We think it's spread through some sort of telepathic means. At first we were afraid that it was a resurgence of the Pandora virus that had caused us problems a few years back, but the symptoms are very different and after a bit of investigation we concluded that our patient zero must have brought it back from off world. The most notable symptom is irrational violence and an urge to kill. That's part of the reason we put them in stasis; it's safer for everyone that way.