What you are thinking of is IBD, Inclusion Body Disease... you can get more information with google and http://www.anapsid.org/ibd.html

It is a virus, and usually non-fatal to boas who can carry the disease and wipe out entire collections of pythons without the boas displaying any symptoms themselves. The 'cheapest' and most horrific test is to keep a ball python in a mite-infested room with a suspected boa... if it dies in 4 months you have IBD. I'm not sure if there is another publically available test for IBD... though coming from a life sciences background I know you'd need tissue with a high viral load and access to a centrifuge to test for it in the lab.

You might find some 'business' threads where someone bashes big breeders for not putting down research money to develop a real test for IBD... but it would almost be easier to find a cure, and that would take considerable research monies. Best bet now is to house boas and pythons completely separately in your home/facility, handle the pythons first, observe other quarantine measures, buy from reputable dealers, and keep your pythons safe.