Actually, it has.
Before...1990ish i believe. Outside of Washington DC, in Reston Virginia. Monkeys got it... it didnt kill any humans though. Search for "Ebola reston" for some more info. Also, the book by Richard Preston "The Hot Zone" is all about that one event, and ebola in general... a really great book! Not for the faint hearted though.. made me wash my hands every two minutes when i read it.
PS - Ebola comes originally from Africa, not Africa and Australia. Comes from the Zaire River region..