This paper presents the results of the first formal epidemiological study in Northern Ireland of risk factors for bovine tuberculosis (TB) associated with farm boundaries, neighbours and wildlife. The study was designed as a case-control study and 427 dairy herds were investigated between December 1993 and January 1995. The case herds had more than 30 cattle, and herds in which the source of infection had been ascribed to purchased cattle were avoided. Data on the Department of Agriculture Animal Health Computer were used in conjunction with data collected through a questionnaire to examine a range of possible risk factors, including the number and nature of the farm boundaries, the number of neighbours and their TB history, the number of hedgerows, the presence of badger setts, whether badger carcases had been found on the land, and the possible presence of deer. A follow-up telephone survey was conducted to minimise bias. The results highlighted two main associations with TB breakdowns, the presence of badgers, and contiguous neighbours who had had confirmed TB breakdowns. The estimated aetiological fraction for both associations was approximately 40 per cent, suggesting that although infected cattle may have a significant role in the transmission of TB their importance relative to the badger may have been over-estimated in the Northern Ireland TB scheme. The contribution of the badger is possibly one of several main reasons for the lack of significant progress in TB eradication despite strenuous efforts associated with all aspects of the scheme.

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The epidemiology of bovine spongiform encephalopathy (BSE) in Northern Ireland from 1988, when it was first confirmed, to the end of 1995 is described. All cases of BSE were subjected to a detailed epidemiological investigation, complemented by data from the national animal health records on every bovine animal. Data are presented on 1680 cases. Many of the epidemiological features of the disease were similar to those reported in Great Britain, but the incidence in Northern Ireland was approximately one-tenth that in Great Britain. The epidemic increased to a peak of 56 cases per month in January 1994, and decreased to nine cases in December 1995. Statutory intervention banning the use of meat and bone meal in ruminant feed in January 1989 has produced a marked and continuing reduction in the incidence. The majority of the cases were in Northern Ireland cattle, but 83 cases were imported from Great Britain and five from the Republic of Ireland. Many of the key epidemiological features have remained constant throughout the epidemic: the greater incidence of BSE in dairy herds than in beef suckler herds, the low within-herd incidence, the variation in incidence with herd size, the breed distribution, the distribution of the reported clinical signs and the proportion of purchased cases. Although the source of the BSE epidemic in Northern Ireland has not been established conclusively, the evidence suggests that the importation of meat and bone meal and protein concentrates from Great Britain may have been responsible.

patterns in the NI epidemic reveals signi¢cant clustering of cases in herds and counties. The observed clustering of cases within herds results in lower per capita incidence of BSE in previously una¡ected herds, providing support for the introduction of a certi¢ed herd scheme in NI. By ¢tting a backcalculation model to the case data, we can estimate the number of animals infected with the aetiological agent of BSE and project the number of future cases. We predict that the epidemic will decline rapidly, with approximately 99 cases (95% con¢dence interval: 30, 504) occurring in the ¢ve year period 1997^2001.