Thanks all. We've actually been dealing with this for about 8 months. They started showing symptoms about a month after they came to me, so the change in environment or stress of moving could have triggered the inability to fight the infection. They'd get better, then sick, then we'd treat them, then get better, then sick again. It was just a vicious cycle they couldn't beat.

The previous owner and I communicate back and forth frequently, so he knows all about what happened. All the other snakes I've gotten from him (except for the lesser) never had any signs of any illness and are growing and eating and thriving.

I really think it's just one of those freak things, but I know I won't mess around with RI's in the future (not that we did this time).