Prevention of scrapie transmission in sheep, using embryo transfer

Warren C. Foote From the Animal, Dairy and Veterinary Sciences Department, Utah State University, Logan, UT 84322-4815. (Foote, Maciulis, Call, Evans), the USDA, Animal and Plant Health Inspection Service, Veterinary Services, Scrapie Investigation Center, Mission, TX 78572 (Clark, de Camp), the USDA, Animal and Plant Health Inspection Service, Veterinary Services, Hyattsville, MD 20782 (Hourrigan); and the Utah Department of Agriculture, Salt Lake City, UT 84116 (Marshall).

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Wilber Clark From the Animal, Dairy and Veterinary Sciences Department, Utah State University, Logan, UT 84322-4815. (Foote, Maciulis, Call, Evans), the USDA, Animal and Plant Health Inspection Service, Veterinary Services, Scrapie Investigation Center, Mission, TX 78572 (Clark, de Camp), the USDA, Animal and Plant Health Inspection Service, Veterinary Services, Hyattsville, MD 20782 (Hourrigan); and the Utah Department of Agriculture, Salt Lake City, UT 84116 (Marshall).

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Alma Maciulis From the Animal, Dairy and Veterinary Sciences Department, Utah State University, Logan, UT 84322-4815. (Foote, Maciulis, Call, Evans), the USDA, Animal and Plant Health Inspection Service, Veterinary Services, Scrapie Investigation Center, Mission, TX 78572 (Clark, de Camp), the USDA, Animal and Plant Health Inspection Service, Veterinary Services, Hyattsville, MD 20782 (Hourrigan); and the Utah Department of Agriculture, Salt Lake City, UT 84116 (Marshall).

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Jay W. Call From the Animal, Dairy and Veterinary Sciences Department, Utah State University, Logan, UT 84322-4815. (Foote, Maciulis, Call, Evans), the USDA, Animal and Plant Health Inspection Service, Veterinary Services, Scrapie Investigation Center, Mission, TX 78572 (Clark, de Camp), the USDA, Animal and Plant Health Inspection Service, Veterinary Services, Hyattsville, MD 20782 (Hourrigan); and the Utah Department of Agriculture, Salt Lake City, UT 84116 (Marshall).

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James Hourrigan From the Animal, Dairy and Veterinary Sciences Department, Utah State University, Logan, UT 84322-4815. (Foote, Maciulis, Call, Evans), the USDA, Animal and Plant Health Inspection Service, Veterinary Services, Scrapie Investigation Center, Mission, TX 78572 (Clark, de Camp), the USDA, Animal and Plant Health Inspection Service, Veterinary Services, Hyattsville, MD 20782 (Hourrigan); and the Utah Department of Agriculture, Salt Lake City, UT 84116 (Marshall).

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R. Cole Evans From the Animal, Dairy and Veterinary Sciences Department, Utah State University, Logan, UT 84322-4815. (Foote, Maciulis, Call, Evans), the USDA, Animal and Plant Health Inspection Service, Veterinary Services, Scrapie Investigation Center, Mission, TX 78572 (Clark, de Camp), the USDA, Animal and Plant Health Inspection Service, Veterinary Services, Hyattsville, MD 20782 (Hourrigan); and the Utah Department of Agriculture, Salt Lake City, UT 84116 (Marshall).

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Michael R. Marshall From the Animal, Dairy and Veterinary Sciences Department, Utah State University, Logan, UT 84322-4815. (Foote, Maciulis, Call, Evans), the USDA, Animal and Plant Health Inspection Service, Veterinary Services, Scrapie Investigation Center, Mission, TX 78572 (Clark, de Camp), the USDA, Animal and Plant Health Inspection Service, Veterinary Services, Hyattsville, MD 20782 (Hourrigan); and the Utah Department of Agriculture, Salt Lake City, UT 84116 (Marshall).

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Margarete de Camp From the Animal, Dairy and Veterinary Sciences Department, Utah State University, Logan, UT 84322-4815. (Foote, Maciulis, Call, Evans), the USDA, Animal and Plant Health Inspection Service, Veterinary Services, Scrapie Investigation Center, Mission, TX 78572 (Clark, de Camp), the USDA, Animal and Plant Health Inspection Service, Veterinary Services, Hyattsville, MD 20782 (Hourrigan); and the Utah Department of Agriculture, Salt Lake City, UT 84116 (Marshall).

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Summary

Reciprocal embryo transfers were made between scrapie-inoculated and scrapie-free sheep (Cheviot and Suffolk breeds) to measure scrapie transmission via the embryo (using offspring from embryos of scrapie-inoculated donors and scrapie-free recipients) and via the uterus (using offspring from embryos of scrapie-free donors and scrapie-inoculated recipients taken by cesarean section). Two control groups of offspring, 1 from scrapie-free parents (negative) and 1 from scrapie-inoculated parents (positive), also were included. All sheep were observed for clinical signs of scrapie until death or for a minimum of 60 months. Final diagnosis was made on the basis of histopathologic findings or results 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 embryos from scrapie-inoculated donors, developed scrapie. Also, none of the offspring observed to ≥ 24 months of age from reciprocal cross, via embryo (0/67), or via the uterus (0/25), or from the negative-control group (0/33) developed scrapie. Fifty-six of the offspring via embryo, 19 of these via the uterus, and 31 negative controls survived to ≥ 60 months of age. Of the 21 sheep in the positive-control group, 2 (9.5%) developed scrapie, 1 at 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 to the disease. Results indicate that under the conditions of these experiments, scrapie was not transmitted to the offspring via the embryo or the uterus.

Summary

Reciprocal embryo transfers were made between scrapie-inoculated and scrapie-free sheep (Cheviot and Suffolk breeds) to measure scrapie transmission via the embryo (using offspring from embryos of scrapie-inoculated donors and scrapie-free recipients) and via the uterus (using offspring from embryos of scrapie-free donors and scrapie-inoculated recipients taken by cesarean section). Two control groups of offspring, 1 from scrapie-free parents (negative) and 1 from scrapie-inoculated parents (positive), also were included. All sheep were observed for clinical signs of scrapie until death or for a minimum of 60 months. Final diagnosis was made on the basis of histopathologic findings or results 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 embryos from scrapie-inoculated donors, developed scrapie. Also, none of the offspring observed to ≥ 24 months of age from reciprocal cross, via embryo (0/67), or via the uterus (0/25), or from the negative-control group (0/33) developed scrapie. Fifty-six of the offspring via embryo, 19 of these via the uterus, and 31 negative controls survived to ≥ 60 months of age. Of the 21 sheep in the positive-control group, 2 (9.5%) developed scrapie, 1 at 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 to the disease. Results indicate that under the conditions of these experiments, scrapie was not transmitted to the offspring via the embryo or the uterus.

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