Hmm ,then I'm afraid we have to differ here, I think they pick up immunity like human babies pick up certain immunities in their mothers milk, obviously baby tortoises have no other way of getting that except from other tortoises .I wonder if The Secret Life of Desert Tortoises would be too slow a process for the likes of Sir David Attenborough,surely they are not as solitary as one is lead to believe. BTW how are you ?