If there are lots of "biological surprises" waiting for us outside our borders, then Americans and legal travelers of all kinds are already bringing them to us -- that's the way our global economy works. And the real scare, of course, is what will happen as the changing climate broadens the ranges of things like West Nile Virus and Dengue, that we have not had much experience with . . . but I digress.
As long as you call these people who are migrating across our border (yes! against the law: it's not legal, or safe) "illegals", it gives you permission to see them as objects and disease vectors, and so to perpetuate this conservative illogic. Now, in an Einsteinian thought experiment, imagine we have tremendously stout borders, and all the "huddled masses yearning to breathe free" who have migrated from our southern borders are in some sort of holding camps in Mexico (how inhumane -- but I digress . . . .) If their hypothetical diseases are also animal-borne, then we'll have them; if exclusively human-borne, business and tourist travelers will bring them to us. . . . But perhaps instead we should imagine that what you want is no more tourism, no more business travel (I guess we could sacrifice our standard of living to please you?). Even so, diseases of various kinds are still here in the US, and the only way to stamp them out comprehensively, even with all our borders closed, is comprehensive vaccination, which appears to scare you as much as immigration does.
