Ebola is not a good candidate either, it kills too quickly, immobilizing the victim in its wake.
Viruses that kill too quickly evolve to work more slowly in order to spread itself more.
It is not in a germ's best interest to kill its host.
It is also not a particularly good candidate for airborne transmission. It appears the primary disease transmision of Ebola HF is contact with blood or body fluids of an infected people. In the Sudan, where the virus originated, entire families would be wiped out in trying to care for one infected member. Nosocomial transmission (in a hospital) is also a frequent origin for ebola outbreaks. Most of the time, care-givers in African hospitals will not take any self-protective measures (mask, gloves, gowns, etc) to prevent the spread of the disease.