What is a primary risk factor for the introduction of M. bovis into US cattle herds?

The primary risk factor for the introduction of Mycobacterium bovis (M. bovis) into U.S. cattle herds is the movement of humans and animals from areas where tuberculosis (TB) is prevalent. This highlights the importance of animal and human interactions in the epidemiology of the disease, as pathogens can be transferred through direct contact or indirectly through contaminated environments.

When individuals travel or transport animals from regions with known TB outbreaks, they can inadvertently introduce M. bovis to otherwise healthy herds. The movement of domestic and wild animals, as well as humans who may carry the bacteria on their clothing or equipment, significantly increases the risk of spreading this infectious disease.

While other factors such as the tradition of cattle trading, consumption of unprocessed milk, and wildlife movements do contribute to the overall risk of disease transmission, they are typically secondary to the direct impact of human and animal movement from TB-endemic areas.