Generally mites only hang out on your snake to feed (and they are nocturnal) - when they are done feeding they drop off and go for a little walk - looking for nice places to lay eggs. They can also travel pretty far so you need to remember that not only do you have to treat your snake and it's cage - but also your racks and/or surrounding area. They lay eggs in your carpet, corners of your walls, furniture everywhere and the eggs can stay dormant for several months. If you've had the snake out or handled it a lot - you could have been tracking the mites all over your house.
After you have cleaned and/or treated everything - its a pretty good idea to keep treating at least the snakes general area for several months - every time you clean a cage treat it with Provent A Mite (PAM) treat the racks as well and keep a mite trap or two near your snake cage. If you were lucky enough to see the mites and cleaned and treated the snake before it entered your home - simply keeping it in a PAM treated cage with a mite trap near by should be enough to insure that anything that escaped the initial treatment gets killed before being able to reproduce.
Good luck!!
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Tosha 
JET Pythons