PREVENTION OF SCRAPIE TRANSMISSION IN SHEEP, USING EMBRYO-TRANSFER

Reciprocal embryo transfers were made between scrapie-inoculated and s crapie-free sheep (Cheviot and Suffolk breeds) to measure scrapie tran smission via the embryo (using offspring from embryos of scrapie-inocu lated donors and scrapie-free recipients) and via the uterus (using of fspring from embryos of scrapie-free donors and scrapie-inoculated rec ipients taken by cesarean section). Two control groups of offspring, 1 from scrapie-free parents (negative) and 1 from scrapie-inoculated pa rents (positive), also were included. All sheep were observed for clin ical signs of scrapie until death or for a minimum of 60 months. Final diagnosis was made on the basis of histopathologic findings or result s of mouse inoculation and/or proteinase-K-resistant protein analysis. Thirty to 61% of the scrapie-inoculated donor/recipient sheep within groups developed scrapie within 8 to 44 months after inoculation. None of the scrapie-free donor/recipients, including those gestating embry os from scrapie-inoculated donors, developed scrapie. Also, none of th e offspring observed to greater than or equal to 24 months of age from reciprocal cross, via embryo (0/67), or via the uterus (0/25), or fro m the negative-control group (0/33) developed scrapie. Fifty-six of th e offspring via embryo, 19 of these via the uterus, and 31 negative co ntrols survived to greater than or equal to 60 months of age. Of the 2 1 sheep in the positive-control group, 2 (9.5%) developed scrapie, 1 a t 31 months of age and 1 at 42 months of age. In the Cheviot offspring , the percentage of sheep carrying the short incubation allele ranged from 24 to 44% and the percentage in the Suffolk offspring ranged from 61 to 83%. These proportions indicate high degree of susceptibility t o the disease. Results indicate that under the conditions of these exp eriments, scrapie was not transmitted to the offspring via the embryo or the uterus.