapie infected sheep by two different methods: PMCA and inoculation into tg338 mice (bioassay).

Five susceptible VRQ/VRQ sheep were orally challenged with 2 g of brain homogenate (106.6 ID50/g IC in tg338 mice) between 6 and 10 months of age. The five VRQ/VRQ sheep respectively died at 198, 193, 198, 194 and 191days post inoculation (dpi). Classical scrapie was confirmed by histopathology (vacuolar change in central nervous system) and detection of abnormal PrP deposit in central nervous system and lymphoid tissues. At different time points, whole blood was collected from each donor and aliquots of platelets corresponding to 15 mL of plasma were prepared. Platelet homogenates (in 200μL) were inoculated in groups of six tg338 mice. Mice were monitored up to occurrence of TSE compatible clinical sign onset or killed at 250 days post inoculation. All mice were tested for presence of abnormal PrP deposition in brain. Incubation period in mice are presented in days (+/−SD). When less than 3 mice were positive, individual incubation period are given. In parallel the same homogenates were tested by PMCA (using tg338 mice brain homogenate as substrate). Each sample was run in 5 replicates for 2 successive rounds and the number of positive reactions is presented.