Don't use Diatamaceous Earth!!! That stuff is friggin messy as all getup. You'll have dust everywhere in no time, and it doesn't work. It does work on indivudual louse, but the amount you have to use, and dusting the cages, you'll hate the stuff... Not to mention, while it is safe for consumption, breathing it in can be hazardous. It works like little knives, rough microscopic edges, that break the louse's exoskeleton, causing it to dehydrate to death. But, enough of it breathed in, can cause irritation to your lungs.... Trust me, I've been down that road...

As for Provent a Mite, yes the stuff works wonders, but it's too expensive to use in each cage, even though it lasts an entire month. PAM is made with permitherin. That is the mite/louse killing agent in it. Go down to Home Depot/ACE/Lowes, get a gallon of Bed Bug and Flea spray, made by Hot Shot, uses permitherin, a slighly lower percentage, .2% to PAM's .5%.
Spray the cage, not the animals. I spray around the edge of each tub every single week when I clean. While it won't kill the mites on the rats themselves, they won't have anywhere to go, and will die shortly. You will thank me later, trust me on this... I've been using it for a long long time. When I buy it, I always get funny looks, because I usually buy the store out!
I use it on my entire buildings, inside and out about once a month. It works! Don't try all the hocus pocus mumbo gumbo, they don't work, or barely work, I've tried them all.

As for infestation, rat lice are species specific, so they won't infest other animals, not even mice. Mice get mites too, but a different species. They will however, try them out! We used to get a flare up every once and a while before I found the permitherin. They will bite humans as well, but they don't feed on us, but it's annoying as all.

When we moved into our new buildings a couple of years ago, we got absolutely infested. I brought in two seperate pest companies, one wouldn't even touch us for fear of killing animals, the other tried, but failed miserably. Once I started using Hot Shot, they started dying off, and within a weeks period, were off the animals, looking for new places to go, because I couldn't spray inside my store(fish,birds,reptiles, etc) it took another week to 10 days before they died off completely.
I use it religiously now, and the absolute only time I ever see, feel a mite, is when I bring in animals from another source, and they don't last long.