More detail should be included for the petition to be successful.
What about travelers and US citizens from these affected African countries who gain entry into our country via flights from Europe or elsewhere? It is not just the flights, it is the people who are carriers of the virus that we should be addressing.
When is the crisis in Africa considered over? Is that a time stamp declared by WHO or our own CDC?
Also, it should be understood that healthcare workers who choose to enter these countries (experiencing uncontrolled viral spread) do so at their own risk, and will not necessarily be retrieved/flown out.
National quarantine and containment standards need to be set into law to eliminate the risk of an intra-US outbreak, while our government also determines the safest foreign policy regarding the US border containment.

#6: -  

 Excellent questions....these are things that came to my mind as well. How will we track and stop persons from the affected areas from entering the U.S. other than direct flights?