A foreign animal disease could potentially enter the U.S. through which of the following?

The transmission of foreign animal diseases can occur through various pathways, and an infected human traveler is one of the potential routes. Humans can act as vectors for certain diseases, transporting pathogens from one area to another on their clothing, belongings, or even through their bodies without necessarily showing symptoms themselves. When travelers come from regions where certain animal diseases are prevalent, they may inadvertently introduce these pathogens to new areas.

In contrast, while unprocessed animal feed can indeed carry pathogens, it is typically less direct in terms of human movement and travel. Domestic pets, while they can carry some diseases, are not the primary concern for foreign animal diseases on a large scale compared to human carriers. Laboratory specimens are tightly regulated and monitored; thus, while they can also introduce diseases, they are less likely to be a source of unintentional introduction compared to infected travelers who may not be subjected to the same level of scrutiny.