Which of the following is a risk factor for the introduction of M. bovis into cattle herds in the US?

The introduction of Mycobacterium bovis, the bacterium that causes bovine tuberculosis (bTB), into cattle herds in the U.S. is significantly influenced by the movement of humans and animals from areas where the disease is prevalent. B. bovis is transmissible between animals and can also be spread through contaminated environments. When individuals or livestock travel from regions with existing bTB cases, they can inadvertently bring the pathogen with them, increasing the risk of spreading the disease to previously uninfected herds.

The other options, while relevant to broader discussions about livestock health and disease management, do not specifically address the direct mechanisms by which M. bovis is typically introduced into U.S. cattle herds. For example, while the export of livestock is a consideration, it generally involves regulated processes that include health checks, which may reduce the risk. High dairy product consumption is linked to demand rather than the spread of the disease, and natural habitat loss is more associated with ecological changes that can influence wildlife diseases rather than directly introducing bTB into cattle.