The influence of selected herd factors and a badger-intervention tuberculosis-control programme on the risk of a herd-level trade restriction to a bovine population in Ireland.

The risk of a trade restriction to cattle herds between 1990-1994, as a result of failing the tuberculin skin test or disclosure of visible lesions in the abattoir, was compared in two areas in East Offaly, Ireland. Cattle herds from the Project area where badgers were systematically removed over a 7-year period (1989-1995) were compared to herds from a Control area where no wildlife-intervention programme had taken place. A Cox proportional hazard model indicated, for example, that the risk of a herd-level trade restriction to herds with 30 animals in the Control area was 1.4 times the risk to similar-sized herds in the Project area. The study provides evidence that a badger-control programme is effective in reducing the risk of a trade restriction to cattle herds as the badger represents an important reservoir of Mycobacterium bovis infection for cattle.

The effect of a badger removal programme on the incidence of tuberculosis in an Irish cattle population.

The risk of a confirmed tuberculous herd restriction was examined using a logistic model for herds involved in the East Offaly Badger Research Project, Ireland, from 1988-1995. Cattle herds present in the badger-removal area had a significantly lower proportion of new confirmed tuberculous herd restrictions compared with cattle from an area where no systematic badger removal was attempted.

The association between the bovine tuberculosis status of herds in the East Offaly Project Area, and the distance to badger setts, 1988-1993.

The proximity of farms to badger setts was compared between farms that had experienced a tuberculosis breakdown and those that had not, over the 6 year period from 1988 to 1993. The data were derived from a badger removal study conducted in East Offaly County in the Republic of Ireland. Badger removal began in 1989 and continued through 1993; by the end of 1990, approximately 80% of all badgers caught in the 6 year period had been removed. All badgers were examined, grossly, for evidence of tuberculosis. Tuberculosis status of the approximately 900 study herds was based on the results of the single intradermal comparative skin test and/or lesions of bovine tuberculosis. All herds were tested at least once annually. The number of herds experiencing bovine tuberculosis declined over the period, particularly in the years 1992 and 1993. The data on farm and badger sett location were stored and analysed, initially, in a geographical information system. Owing to the badger removal programme, the distance between the barn yard of a typical farm and the nearest occupied badger sett increased, by about 300 m year-1, and by about 600 m year-1 to the closest infected sett. In bivariate analyses, in the years 1988 and 1989, the risk of tuberculosis declined with increasing distance to a badger sett containing one or more tuberculous badgers. In multivariable logistic regression analyses, year and the average number of cattle tested per farm per year were controlled. A second identical analysis was conducted to control for the repeated observations on the same herds using generalised estimating equations. In both analyses, the risk of a multiple reactor tuberculosis breakdown decreased for herds at least 1000 m away from an infected badger sett, and increased as the number of infected badgers per infected sett increased. Despite the significantly reduced risk of a breakdown with increasing distance to infected badger setts, the relationship was not strong (sensitivity and specificity of the model in the low 70% range) and explained only 9-19% of tuberculosis breakdowns.