Without outside assistance, none.
In point of fact, an uninfected Congolese villager would be hard put to get to the US without assistance. Congo is landlocked and border control into Uganda and Rwanda would be heightened with Ebola active in Kivu and Ituri provinces. In contrast to the US, other than sneaking in through unguarded regions, border security at normal crossings is strict. Ad hoc roadblocks with spike-laden cement barriers and armed guards is normal. From Kivu/Uturi provinces, travel on lakes might be possible, but where would they go? The Congo River runs into the Atlantic, but from those provinces you would have to travel over half of the river to get there.
IMHO, the main point is that these people are arriving in good shape with clean and relatively unworn clothing. They are being transported all the way by plane or vehicle. They are not walking other than a few miles after the coyotes drop them off. Further, why are people from Central Africa arriving now in the US. This is not normal from what I have read.
The pre-patent period for Ebola is a wide range - from 2-21 days - during this period the patient is non-infectious.
Dylan said it in "Ballad of A Thin Man"
"Because something is happening here
But ya' don't know what it is
Do you, Mister Jones?"
When I was in Kenya, a Danish teenager was evac'ed to Denmark with early symptoms of a hemorrhagic fever - it was Marburg. He was dead in a week. He got it from fresh bat shit hitting his skin in a cave where I had been 3 times.
As a microbiologist, the African hemorrhagic fevers are the most terrifying - Ebola, Marburg, Lassa and others.
My main point in this is that if it gets here, and cases exceed our BSL-IV capacity (20 or less beds nationwide) we are toast. Flu, plague, etc can be treated in normal isolation units, not Ebola or Marburg.
My $0.02 and hardly worth that.
