A case-control study on scrapie in Norwegian sheep flocks

Scrapie first was detected in indigenous sheep in Norway in 1981, and from 1995 to 1997 an increase in the number of flocks with scrapie cases was rec orded. These flocks were mainly in one geographical region. A study to iden tify risk factors for scrapie was conducted. The study had three frequency- matched controls selected for every case within the same Veterinary Distric t. A questionnaire was submitted to 176 sheep flocks (42 had been scrapie f locks). The data obtained by the questionnaire were linked to data collecte d from governmental and industry registers. After imputing missing data usi ng single random imputation, the statistical analysis was performed using m ultivariable conditional logistic regression. Purchase of female sheep from scrapie flocks, sharing of rams, or sharing o f pastures between different flocks were the risk factors associated with t he occurrence of scrapie. Of factors potentially sustaining and promoting t he infection in the flock, number of winter-fed sheep, number of buildings for housing sheep, rams and ewes shared room during mating period and incre ase in the flock size were associated with scrapie. We interpret these find ings to show that factors involving transfer of sheep between flocks or dir ect contact between sheep of different flocks are important for the spread of scrapie. Management factors are important for the development of scrapie . However, it was not possible to discriminate between the different manage ment factors in this study at the flock level. Also, factors indicating awa reness and interest of the farmer (as well as willingness to contact a vete rinarian for diseased sheep) were related to the detection of scrapie in th e flock. (C) 2001 Elsevier Science B.V. All rights reserved.