Hamster with mites? Or something?

[limabean]

We've had our hamster for just about a year, and he's always been healthy. We feed/water him daily, give him exercise, and clean his cage once a week.

Today we set up a maze for him and were watching him try to find an apple slice, and I noticed a sore on his back. I picked him up to look more closely, and he's missing fur in a long narrow strip across his lower back, and the skin looks inflamed. At first I thought maybe he somehow scraped it on his igloo, or always rested in the same spot with his back pressed up against something (because it's such a defined, long narrow line of fur loss), but then I noticed that he was scratching an awful lot and I started to worry about mites.

I cleaned his cage and everything in it (and didn't see any mites in the cage or on the hamster), replaced the bedding, cleaned the blocks we had used for the maze, and washed everyone's hands really well, but the stuff I'm reading online about hamster mites is freaking me out -- it says to isolate the hamster in its own room to prevent the spread of mites during treatment, but we don't have a spare room. I guess I could move him into the garage? The cage is in my DS's room and it's grossing me out to think of mites or contagious disease in there (and obviously I feel bad for the hamster, who is clearly not happy). What else can I do? Mite spray? I hate to use poison without verifying that there really are mites -- is there a way to tell for sure? 

[JamieCatheryn]

Food Grade Diatomaceous Earth, a white powder of fossilized diatoms, is great for killing all kinds of mite, worms, ants, and roaches, and is pretty much harmless to mammals and birds (a little drying to skin maybe). You can dust animals with it or even mix a little in with their food if there's an internal problem. We use it in our corners throughout the house whenever there's sign of bugs. Farmers use it for livestock a lot.