Not even theoretically feasible...
No matter how intelligent that ape became, and I mean you could replace it's brain with a computer, it wouldn't be able to speak. One theory as to why human evolved to a more advanced species away from other primates is the development of our larynx. Why do you think that [even exceptionally intelligent] gorillas have to be taught sign language to communicate with humans? Their tongues and larynx's don't work in accordance enough to produce complex sounds, and that's a fact of their anatomy, not intelligence.
Secondly, since the apes and homo sapiens are in the same biological order, how is it that the virus destroys the homo sapiens body (by presumably attacking the nervous or respiratory system), but when the primates inhale it, their brain power is increased?