Understanding animal movements to inform bovine tuberculosis surveillance: A framework for a targeted approach

Bovine tuberculosis (bTB) is a zoonotic disease that affects domestic and wildlife species. In recent years in the US, a novel scenario for bTB has arisen, characterized by sporadic outbreaks in cattle populations across the country and by spillover of the infection to wildlife. The cattle production system in the US continues to change, with the number of cattle farms declining but the number of cattle per farm increasing. Furthermore, cattle are moved long distances for trade and production purposes. Also the drought has encouraged a large number of cattle to move from severely affected southern states to northern states, such as Minnesota with available feed and water resources. This reality poses a threat to the biosecurity of the Minnesota cattle population and agricultural industry, due to the risk of introduction of bTB from which the state is now free. The objective of the studies presented here was to develop a new framework for bTB surveillance based on risk profiling of herds and regions. The fundamental concept from which the current work originates is that infectious disease transmission is not a random process but is modulated by risk factors that enhance its occurrence. The primarily concern in disease-free areas such as the state of Minnesota should be the identification of those key players, in this case farms and/or regions, that are at higher risk of disease introduction, and secondly to identify those farms and/or regions that would cause greater impact in the cattle population and wildlife populations if infected. The ultimate goal is to develop a targeted approach to bTB surveillance in order to increase system accuracy and cost-effectiveness which, although effective in the past, has failed recently to prevent continuing outbreaks in US cattle and wildlife populations. The combination of the studies presented in this doctoral dissertation provides a systems approach to bTB surveillance, especially at the wildlife and cattle interface. It develops a framework for a targeted surveillance system by developing approaches to identify at risk cattle premises and regions where disease is both more likely to be introduced and spread.