[Hekomi]

My guess is mites too. I don't know how things differ geographically but my go to is revolution (selamectin). It's very very safe. You can get it from your vet and hamsters require just one drop on the back of the neck. We use this on any new hamsters and any hamsters leaving our house.

You'll need to either toss, bake or freeze all the wood toys. When we had a hamster bring mites into our house, we dosed all our hamsters with revolution, put them on paper towel bedding, just a hut, wheel, food dish and bottle. We cleaned them out weekly and minimized contact. We gave everyone two doses of revolution (three weeks apart) to ensure we caught the lifecycle.

It sounds like they also may exist environmentally. Do you have a cat? If not, I would suggest purchasing permethrin spray which will kill any mites and bugs on carpet, furniture and human bedding. I wouldn't recommend using this in the cage.