In any case, the most I got out of understanding what origin its from is that there were rumors it was genetically engineered, and that the U.S. was later blamed for it. But from what I gather, they blamed the U.S. because of the FEV info leaked-which, according to the wiki, was in part and/or originally (or at least supposedly, in part/originally) made to destroy the New Plague. It wasn't the origin-again, unless I'm stupidly missing something I should have caught on to.
Is it simply unknown? Because suddenly the question of the source of it's creation is beginning to nag me.