I've seen yotes die down to a very small population twice in my life. Both times, it killed the pups in the dens and shortly after they started moving. But I have caught a lot of old coyotes that have the scars from having the mange, and in some cases were in the process of growing their fur back. They are survivers! Now fox.....not so much. Fox get scarcoptic mange, they are DOA.
Now the lice, I have seen yotes clean up from year to year. About four years ago, all I was catching was yotes with lice. I quit on them by thanksgiving, they were so infested. The next year, I didn't catch a single one with lice. Last season, I threw half of the catch away in Ks, and a third in SD. I wish some studys would be done to find out a lot more of how it is propagated, where it comes from in the environment. If you google chewing lice, it just tells what they are but doesn't address they're interaction with canines. It is a wide spread problem that little is actually known about. It has been around for years though, as I saw it back thirty to fourty years ago, but at that time, I thought it was mange that hadn't gotten bad yet! We always called a coyote with a fur problem....mangy!