Jemma | Kitty
My initial analysis based off the description of a mist and seeing what Hydra was trying to do was that it was a virus, meant to cause world wide extinction, as well as the fact that one person died in the temple, one person was drastically changed and killed people and then another I thought had somehow managed to escape it but it turns out she hadn't. The DNA change from before and after was vast.
The fact that it seems that there has been DNA modifications means that theory is wrong, and that it's biology.