You can have various biopsies done on a live snake - liver, esophageal tonsils, kidneys, gall bladder, etc.
I've had them done on animals in my collection.
They are not 100% reliable only because the biopsied organ needs to have identifiable inclusion cells in it to make a diagnosis.
Absence of inclusion cells does not necessarily mean the animal is disease free - it just means that the organ biopsied is free of inclusion cells. They are also not cheap.
To say that there are no reliable tests on living animals to screen or check for IBD is blatantly false.
http://www.reptilechannel.com/reptil...y-disease.aspx
http://www.boa-constrictors.com/com/Haltung/IBDEng.htm