In regards to diagnosis:
An interesting note is that, to my knowledge, all information available on IBD is derived from a 5 page essay written by Elliot Jacobson. You'll notice his name repeatedly in the reference list above, and others listed would be basing research on what he has compiled. The fact of the matter is that IBD is not of major importance to those who fund scientific experiments, and little, if any work has been done apart from Elliot's. If you contact him at the University above, he will personally send you a copy of his essay.
What this means is that any vet or breeder that has diagnostic info on IBD are all, literally, reading the same book. Variations in opinions most likely result from reading derivative, and at times misinterpreted, info as can be expected with any generational communication.
Talking to many vets, who in turn have spoken with many other vets and pathologists on both sides of the borders alike, i have been led to believe that the key statement in the quote above is that the absence of inclusion bodies in a biopsy does not determine the absence of IBD. It just means that no inclusion bodies, also called fat, were found in places from which tissue was taken- which is typically the liver, kidney, blood, or the CNS.
To take this back a couple steps, it's interesting to look at the nature of lab testing and virus's themselves.
Lab values, such as an increase in leukocytes, can tell the pathologist that "something" is going on- that the body is mounting a counterattack to either a baceria or virus. Other tests can actually determine which one it is. But virus's, particularly retrovirus's like HIV and IBD, are especially tricky because they actually sit INSIDE of a cell's DNA- cutting and pasting themselves within it, until the host can no longer discern the virus from itself. The body fails to recognize, and therefore respond to, the invading virus. As a result, retrovirus testing is often a search not for the virus itself, but for a syndome, or collection of symptoms that imply a viral infection. In the case of IBD, this syndrome is comprised primarily of inclusion bodies (fat), found in all the wrong places. THIS IS ALL THEY ARE LOOKING FOR. Not the virus, but fat. In fact, an IBD virus has not even been isolated yet, but researchers, based on the bodies physiological responses to some kind of microbial invasion, feel they have every reason to strongly believe in just such a virus. Because other factors could possibly cause abberant fat bodies, there are even some people who do not even share the scientific belief in IBD's existence. That point aside, it is important to understand that an informed vet, who has actually done his research an not just consulted their garden variety Veterinary Manual, is most likely to tell you that IBD cannot be positively confirmed by any means other than a full necropsy.
"There's nothing more freeing than to be confined to live only in what you know is true..." John DeRuiter-