If a single celled virus mutated into something more deadly and resiliant than a strain of it's predecessor, then it would have to reproduce through splitting from the newly designed cell. This would create a new "creature." Is that proof that some god somewhere has made that happen? Of course not. It simply means that the cell naturally needed to evolve and adapt to it's envoronment and did so. Thats just a microcosm of what happens with multi-celled organisms over time. Humans still have appendixes which perform no real function for us today, but they were useful for something at one point in our evolution. Some god isn't just twitching is nose and making things happen. Things happen for scientific reasons.