Here's some info I posted on a previous thread:
Testing isn't conclusive. The only way to test for it is by doing a liver biopsy, which is very expensive... and hasn't been proven. It's possible a snake can test positive for inclusion bodies and not actually have IBD.

I like to explain IBD like this: it is the AIDS for snakes, though much faster acting in BPs. It breaks down the immune system so that the snake actually dies from an RI or neurological disorder rather than from IBD. Nasty stuff...

Boas are carriers of the disease. It can take long periods of time for them to begin showing symptoms of it---stargazing, chronic RIs, mouth rot, eventually degrading into neurological problems such as striking at random and being unable to roll over when placed on their backs. BPs, however, will begin showing symptoms almost immediately... there have been cases where someone will bring a boa into their collection and it will show no signs of being sick. Once introduced directly into the collection, however, their other boids start getting sick and dying.

No one's really sure how it's passed. Possibly through the air, but definitely through touching, sharing cages, water bowls, etc.

Fact is, we really don't know that much about it. The only way to get rid of it, once it's in a collection, is to immediately dispose of the infected animals... and personally, I wouldn't ever trust a cage or anything that an infected animal has used. I would get rid of everything like that too.

So that's the break-down. The way it was introduced sounded as if boas were the culprit of the disease, which isn't true. All boids can have and/or spread IBD... it is NOT boa exclusive. They simply catch a lot of flak for being carriers.

It's a pretty rare disease... though I did read a scary article on another forum yesterday---posted by someone that had actually gone through IBD spread himself---stating that more cases of IBD are found during necropsies than are actually shared with the public. People keep it hidden when one of their snake's dies from IBD because they don't want the stigma of the disease to be associated with their business. I can pull up the numbers... it was a scary percentage and made me think.