This reminds me of another keeper, she had no new snakes introduced (I think), but let someone handle her snakes, who had recently lost her own snake to a mysterious disease, and unfortunetly she did lose her whole collection.

[edit]
Is the Boa in the same room?

I'm not one to blame IBD, but it does rattle you a bit when a snake gets sick for no reason. Hopefully it is treatable and will have little to no side effects.