foxfly
If your theory about cabin air were correct, the crew that work on the aircraft semi-permanently might logically be expected to be in a continual state of sickness, as would their families and friends at home. This is not the case.
In fact, aircraft use
HEPA filters that restrict the presence of pathogens in recirculated air.
HEPA filters
won't protect you from the person sitting next to you, or, for example, those that touch the toilet door knob without washing their hands. This kind of transmission is almost certainly what has affected you in the past. I would suggest sani-wipes might be a help?
The way to combat some diseases (I can't speak for ebola) might be at airports on arrival à la SARS - temperature scanners and so forth.