I have this compulsive need to make fiction obey at least some of the laws of reality, and be internally consistant on the ones they break XD It's like some sort of horrible brain-sickness.

And off the top of my head, the symptoms of Geostigma lead me to think Jenova cells tend to reside in connective tissue rather than the bloodstream, which I think would make it's transmissability relatively low.

(SEE?)