That's obvious, and too late. The USDA quarantines every horse that comes into the country to protect against certain diseases that would destroy that industry. Waiting until symptoms appear is way too late, as by that time the other horses stable together with the first are in trouble.
Dogs, as well as fruit bats, can carry the ebola virus. Heaven help us if some ebola patient falls over in a park and the local feral dogs check it out. Or a friendly dog simply licks the face of somebody sweating from a slight fever.
It's just not as simple as the CDC/NIH keep insisting.
Then governors in the US would than have to quarantine everyone (be they at that point asymptomatic or symptomatic) that came into contact with someone like Hickox or Vinson, even if someone like Hickox or Vinson was asymptomatic, too.