Table 2.
Incubation period of VRQ/VRQ TSE-free recipient sheep transfused with whole blood collected from three VRQ/VRQ sheep and one ARR/ARR sheep, all orally inoculated with PG127 classical scrapie isolatea
| Donors | Incubation period (days) and PrPSc status at dpi: |
|||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 30 |
60 |
90 |
130 |
190 |
||||||
| Incubation (days) | PrPSc status | Incubation (days) | PrPSc status | Incubation (days) | PrPSc status | Incubation (days) | PrPSc status | Incubation (days) | PrPSc status | |
| D4 | >450 | − | >450 | − | >450 | − | 184 | + | 161 | + |
| D5 | >450 | − | >450 | − | 184 | + | 168 | + | 184 | + |
| D6 | >450 | − | >450 | − | 234 | + | 184 | + | 161 | + |
| C1 | >450 | − | >450 | − | >450 | − | >450 | − | >450 | − |
Three susceptible VRQ/VRQ sheep (identified as D4, D5, and D6) and one resistant ARR/ARR sheep (C1) 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 three VRQ/VRQ sheep died 217, 206, and 217 days postinoculation (dpi), whereas the ARR/ARR sheep is still alive (>1,500 days). In VRQ/VRQ donors, the occurrence of scrapie 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. At different time points, whole blood (180 to 200 ml) was collected from each donor and transfused to TSE-free VRQ/VRQ recipients within the 12 h following collection. Recipients were observed until the occurrence of clinical signs. At 450 days after transfusion, recipients that were apparently still healthy were killed. The incubation periods in recipients are presented. All recipients were tested for the presence of abnormal PrP deposition in brain and various lymphoid tissues by immunohistochemistry.