Well, he's wrong. Ask any of the big breeders - NERD, RDR, BHB, the Barkers - all who have worked with hundreds if not thousands of ball pythons - in their experience it is contagious.

Adam has told me that when he breeds, if a male comes down with an RI - the females that he's been with are the most likely to also come down with it.

You can't get more "specialist" than them.