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Epidemiologic analysis of reported scrapie in sheep in the United States: 1,117 cases (1947-1992)
N E Wineland1, L A Detwiler, M D Salman
1Center for Animal Health Monitoring, Veterinary Services, USDA-APHIS, Fort Collins, CO 80521, USA.
Objective:
To determine epidemiologic features associated with reported cases of scrapie in sheep in the United States.
Design:
Retrospective study.
Sample Population:
Records for scrapie-positive sheep flocks and sheep with clinical signs consistent with scrapie reported to the USDA from 1947 through 1992.
Procedure:
Records from the USDA's scrapie control and eradication program were abstracted, entered into a computer database, and statistically analyzed.
Results:
1,117 sheep from 657 flocks located in 39 states were scrapie positive during the study period. Seasonal or spatial trends were not evident. Mean yearly proportion of scrapie-positive flocks increased slightly from 1965 through 1992. One hundred sixty-eight rams and 949 ewes were reported to be scrapie positive during the study period, which was slightly more rams than expected if the disease was equally likely to affect rams and ewes. Suffolks (972/1,117; 87%) and Hampshires (68/1,117; 6%) were most commonly affected.
Clinical Implications:
The prevalence of scrapie in sheep in the United States is unknown. Bias in this study may have resulted from inconsistencies in available information, misclassification of sheep with clinically suspicious signs of scrapie, and changes in the national scrapie control and eradication program that likely affected willingness of owners and veterinarians to report potentially infected sheep.