US Customs and Public Health Officials Attempt to Stop Infected

U.S. Customs and public health officials attempt to stop infected travelers, but why is this not always so easy?

A) Travelers often claim a "right to travel" and ignore them.
B) Some diseases attack the brain, telling them that they're fine.
C) Infected individuals may not be visibly ill when they cross a U.S. Border.
D) Traveler's often opt for the treatment option, even when it doesn't always work, just so they can get where they want to go.