Reducing the Public Health Impact of Bovine Tuberculosis by Controlling Disease Transmission Between Cattle and White-Tailed Deer in Northwestern Minnesota

Bovine tuberculosis, caused by infection with Mycobacterium bovis, is a re-emerging zoonotic disease. It has staged a comeback by establishing infections in wildlife and cattle, creating the potential for human disease in locations where it was thought to be under control. In northwestern Minnesota, infected cattle and white-tailed deer were first discovered in 2005. A major bovine tuberculosis eradication campaign is underway in the state, with multiple efforts employed to control M. bovis infection in both cattle and deer populations. In order to effectively eradicate bovine tuberculosis in Minnesota, there is a need for better understanding of the factors that increase the risk of deer and cattle interacting in a way that facilitates tuberculosis transmission. By reducing the risk of disease transmission within the animal populations, we will also reduce the risk that bovine tuberculosis will again become a common disease in human populations. The purpose of this study is to characterize the risk of interactions between cattle and white-tailed deer in northern Minnesota in order to prevent M. bovis transmission. A survey originally developed to assess deer-cattle interactions in Michigan was modified for use in Minnesota, introducing a scoring method to evaluate the areas of highest priority at risk of potential deer-cattle interaction. The resulting semi-quantitative deer-cattle interaction risk assessment was used at 53 cattle herds located in the region adjacent to the bovine tuberculosis " Core Area ". Two evaluators each scored the farm separately, and then created a management plan for the farm that prioritized the areas of greatest risk for deer-cattle interactions. Herds located within the " Management Zone " were evaluated by Minnesota Board of Animal Health staff, and results from these surveys were used as a point of comparison. Half the herds visited by the University of Minnesota group had experienced deer damage to stored feeds within the past year. Only 11% of herds reported that deer were most frequently seen in the winter, while spring, summer, or fall were more common times for 50% of the herds. A strong association was found between increasing percentage of land that would serve as deer cover and the presence of deer damage to stored feeds on the farm. Farms most often had deer damage to stored hay, although the feed with highest proportion of damage by deer was silage. Cattle feeding practices were also found to have increased risk for deer-cattle interactions, with average scores for …