A virus that is not excreted that way, but is present in saliva or blood, as Ebola is supposed to be, may still be transmitted by spitting, coughing, sneezing, vomiting, etc. It's simply not as contagious because the load of infective material is less that way. It's still dangerous, and that route may explain why supposedly protected medical personnel actually aren't.
There is, as well, the possibility that with a mutation the Ebola virus could be excreted through the lung mucosa. It doesn't appear that it has yet but it could. That would be a whole new ballgame.
That's what my highly dated education in the topic tells me. I'll happily be corrected by anyone with better information and training, in fact, I'd appreciate it.