Just delt with this myself and spent a week researching it, so heres what you do.
Basicly they are mange mites, nasty little buggers but theres hope. Now there are a few diffrent ways you can fight this. One of them involes going to the feed store and doseing your rats with a product called ivomec. Its a paste used for worming horses. You give your rats a rice grain size dose on days 1,7 and 15. It fights the mites from the inside out. There are however a few drawbacks to this method #1 is ivermectin, the active ingedient in ivomec, stays in your rats for 30 days after the last dose so they are no good for feeders until then. #2 is ivermectin has been shown to be passed from mother to offspring in milk and it kills your pinks. So there no good for breeders either. #3 is it is very easy to overdose your rats with ivomec.
Ivomec is better but harder to get right and your production shuts down.
Fortunately there is an easier way.
Go to any of the big box stores or your pet store and pick up a flea and tick spray for use on Cats and Kittens what your looking for as the ingredient is Permethrin between.05 and .06 % as long as its good for cats you are good to go. Dog flea and tick spray will kill them. Mange mites have a 21 day life cycle so you need to treat for 3 weeks. Spray down rat and bedding on day 1,7, and 15. Just be sure to rinse any rat that has been sprayed or been kept on sprayed bedding before you use it as a feeder. Using this method feeding and feeder production can go on as usual without having to call a lhalt to the whole thing.
Now then all that being said. I am on week two of trying the spray method I have used sprayed and rinsed rats as feeders with no ill effects. I got the method from a local person who breeds rodents for feeders on a large scale. The ivomec method I got of various places on the internet, mostly from pet rat sites who use it because they dont have the issue of having to feed off a medicated rat.