It depends on many factors of the disease...how contagious, how quickly it shows symptoms, how quickly it kills. If it's quick in all factors, shutting down transportation and letting it ride out is the safest way, but not most humane. If it spreads easily, but doesn't show up for a while, it could go anywhere.
Frank Herbert's "The White Plague" showed one way politically how the world would react...not pretty. Basically a "it's your problem not ours" attitude.