Thanks everyone. I've never dealt with this before, so wasn't sure what it was. I definitely won't ever feed a rat that was out that long ever again. Not worth the risk, even if it wasn't part of the problem. I will keep handling to a minimum, definitely. I refill his water bowl every day, so no change there.

I appreciate all the advice, I will keep this post updated on how he is doing and if I see anything concerning.