...I just Googled "hamsters mites" and got a whole page of hits. This is what the first one
http://www.petwebsite.com/mites.htm said:
Mites are usually transferred by contact with other animals or from hay containing mites.
The mites will irritate the hamster's skin and so the may hamster scratch excessively. The skin may also appear sore and there may be some fur loss. On close inspection the mites may be seen as small specks moving through the coat of the hamster. Some mites are more easily seen in the dark under torch light.
Mild cases of mite infestations can be treated with an anti-mite spray designed for caged birds or small animals available from pet shops. The head of the hamster should be shielded to avoid spraying into the eyes and the body sprayed. The cage should be cleaned, sprayed with the anti-mite spray and clean bedding should be provided. This treatment should be repeated as directed on the anti-mite spray.
Hamsters suffering from mites should be isolated from any other hamsters or animals and be placed in a room of their own to avoid spreading mites to other animals.
If mild cases fail to improve within a day or two or in cases of severe mite infestation, or if signs of Mange develop veterinary treatment should be sought. A vet can take a skin scraping to confirm the hamster has mites.