IBD in ball pythons acts far faster than it does in boas. So when a BP gets IBD it tends to die fairly quickly(within a month or two) as opposed to a boa who can carry it for years possibly.

It is also relatively rare in BPs for that reason. It's difficult to spread from BP to BP when there's no contact, and because they tend to die fairly soon after infection, they don't harbor it from hatching until years later.

Added to that, there's no way to rule out IBD without testing the brain, in addition to the liver and blood. So even if you tested blood and it was negative, the vet can't say "Yes, your snake is IBD free". This is the reason why breeders don't go around testing for IBD.

I would be more inclined to think your snake has a respiratory infection.

(all my IBD info is from the UF vet college herp vets, knowledgeable breeders and several online articles/places... but there may be more up-to-date information or recent developments I am not aware of)