Only because of the overwhelming good experiences we had with it back in the Glades days, and the few times I ever had to use it in my breeding colony, and because of the bad experiences I had with No-Pest Strips, I am inclined to blame a bad experience more on something about a particular situation than on the Sevin dust. For example, maybe the snake already had an existing condition, such as a respiratory problem, or maybe the extremely bad shed is complicating matters. Or maybe this snake has absorbed some of the last mite treatment and has not yet excreted it, and the Sevin is compounding it. Or maybe he somehow inhaled a bunch, although I never had one do that. I just don't know what happened, and can only tell of my own experience.
As for Nix, the bad stories I had heard (I never used it myself) were from people who had only used it once. Maybe they used it improperly, or too strong of a solution. Somebody had another thread here about using a diluted treatment of it and having it work well. I can't really comment, good or bad, since I haven't tried it.
I would be curious about the dead snakes from Sevin that somebody (I'm sorry, can't remember names at all) posted they saw at work (at a vet clinic, I guess). I would like to hear more details. I would especially be interested in bad experiences from experienced people who have dealt with the problem several times, rather than strictly new keepers who tried Sevin on their very encounter with mites. I have a feeling that sometimes new keepers might miss some small observation about the condition of their snake, the treatment, the environment, etc. A person who has dealt with it before might be able to provide some really good info as to why they think it worked or didn't. But I would also be interested in hearing about experiences from novices too, so I can pass it on to others as questions get asked.
Unfortunately, we don't have many (any?) objective studies to go by. Just anecdotal evidence. Maybe somebody would like to do a school science project and treat a bunch of snakes with various methods and record the positive and negative results. That would great!
In the meantime, if you have already treated with Sevin and some other chemicals, I would be sure to let the vet know. More chemicals could be a real problem, but hopefully the vet is enough of a chemist to keep it safe.
BTW, a friend of mine recently had mites on her albino Burmese python. She didn't want to use any pesticide, so she went to the local exotic vet. The vet told her to soak it in Betadine and then oil. Didn't tell her how long to soak it, so she soaked it overnight. The snake was dead the next morning. And it was very healthy, except for the mites.
I just don't know of anything really foolproof, but as I said, can only relate the experiences I have had.
Sure hope your pet makes a good recovery.
