There are several viruses that are airborne or can be transmitted by mites that can jump host and even use YOU as transportation, now as far as the specific virus known in Boas and for which there is no cure it is IBD which is tricky since Boas can be asymptomatic for years.
You have to know that there is a possibility that your Boa is a carrier but there is a possibility of anything with any species you bring in (such as OPMV that can also ravage a collection) which is why quarantine is ESSENTIAL. Now those two diseases are rare and trust me if a breeder had either in their collection people would know. and I would expect them to do the right thing which is close their collection off.
Now keep in mind that Boas can be asymptomatic for YEARS (which make even 6 months quarantine can prove useless if the animal is a carrier), the good news is that there is a blood test that can give you the peace of mind you need and know that your Boa is healthy and not a carrier.
Personally if I was to buy a Boa I would QT (like I do any snake), and I would get the test done before housing it in the same room than my other animals.
Here is a good read http://ball-pythons.net/forums/showt...f-Up-About-IBD