It's not approved in chickens you will be eating the eggs or meat from. But for my sultans I had to use fipronil (active ingredient) dog spot treatment. Knocked the mites out in one dose and I never had to retreat. I was pretty desperate though and had tried 7dust, wood ash, ivermectin and other things. Some of the research I did on it said fertility might suffer but I did not see that problem. I don't eat the eggs or meat since my chickens are ornamental, but it's a spot treatment effective for months I would highly suggest not eating the eggs for that period of time.
Just in case you go this route, I used the treatment for the largest dog I could find. I put 3 drops on my 6lb sultans and 2 drops on d'uccle bantams. I parted the feathers at the upper neck and applied the drops to the skin there. The chickens had no side effects.
