Poularde, thank you so much for sharing my yolk of shame. It does lighten the burden when I hear others admit to their own trials and loss. I have managed to save three birds from mites this year and this was my methods (if anyone should be interested)
A bath is nice for quick relief of those biters already on them but only one bath is needed at the outset.
First ivermectin pour on, twice given at about 10 days apart and then a frontline application.
The bird must be sheltered from the hubbub of competition with other birds and from the expenditure of calories by having to fight or run about for food at least at first. And from cold.
Molasses or sugar water- what soda does for us it can do for them-- calories! I even mix in wheat flour sometimes or chicken broth or the gel from chicken soup
Lots and lots of free choice food, esp that which is bad for them as it would be considered bad for us (fatty foods, corn and the like)
With lots and lots of food they do get better, ie build muscle again.
I have not yet seen any more than one recover to a state of breeding, but she is very well and soon to begin laying. It was work but because she is of such a rare breed I feel its worth the work to save her. Its been a few months building her up but she is such a sight to see now and friendly as can be- we call her Fido.
Another note is that if you are looking for mites be sure to look at your males. Three times now its been said that the cockerels are the worst affected. I do not know why this is, but because they are the weaker of the sex as well it is so much easier to lose them to these little biters.
Other people discuss how to treat the coops. I have not done all this as my barn is an old stone one and I can't do much in it. I put down lyme and borax and DE. That's all I can manage. If the mites are starved out then it become maintenance. Treat every bird you get clean or no. You won't see the eggs if there aren't many.