Inclusion Body Disease (IBD) is like the boogeyman in the closet. It's a disease that is attributed to everything from neurological issues (caused by heat, stress, parasites, etc), to respiratory issues and every other little "off" things snakes do.
If you purchase your animal from a reputable dealer, IBD shouldn't be an issue.
Also, I'd like to add that you should quarantine evey new animal, but this wouldn't help stop IBD. As animals can carry IBD for years without symptoms.
From the sounds of it though, you don't have to worry about IBD spreading through your collection since it is boid specific. Colubrids can not get IBD.
OH wow, I did not know that. Thanks for the helpfull info everyone. I dont plan on having more than one Boa, but you know how that goes..lol thats what i said about the first snake i got.