There are other viruses that afflict snakes - take Iridoviruses for example. Iridoviruses often present with cutaneous abscesses and - by the very fact that it is a virus - inclusion bodies.
Just so we are clear on this all just about this, inclusion bodies are structures that show up within the cytoplasm or cell nuclei when a virus multiplies. They are not unique to IBD. Just because histology shows inclusion bodies isn't an indicator of IBD. It's an indicator of a multiplying virus. The virus must then be identified. It is imperative that when a potential new virus rears it's head that affected snakes be properly necropsied and that tissue samples are sent to labs that actually research these pathogens. Sending a sample to a diagnostic lab does very little unless that lab is clued into the various researchers identifying these viruses.
As for IBD, it can remain asymptomatic INDEFINATELY.
Not 6 months, not two years, not 5 years.
INDEFINATELY.