First off i am not a doctor....so all the info i am supplying is my opinion and knowledge.....
I have never in my time working with animals heard of anyone having seizures related to snakes. It seems odd that he gets them after handling his animals........
If he had salmonella he would have other symptoms....i.e. dehydration/diherrea/vomiting and just a general crappy feeling.........
I would suspect that there is something deeper going on..........has he been checked by neurologists ( im sure he has...but it cant hurt to ask.......) ITs possible that he has something going on with his brain....other than the seizure issue.......(tumor growth??) Has he had any brain injury/trauma in the past that could have affected him now? What else is goin on in his daily routine that could cause it? (drug use? not sure of his age....sorry...)
There is a lot to look at..........but i dont think the snake has much if anything to do with it.........
I have been around them for a long time......especially working in a summer camp & animal theme park with kids who had medical condiotions.........some of which also had seizures......and handling snakes & crocodilians never affected any of them in any way......again.......these were my observations.....
I hope you figure out the problem..........
Send them my best regards.........and tell him to get well soon!
Jared Horenstein
Royal Python Reptiles