Epidemiology of ovine listeriosis in Great Britain.

A retrospective study of 75 sheep flocks affected with listeriosis during January to June 1982 was made. Seven flocks experienced more than one form of listeriosis. Encephalitis was the commonest form, occurring in 60 flocks, and only lambs were affected in 10 of these flocks. In the remaining 50 flocks only single cases in adults were recorded in eight flocks. The mean attack rate for encephalitis in adults was 2.5 per cent. Listeric abortions occurred in 18 flocks and was the only form of listeriosis in 13 flocks. Silage was fed in 59 of the affected 60 flocks. A significant association between silage feeding and the development of listeric encephalitis was found in these flocks with the estimated relative risk being 3.8. Winter housing was not found to be associated with the development of listeric encephalitis.