After some time, I'd place some money on that cultist head priest. She seems to have a cunning smile.
She might not be the one to infect/poison Kugel, but as the highest ranked human around, maybe striker transfered control to her when Kugel died.
That would be a more down to Earth idea.

As for the way Kugel died, either killed or not, the only result is that it served her purpose of getting her hand on Striker and reinforce the cult's tyranny (and her position)